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Home</a> | </li> <li><a href="index.html">Documentation</a>»</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="body" role="main"> <div class="section" id="commandline-2-0-library-manual"> <h1>CommandLine 2.0 Library Manual<a class="headerlink" href="#commandline-2-0-library-manual" title="Permalink to this headline">¶</a></h1> <div class="contents local topic" id="contents"> <ul class="simple"> <li><a class="reference internal" href="#introduction" id="id8">Introduction</a></li> <li><a class="reference internal" href="#quick-start-guide" id="id9">Quick Start Guide</a><ul> <li><a class="reference internal" href="#boolean-arguments" id="id10">Boolean Arguments</a></li> <li><a class="reference internal" href="#argument-aliases" id="id11">Argument Aliases</a></li> <li><a class="reference internal" href="#selecting-an-alternative-from-a-set-of-possibilities" id="id12">Selecting an alternative from a set of possibilities</a></li> <li><a class="reference internal" href="#named-alternatives" id="id13">Named Alternatives</a></li> <li><a class="reference internal" href="#parsing-a-list-of-options" id="id14">Parsing a list of options</a></li> <li><a class="reference internal" href="#collecting-options-as-a-set-of-flags" id="id15">Collecting options as a set of flags</a></li> <li><a class="reference internal" href="#adding-freeform-text-to-help-output" id="id16">Adding freeform text to help output</a></li> <li><a class="reference internal" href="#grouping-options-into-categories" id="id17">Grouping options into categories</a></li> </ul> </li> <li><a class="reference internal" href="#reference-guide" id="id18">Reference Guide</a><ul> <li><a class="reference internal" href="#positional-options" id="id19">Positional Arguments</a><ul> <li><a class="reference internal" href="#specifying-positional-options-with-hyphens" id="id20">Specifying positional options with hyphens</a></li> <li><a class="reference internal" href="#determining-absolute-position-with-getposition" id="id21">Determining absolute position with getPosition()</a></li> <li><a class="reference internal" href="#the-cl-consumeafter-modifier" id="id22">The <code class="docutils literal notranslate"><span class="pre">cl::ConsumeAfter</span></code> modifier</a></li> </ul> </li> <li><a class="reference internal" href="#internal-vs-external-storage" id="id23">Internal vs External Storage</a></li> <li><a class="reference internal" href="#option-attributes" id="id24">Option Attributes</a></li> <li><a class="reference internal" href="#option-modifiers" id="id25">Option Modifiers</a><ul> <li><a class="reference internal" href="#hiding-an-option-from-help-output" id="id26">Hiding an option from <code class="docutils literal notranslate"><span class="pre">-help</span></code> output</a></li> <li><a class="reference internal" href="#controlling-the-number-of-occurrences-required-and-allowed" id="id27">Controlling the number of occurrences required and allowed</a></li> <li><a class="reference internal" href="#controlling-whether-or-not-a-value-must-be-specified" id="id28">Controlling whether or not a value must be specified</a></li> <li><a class="reference internal" href="#controlling-other-formatting-options" id="id29">Controlling other formatting options</a></li> <li><a class="reference internal" href="#miscellaneous-option-modifiers" id="id30">Miscellaneous option modifiers</a></li> <li><a class="reference internal" href="#response-files" id="id31">Response files</a></li> </ul> </li> <li><a class="reference internal" href="#top-level-classes-and-functions" id="id32">Top-Level Classes and Functions</a><ul> <li><a class="reference internal" href="#the-cl-getregisteredoptions-function" id="id33">The <code class="docutils literal notranslate"><span class="pre">cl::getRegisteredOptions</span></code> function</a></li> <li><a class="reference internal" href="#the-cl-parsecommandlineoptions-function" id="id34">The <code class="docutils literal notranslate"><span class="pre">cl::ParseCommandLineOptions</span></code> function</a></li> <li><a class="reference internal" href="#the-cl-parseenvironmentoptions-function" id="id35">The <code class="docutils literal notranslate"><span class="pre">cl::ParseEnvironmentOptions</span></code> function</a></li> <li><a class="reference internal" href="#the-cl-setversionprinter-function" id="id36">The <code class="docutils literal notranslate"><span class="pre">cl::SetVersionPrinter</span></code> function</a></li> <li><a class="reference internal" href="#the-cl-opt-class" id="id37">The <code class="docutils literal notranslate"><span class="pre">cl::opt</span></code> class</a></li> <li><a class="reference internal" href="#the-cl-list-class" id="id38">The <code class="docutils literal notranslate"><span class="pre">cl::list</span></code> class</a></li> <li><a class="reference internal" href="#the-cl-bits-class" id="id39">The <code class="docutils literal notranslate"><span class="pre">cl::bits</span></code> class</a></li> <li><a class="reference internal" href="#the-cl-alias-class" id="id40">The <code class="docutils literal notranslate"><span class="pre">cl::alias</span></code> class</a></li> <li><a class="reference internal" href="#the-cl-extrahelp-class" id="id41">The <code class="docutils literal notranslate"><span class="pre">cl::extrahelp</span></code> class</a></li> <li><a class="reference internal" href="#the-cl-optioncategory-class" id="id42">The <code class="docutils literal notranslate"><span class="pre">cl::OptionCategory</span></code> class</a></li> </ul> </li> <li><a class="reference internal" href="#builtin-parsers" id="id43">Builtin parsers</a></li> </ul> </li> <li><a class="reference internal" href="#extending-the-library" id="id44">Extension Guide</a><ul> <li><a class="reference internal" href="#writing-a-custom-parser" id="id45">Writing a custom parser</a></li> <li><a class="reference internal" href="#exploiting-external-storage" id="id46">Exploiting external storage</a></li> <li><a class="reference internal" href="#dynamically-adding-command-line-options" id="id47">Dynamically adding command line options</a></li> </ul> </li> </ul> </div> <div class="section" id="introduction"> <h2><a class="toc-backref" href="#id8">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2> <p>This document describes the CommandLine argument processing library. It will show you how to use it, and what it can do. The CommandLine library uses a declarative approach to specifying the command line options that your program takes. By default, these options declarations implicitly hold the value parsed for the option declared (of course this <a class="reference internal" href="#can-be-changed">can be changed</a>).</p> <p>Although there are a <strong>lot</strong> of command line argument parsing libraries out there in many different languages, none of them fit well with what I needed. By looking at the features and problems of other libraries, I designed the CommandLine library to have the following features:</p> <ol class="arabic simple"> <li>Speed: The CommandLine library is very quick and uses little resources. The parsing time of the library is directly proportional to the number of arguments parsed, not the number of options recognized. Additionally, command line argument values are captured transparently into user defined global variables, which can be accessed like any other variable (and with the same performance).</li> <li>Type Safe: As a user of CommandLine, you don’t have to worry about remembering the type of arguments that you want (is it an int? a string? a bool? an enum?) and keep casting it around. Not only does this help prevent error prone constructs, it also leads to dramatically cleaner source code.</li> <li>No subclasses required: To use CommandLine, you instantiate variables that correspond to the arguments that you would like to capture, you don’t subclass a parser. This means that you don’t have to write <strong>any</strong> boilerplate code.</li> <li>Globally accessible: Libraries can specify command line arguments that are automatically enabled in any tool that links to the library. This is possible because the application doesn’t have to keep a list of arguments to pass to the parser. This also makes supporting <a class="reference internal" href="#dynamically-loaded-options">dynamically loaded options</a> trivial.</li> <li>Cleaner: CommandLine supports enum and other types directly, meaning that there is less error and more security built into the library. You don’t have to worry about whether your integral command line argument accidentally got assigned a value that is not valid for your enum type.</li> <li>Powerful: The CommandLine library supports many different types of arguments, from simple <a class="reference internal" href="#boolean-flags">boolean flags</a> to <a class="reference internal" href="#scalars-arguments">scalars arguments</a> (<a class="reference internal" href="#strings">strings</a>, <a class="reference internal" href="#integers">integers</a>, <a class="reference internal" href="#enums">enums</a>, <a class="reference internal" href="#doubles">doubles</a>), to <a class="reference internal" href="#lists-of-arguments">lists of arguments</a>. This is possible because CommandLine is…</li> <li>Extensible: It is very simple to add a new argument type to CommandLine. Simply specify the parser that you want to use with the command line option when you declare it. <a class="reference internal" href="#custom-parsers">Custom parsers</a> are no problem.</li> <li>Labor Saving: The CommandLine library cuts down on the amount of grunt work that you, the user, have to do. For example, it automatically provides a <code class="docutils literal notranslate"><span class="pre">-help</span></code> option that shows the available command line options for your tool. Additionally, it does most of the basic correctness checking for you.</li> <li>Capable: The CommandLine library can handle lots of different forms of options often found in real programs. For example, <a class="reference internal" href="#positional">positional</a> arguments, <code class="docutils literal notranslate"><span class="pre">ls</span></code> style <a class="reference internal" href="#grouping">grouping</a> options (to allow processing ‘<code class="docutils literal notranslate"><span class="pre">ls</span> <span class="pre">-lad</span></code>’ naturally), <code class="docutils literal notranslate"><span class="pre">ld</span></code> style <a class="reference internal" href="#prefix">prefix</a> options (to parse ‘<code class="docutils literal notranslate"><span class="pre">-lmalloc</span> <span class="pre">-L/usr/lib</span></code>’), and interpreter style options.</li> </ol> <p>This document will hopefully let you jump in and start using CommandLine in your utility quickly and painlessly. Additionally it should be a simple reference manual to figure out how stuff works.</p> </div> <div class="section" id="quick-start-guide"> <h2><a class="toc-backref" href="#id9">Quick Start Guide</a><a class="headerlink" href="#quick-start-guide" title="Permalink to this headline">¶</a></h2> <p>This section of the manual runs through a simple CommandLine’ification of a basic compiler tool. This is intended to show you how to jump into using the CommandLine library in your own program, and show you some of the cool things it can do.</p> <p>To start out, you need to include the CommandLine header file into your program:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span> <span class="cpf">"llvm/Support/CommandLine.h"</span><span class="cp"></span> </pre></div> </div> <p>Additionally, you need to add this as the first line of your main program:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">argv</span><span class="p">)</span> <span class="p">{</span> <span class="n">cl</span><span class="o">::</span><span class="n">ParseCommandLineOptions</span><span class="p">(</span><span class="n">argc</span><span class="p">,</span> <span class="n">argv</span><span class="p">);</span> <span class="p">...</span> <span class="p">}</span> </pre></div> </div> <p>… which actually parses the arguments and fills in the variable declarations.</p> <p>Now that you are ready to support command line arguments, we need to tell the system which ones we want, and what type of arguments they are. The CommandLine library uses a declarative syntax to model command line arguments with the global variable declarations that capture the parsed values. This means that for every command line option that you would like to support, there should be a global variable declaration to capture the result. For example, in a compiler, we would like to support the Unix-standard ‘<code class="docutils literal notranslate"><span class="pre">-o</span> <span class="pre"><filename></span></code>’ option to specify where to put the output. With the CommandLine library, this is represented like this:</p> <div class="highlight-c++ notranslate" id="here"><span id="scalars-arguments"></span><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">OutputFilename</span><span class="p">(</span><span class="s">"o"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Specify output filename"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">value_desc</span><span class="p">(</span><span class="s">"filename"</span><span class="p">));</span> </pre></div> </div> <p>This declares a global variable “<code class="docutils literal notranslate"><span class="pre">OutputFilename</span></code>” that is used to capture the result of the “<code class="docutils literal notranslate"><span class="pre">o</span></code>” argument (first parameter). We specify that this is a simple scalar option by using the “<code class="docutils literal notranslate"><span class="pre">cl::opt</span></code>” template (as opposed to the “<code class="docutils literal notranslate"><span class="pre">cl::list</span></code>” template), and tell the CommandLine library that the data type that we are parsing is a string.</p> <p>The second and third parameters (which are optional) are used to specify what to output for the “<code class="docutils literal notranslate"><span class="pre">-help</span></code>” option. In this case, we get a line that looks like this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">o</span> <span class="o"><</span><span class="n">filename</span><span class="o">></span> <span class="o">-</span> <span class="n">Specify</span> <span class="n">output</span> <span class="n">filename</span> </pre></div> </div> <p>Because we specified that the command line option should parse using the <code class="docutils literal notranslate"><span class="pre">string</span></code> data type, the variable declared is automatically usable as a real string in all contexts that a normal C++ string object may be used. For example:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="p">...</span> <span class="n">std</span><span class="o">::</span><span class="n">ofstream</span> <span class="n">Output</span><span class="p">(</span><span class="n">OutputFilename</span><span class="p">.</span><span class="n">c_str</span><span class="p">());</span> <span class="k">if</span> <span class="p">(</span><span class="n">Output</span><span class="p">.</span><span class="n">good</span><span class="p">())</span> <span class="p">...</span> <span class="p">...</span> </pre></div> </div> <p>There are many different options that you can use to customize the command line option handling library, but the above example shows the general interface to these options. The options can be specified in any order, and are specified with helper functions like <a class="reference internal" href="#cl-desc">cl::desc(…)</a>, so there are no positional dependencies to remember. The available options are discussed in detail in the <a class="reference internal" href="#reference-guide">Reference Guide</a>.</p> <p>Continuing the example, we would like to have our compiler take an input filename as well as an output filename, but we do not want the input filename to be specified with a hyphen (ie, not <code class="docutils literal notranslate"><span class="pre">-filename.c</span></code>). To support this style of argument, the CommandLine library allows for <a class="reference internal" href="#positional">positional</a> arguments to be specified for the program. These positional arguments are filled with command line parameters that are not in option form. We use this feature like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">InputFilename</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<input file>"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">init</span><span class="p">(</span><span class="s">"-"</span><span class="p">));</span> </pre></div> </div> <p>This declaration indicates that the first positional argument should be treated as the input filename. Here we use the <a class="reference internal" href="#cl-init">cl::init</a> option to specify an initial value for the command line option, which is used if the option is not specified (if you do not specify a <a class="reference internal" href="#cl-init">cl::init</a> modifier for an option, then the default constructor for the data type is used to initialize the value). Command line options default to being optional, so if we would like to require that the user always specify an input filename, we would add the <a class="reference internal" href="#cl-required">cl::Required</a> flag, and we could eliminate the <a class="reference internal" href="#cl-init">cl::init</a> modifier, like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">InputFilename</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<input file>"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">Required</span><span class="p">);</span> </pre></div> </div> <p>Again, the CommandLine library does not require the options to be specified in any particular order, so the above declaration is equivalent to:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">InputFilename</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">Required</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<input file>"</span><span class="p">));</span> </pre></div> </div> <p>By simply adding the <a class="reference internal" href="#cl-required">cl::Required</a> flag, the CommandLine library will automatically issue an error if the argument is not specified, which shifts all of the command line option verification code out of your application into the library. This is just one example of how using flags can alter the default behaviour of the library, on a per-option basis. By adding one of the declarations above, the <code class="docutils literal notranslate"><span class="pre">-help</span></code> option synopsis is now extended to:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">o</span> <span class="o"><</span><span class="n">filename</span><span class="o">></span> <span class="o">-</span> <span class="n">Specify</span> <span class="n">output</span> <span class="n">filename</span> </pre></div> </div> <p>… indicating that an input filename is expected.</p> <div class="section" id="boolean-arguments"> <h3><a class="toc-backref" href="#id10">Boolean Arguments</a><a class="headerlink" href="#boolean-arguments" title="Permalink to this headline">¶</a></h3> <p>In addition to input and output filenames, we would like the compiler example to support three boolean flags: “<code class="docutils literal notranslate"><span class="pre">-f</span></code>” to force writing binary output to a terminal, “<code class="docutils literal notranslate"><span class="pre">--quiet</span></code>” to enable quiet mode, and “<code class="docutils literal notranslate"><span class="pre">-q</span></code>” for backwards compatibility with some of our users. We can support these by declaring options of boolean type like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Force</span> <span class="p">(</span><span class="s">"f"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Enable binary output on terminals"</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Quiet</span> <span class="p">(</span><span class="s">"quiet"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Don't print informational messages"</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Quiet2</span><span class="p">(</span><span class="s">"q"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Don't print informational messages"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">Hidden</span><span class="p">);</span> </pre></div> </div> <p>This does what you would expect: it declares three boolean variables (“<code class="docutils literal notranslate"><span class="pre">Force</span></code>”, “<code class="docutils literal notranslate"><span class="pre">Quiet</span></code>”, and “<code class="docutils literal notranslate"><span class="pre">Quiet2</span></code>”) to recognize these options. Note that the “<code class="docutils literal notranslate"><span class="pre">-q</span></code>” option is specified with the “<a class="reference internal" href="#cl-hidden">cl::Hidden</a>” flag. This modifier prevents it from being shown by the standard “<code class="docutils literal notranslate"><span class="pre">-help</span></code>” output (note that it is still shown in the “<code class="docutils literal notranslate"><span class="pre">-help-hidden</span></code>” output).</p> <p>The CommandLine library uses a <a class="reference internal" href="#different-parser">different parser</a> for different data types. For example, in the string case, the argument passed to the option is copied literally into the content of the string variable… we obviously cannot do that in the boolean case, however, so we must use a smarter parser. In the case of the boolean parser, it allows no options (in which case it assigns the value of true to the variable), or it allows the values “<code class="docutils literal notranslate"><span class="pre">true</span></code>” or “<code class="docutils literal notranslate"><span class="pre">false</span></code>” to be specified, allowing any of the following inputs:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">compiler</span> <span class="o">-</span><span class="n">f</span> <span class="c1"># No value, 'Force' == true</span> <span class="n">compiler</span> <span class="o">-</span><span class="n">f</span><span class="o">=</span><span class="n">true</span> <span class="c1"># Value specified, 'Force' == true</span> <span class="n">compiler</span> <span class="o">-</span><span class="n">f</span><span class="o">=</span><span class="n">TRUE</span> <span class="c1"># Value specified, 'Force' == true</span> <span class="n">compiler</span> <span class="o">-</span><span class="n">f</span><span class="o">=</span><span class="n">FALSE</span> <span class="c1"># Value specified, 'Force' == false</span> </pre></div> </div> <p>… you get the idea. The <a class="reference internal" href="#bool-parser">bool parser</a> just turns the string values into boolean values, and rejects things like ‘<code class="docutils literal notranslate"><span class="pre">compiler</span> <span class="pre">-f=foo</span></code>’. Similarly, the <a class="reference internal" href="#float">float</a>, <a class="reference internal" href="#double">double</a>, and <a class="reference internal" href="#int">int</a> parsers work like you would expect, using the ‘<code class="docutils literal notranslate"><span class="pre">strtol</span></code>’ and ‘<code class="docutils literal notranslate"><span class="pre">strtod</span></code>’ C library calls to parse the string value into the specified data type.</p> <p>With the declarations above, “<code class="docutils literal notranslate"><span class="pre">compiler</span> <span class="pre">-help</span></code>” emits this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">f</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">binary</span> <span class="n">output</span> <span class="n">on</span> <span class="n">terminals</span> <span class="o">-</span><span class="n">o</span> <span class="o">-</span> <span class="n">Override</span> <span class="n">output</span> <span class="n">filename</span> <span class="o">-</span><span class="n">quiet</span> <span class="o">-</span> <span class="n">Don</span><span class="s1">'t print informational messages</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> </pre></div> </div> <p>and “<code class="docutils literal notranslate"><span class="pre">compiler</span> <span class="pre">-help-hidden</span></code>” prints this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">f</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">binary</span> <span class="n">output</span> <span class="n">on</span> <span class="n">terminals</span> <span class="o">-</span><span class="n">o</span> <span class="o">-</span> <span class="n">Override</span> <span class="n">output</span> <span class="n">filename</span> <span class="o">-</span><span class="n">q</span> <span class="o">-</span> <span class="n">Don</span><span class="s1">'t print informational messages</span> <span class="o">-</span><span class="n">quiet</span> <span class="o">-</span> <span class="n">Don</span><span class="s1">'t print informational messages</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> </pre></div> </div> <p>This brief example has shown you how to use the ‘<a class="reference internal" href="#cl-opt">cl::opt</a>’ class to parse simple scalar command line arguments. In addition to simple scalar arguments, the CommandLine library also provides primitives to support CommandLine option <a class="reference internal" href="#aliases">aliases</a>, and <a class="reference internal" href="#lists">lists</a> of options.</p> </div> <div class="section" id="argument-aliases"> <span id="aliases"></span><h3><a class="toc-backref" href="#id11">Argument Aliases</a><a class="headerlink" href="#argument-aliases" title="Permalink to this headline">¶</a></h3> <p>So far, the example works well, except for the fact that we need to check the quiet condition like this now:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="p">...</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Quiet</span> <span class="o">&&</span> <span class="o">!</span><span class="n">Quiet2</span><span class="p">)</span> <span class="n">printInformationalMessage</span><span class="p">(...);</span> <span class="p">...</span> </pre></div> </div> <p>… which is a real pain! Instead of defining two values for the same condition, we can use the “<a class="reference internal" href="#cl-alias">cl::alias</a>” class to make the “<code class="docutils literal notranslate"><span class="pre">-q</span></code>” option an <strong>alias</strong> for the “<code class="docutils literal notranslate"><span class="pre">-quiet</span></code>” option, instead of providing a value itself:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Force</span> <span class="p">(</span><span class="s">"f"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Overwrite output files"</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Quiet</span> <span class="p">(</span><span class="s">"quiet"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Don't print informational messages"</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">alias</span> <span class="n">QuietA</span><span class="p">(</span><span class="s">"q"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Alias for -quiet"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">aliasopt</span><span class="p">(</span><span class="n">Quiet</span><span class="p">));</span> </pre></div> </div> <p>The third line (which is the only one we modified from above) defines a “<code class="docutils literal notranslate"><span class="pre">-q</span></code>” alias that updates the “<code class="docutils literal notranslate"><span class="pre">Quiet</span></code>” variable (as specified by the <a class="reference internal" href="#cl-aliasopt">cl::aliasopt</a> modifier) whenever it is specified. Because aliases do not hold state, the only thing the program has to query is the <code class="docutils literal notranslate"><span class="pre">Quiet</span></code> variable now. Another nice feature of aliases is that they automatically hide themselves from the <code class="docutils literal notranslate"><span class="pre">-help</span></code> output (although, again, they are still visible in the <code class="docutils literal notranslate"><span class="pre">-help-hidden</span> <span class="pre">output</span></code>).</p> <p>Now the application code can simply use:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="p">...</span> <span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">Quiet</span><span class="p">)</span> <span class="n">printInformationalMessage</span><span class="p">(...);</span> <span class="p">...</span> </pre></div> </div> <p>… which is much nicer! The “<a class="reference internal" href="#cl-alias">cl::alias</a>” can be used to specify an alternative name for any variable type, and has many uses.</p> </div> <div class="section" id="selecting-an-alternative-from-a-set-of-possibilities"> <span id="unnamed-alternatives-using-the-generic-parser"></span><h3><a class="toc-backref" href="#id12">Selecting an alternative from a set of possibilities</a><a class="headerlink" href="#selecting-an-alternative-from-a-set-of-possibilities" title="Permalink to this headline">¶</a></h3> <p>So far we have seen how the CommandLine library handles builtin types like <code class="docutils literal notranslate"><span class="pre">std::string</span></code>, <code class="docutils literal notranslate"><span class="pre">bool</span></code> and <code class="docutils literal notranslate"><span class="pre">int</span></code>, but how does it handle things it doesn’t know about, like enums or ‘<code class="docutils literal notranslate"><span class="pre">int*</span></code>’s?</p> <p>The answer is that it uses a table-driven generic parser (unless you specify your own parser, as described in the <a class="reference internal" href="#extension-guide">Extension Guide</a>). This parser maps literal strings to whatever type is required, and requires you to tell it what this mapping should be.</p> <p>Let’s say that we would like to add four optimization levels to our optimizer, using the standard flags “<code class="docutils literal notranslate"><span class="pre">-g</span></code>”, “<code class="docutils literal notranslate"><span class="pre">-O0</span></code>”, “<code class="docutils literal notranslate"><span class="pre">-O1</span></code>”, and “<code class="docutils literal notranslate"><span class="pre">-O2</span></code>”. We could easily implement this with boolean options like above, but there are several problems with this strategy:</p> <ol class="arabic simple"> <li>A user could specify more than one of the options at a time, for example, “<code class="docutils literal notranslate"><span class="pre">compiler</span> <span class="pre">-O3</span> <span class="pre">-O2</span></code>”. The CommandLine library would not be able to catch this erroneous input for us.</li> <li>We would have to test 4 different variables to see which ones are set.</li> <li>This doesn’t map to the numeric levels that we want… so we cannot easily see if some level >= “<code class="docutils literal notranslate"><span class="pre">-O1</span></code>” is enabled.</li> </ol> <p>To cope with these problems, we can use an enum value, and have the CommandLine library fill it in with the appropriate level directly, which is used like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">enum</span> <span class="n">OptLevel</span> <span class="p">{</span> <span class="n">g</span><span class="p">,</span> <span class="n">O1</span><span class="p">,</span> <span class="n">O2</span><span class="p">,</span> <span class="n">O3</span> <span class="p">};</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">OptLevel</span><span class="o">></span> <span class="n">OptimizationLevel</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Choose optimization level:"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">values</span><span class="p">(</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">g</span> <span class="p">,</span> <span class="s">"No optimizations, enable debugging"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">O1</span><span class="p">,</span> <span class="s">"Enable trivial optimizations"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">O2</span><span class="p">,</span> <span class="s">"Enable default optimizations"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">O3</span><span class="p">,</span> <span class="s">"Enable expensive optimizations"</span><span class="p">)));</span> <span class="p">...</span> <span class="k">if</span> <span class="p">(</span><span class="n">OptimizationLevel</span> <span class="o">>=</span> <span class="n">O2</span><span class="p">)</span> <span class="n">doPartialRedundancyElimination</span><span class="p">(...);</span> <span class="p">...</span> </pre></div> </div> <p>This declaration defines a variable “<code class="docutils literal notranslate"><span class="pre">OptimizationLevel</span></code>” of the “<code class="docutils literal notranslate"><span class="pre">OptLevel</span></code>” enum type. This variable can be assigned any of the values that are listed in the declaration. The CommandLine library enforces that the user can only specify one of the options, and it ensure that only valid enum values can be specified. The “<code class="docutils literal notranslate"><span class="pre">clEnumVal</span></code>” macros ensure that the command line arguments matched the enum values. With this option added, our help output now is:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="n">Choose</span> <span class="n">optimization</span> <span class="n">level</span><span class="p">:</span> <span class="o">-</span><span class="n">g</span> <span class="o">-</span> <span class="n">No</span> <span class="n">optimizations</span><span class="p">,</span> <span class="n">enable</span> <span class="n">debugging</span> <span class="o">-</span><span class="n">O1</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">trivial</span> <span class="n">optimizations</span> <span class="o">-</span><span class="n">O2</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">default</span> <span class="n">optimizations</span> <span class="o">-</span><span class="n">O3</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">expensive</span> <span class="n">optimizations</span> <span class="o">-</span><span class="n">f</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">binary</span> <span class="n">output</span> <span class="n">on</span> <span class="n">terminals</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">o</span> <span class="o"><</span><span class="n">filename</span><span class="o">></span> <span class="o">-</span> <span class="n">Specify</span> <span class="n">output</span> <span class="n">filename</span> <span class="o">-</span><span class="n">quiet</span> <span class="o">-</span> <span class="n">Don</span><span class="s1">'t print informational messages</span> </pre></div> </div> <p>In this case, it is sort of awkward that flag names correspond directly to enum names, because we probably don’t want a enum definition named “<code class="docutils literal notranslate"><span class="pre">g</span></code>” in our program. Because of this, we can alternatively write this example like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">enum</span> <span class="n">OptLevel</span> <span class="p">{</span> <span class="n">Debug</span><span class="p">,</span> <span class="n">O1</span><span class="p">,</span> <span class="n">O2</span><span class="p">,</span> <span class="n">O3</span> <span class="p">};</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">OptLevel</span><span class="o">></span> <span class="n">OptimizationLevel</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Choose optimization level:"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">values</span><span class="p">(</span> <span class="n">clEnumValN</span><span class="p">(</span><span class="n">Debug</span><span class="p">,</span> <span class="s">"g"</span><span class="p">,</span> <span class="s">"No optimizations, enable debugging"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">O1</span> <span class="p">,</span> <span class="s">"Enable trivial optimizations"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">O2</span> <span class="p">,</span> <span class="s">"Enable default optimizations"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">O3</span> <span class="p">,</span> <span class="s">"Enable expensive optimizations"</span><span class="p">)));</span> <span class="p">...</span> <span class="k">if</span> <span class="p">(</span><span class="n">OptimizationLevel</span> <span class="o">==</span> <span class="n">Debug</span><span class="p">)</span> <span class="n">outputDebugInfo</span><span class="p">(...);</span> <span class="p">...</span> </pre></div> </div> <p>By using the “<code class="docutils literal notranslate"><span class="pre">clEnumValN</span></code>” macro instead of “<code class="docutils literal notranslate"><span class="pre">clEnumVal</span></code>”, we can directly specify the name that the flag should get. In general a direct mapping is nice, but sometimes you can’t or don’t want to preserve the mapping, which is when you would use it.</p> </div> <div class="section" id="named-alternatives"> <h3><a class="toc-backref" href="#id13">Named Alternatives</a><a class="headerlink" href="#named-alternatives" title="Permalink to this headline">¶</a></h3> <p>Another useful argument form is a named alternative style. We shall use this style in our compiler to specify different debug levels that can be used. Instead of each debug level being its own switch, we want to support the following options, of which only one can be specified at a time: “<code class="docutils literal notranslate"><span class="pre">--debug-level=none</span></code>”, “<code class="docutils literal notranslate"><span class="pre">--debug-level=quick</span></code>”, “<code class="docutils literal notranslate"><span class="pre">--debug-level=detailed</span></code>”. To do this, we use the exact same format as our optimization level flags, but we also specify an option name. For this case, the code looks like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">enum</span> <span class="n">DebugLev</span> <span class="p">{</span> <span class="n">nodebuginfo</span><span class="p">,</span> <span class="n">quick</span><span class="p">,</span> <span class="n">detailed</span> <span class="p">};</span> <span class="c1">// Enable Debug Options to be specified on the command line</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">DebugLev</span><span class="o">></span> <span class="n">DebugLevel</span><span class="p">(</span><span class="s">"debug_level"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Set the debugging level:"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">values</span><span class="p">(</span> <span class="n">clEnumValN</span><span class="p">(</span><span class="n">nodebuginfo</span><span class="p">,</span> <span class="s">"none"</span><span class="p">,</span> <span class="s">"disable debug information"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">quick</span><span class="p">,</span> <span class="s">"enable quick debug information"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">detailed</span><span class="p">,</span> <span class="s">"enable detailed debug information"</span><span class="p">)));</span> </pre></div> </div> <p>This definition defines an enumerated command line variable of type “<code class="docutils literal notranslate"><span class="pre">enum</span> <span class="pre">DebugLev</span></code>”, which works exactly the same way as before. The difference here is just the interface exposed to the user of your program and the help output by the “<code class="docutils literal notranslate"><span class="pre">-help</span></code>” option:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="n">Choose</span> <span class="n">optimization</span> <span class="n">level</span><span class="p">:</span> <span class="o">-</span><span class="n">g</span> <span class="o">-</span> <span class="n">No</span> <span class="n">optimizations</span><span class="p">,</span> <span class="n">enable</span> <span class="n">debugging</span> <span class="o">-</span><span class="n">O1</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">trivial</span> <span class="n">optimizations</span> <span class="o">-</span><span class="n">O2</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">default</span> <span class="n">optimizations</span> <span class="o">-</span><span class="n">O3</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">expensive</span> <span class="n">optimizations</span> <span class="o">-</span><span class="n">debug_level</span> <span class="o">-</span> <span class="n">Set</span> <span class="n">the</span> <span class="n">debugging</span> <span class="n">level</span><span class="p">:</span> <span class="o">=</span><span class="n">none</span> <span class="o">-</span> <span class="n">disable</span> <span class="n">debug</span> <span class="n">information</span> <span class="o">=</span><span class="n">quick</span> <span class="o">-</span> <span class="n">enable</span> <span class="n">quick</span> <span class="n">debug</span> <span class="n">information</span> <span class="o">=</span><span class="n">detailed</span> <span class="o">-</span> <span class="n">enable</span> <span class="n">detailed</span> <span class="n">debug</span> <span class="n">information</span> <span class="o">-</span><span class="n">f</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">binary</span> <span class="n">output</span> <span class="n">on</span> <span class="n">terminals</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">o</span> <span class="o"><</span><span class="n">filename</span><span class="o">></span> <span class="o">-</span> <span class="n">Specify</span> <span class="n">output</span> <span class="n">filename</span> <span class="o">-</span><span class="n">quiet</span> <span class="o">-</span> <span class="n">Don</span><span class="s1">'t print informational messages</span> </pre></div> </div> <p>Again, the only structural difference between the debug level declaration and the optimization level declaration is that the debug level declaration includes an option name (<code class="docutils literal notranslate"><span class="pre">"debug_level"</span></code>), which automatically changes how the library processes the argument. The CommandLine library supports both forms so that you can choose the form most appropriate for your application.</p> </div> <div class="section" id="parsing-a-list-of-options"> <span id="lists"></span><h3><a class="toc-backref" href="#id14">Parsing a list of options</a><a class="headerlink" href="#parsing-a-list-of-options" title="Permalink to this headline">¶</a></h3> <p>Now that we have the standard run-of-the-mill argument types out of the way, lets get a little wild and crazy. Lets say that we want our optimizer to accept a <strong>list</strong> of optimizations to perform, allowing duplicates. For example, we might want to run: “<code class="docutils literal notranslate"><span class="pre">compiler</span> <span class="pre">-dce</span> <span class="pre">-constprop</span> <span class="pre">-inline</span> <span class="pre">-dce</span> <span class="pre">-strip</span></code>”. In this case, the order of the arguments and the number of appearances is very important. This is what the “<code class="docutils literal notranslate"><span class="pre">cl::list</span></code>” template is for. First, start by defining an enum of the optimizations that you would like to perform:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">enum</span> <span class="n">Opts</span> <span class="p">{</span> <span class="c1">// 'inline' is a C++ keyword, so name it 'inlining'</span> <span class="n">dce</span><span class="p">,</span> <span class="n">constprop</span><span class="p">,</span> <span class="n">inlining</span><span class="p">,</span> <span class="n">strip</span> <span class="p">};</span> </pre></div> </div> <p>Then define your “<code class="docutils literal notranslate"><span class="pre">cl::list</span></code>” variable:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">list</span><span class="o"><</span><span class="n">Opts</span><span class="o">></span> <span class="n">OptimizationList</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Available Optimizations:"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">values</span><span class="p">(</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">dce</span> <span class="p">,</span> <span class="s">"Dead Code Elimination"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">constprop</span> <span class="p">,</span> <span class="s">"Constant Propagation"</span><span class="p">),</span> <span class="n">clEnumValN</span><span class="p">(</span><span class="n">inlining</span><span class="p">,</span> <span class="s">"inline"</span><span class="p">,</span> <span class="s">"Procedure Integration"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">strip</span> <span class="p">,</span> <span class="s">"Strip Symbols"</span><span class="p">)));</span> </pre></div> </div> <p>This defines a variable that is conceptually of the type “<code class="docutils literal notranslate"><span class="pre">std::vector<enum</span> <span class="pre">Opts></span></code>”. Thus, you can access it with standard vector methods:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="p">(</span><span class="kt">unsigned</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="n">i</span> <span class="o">!=</span> <span class="n">OptimizationList</span><span class="p">.</span><span class="n">size</span><span class="p">();</span> <span class="o">++</span><span class="n">i</span><span class="p">)</span> <span class="k">switch</span> <span class="p">(</span><span class="n">OptimizationList</span><span class="p">[</span><span class="n">i</span><span class="p">])</span> <span class="p">...</span> </pre></div> </div> <p>… to iterate through the list of options specified.</p> <p>Note that the “<code class="docutils literal notranslate"><span class="pre">cl::list</span></code>” template is completely general and may be used with any data types or other arguments that you can use with the “<code class="docutils literal notranslate"><span class="pre">cl::opt</span></code>” template. One especially useful way to use a list is to capture all of the positional arguments together if there may be more than one specified. In the case of a linker, for example, the linker takes several ‘<code class="docutils literal notranslate"><span class="pre">.o</span></code>’ files, and needs to capture them into a list. This is naturally specified as:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="p">...</span> <span class="n">cl</span><span class="o">::</span><span class="n">list</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">InputFilenames</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<Input files>"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">OneOrMore</span><span class="p">);</span> <span class="p">...</span> </pre></div> </div> <p>This variable works just like a “<code class="docutils literal notranslate"><span class="pre">vector<string></span></code>” object. As such, accessing the list is simple, just like above. In this example, we used the <a class="reference internal" href="#cl-oneormore">cl::OneOrMore</a> modifier to inform the CommandLine library that it is an error if the user does not specify any <code class="docutils literal notranslate"><span class="pre">.o</span></code> files on our command line. Again, this just reduces the amount of checking we have to do.</p> </div> <div class="section" id="collecting-options-as-a-set-of-flags"> <h3><a class="toc-backref" href="#id15">Collecting options as a set of flags</a><a class="headerlink" href="#collecting-options-as-a-set-of-flags" title="Permalink to this headline">¶</a></h3> <p>Instead of collecting sets of options in a list, it is also possible to gather information for enum values in a <strong>bit vector</strong>. The representation used by the <a class="reference internal" href="#cl-bits">cl::bits</a> class is an <code class="docutils literal notranslate"><span class="pre">unsigned</span></code> integer. An enum value is represented by a 0/1 in the enum’s ordinal value bit position. 1 indicating that the enum was specified, 0 otherwise. As each specified value is parsed, the resulting enum’s bit is set in the option’s bit vector:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">bits</span> <span class="o">|=</span> <span class="mi">1</span> <span class="o"><<</span> <span class="p">(</span><span class="kt">unsigned</span><span class="p">)</span><span class="k">enum</span><span class="p">;</span> </pre></div> </div> <p>Options that are specified multiple times are redundant. Any instances after the first are discarded.</p> <p>Reworking the above list example, we could replace <a class="reference internal" href="#cl-list">cl::list</a> with <a class="reference internal" href="#cl-bits">cl::bits</a>:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">bits</span><span class="o"><</span><span class="n">Opts</span><span class="o">></span> <span class="n">OptimizationBits</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Available Optimizations:"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">values</span><span class="p">(</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">dce</span> <span class="p">,</span> <span class="s">"Dead Code Elimination"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">constprop</span> <span class="p">,</span> <span class="s">"Constant Propagation"</span><span class="p">),</span> <span class="n">clEnumValN</span><span class="p">(</span><span class="n">inlining</span><span class="p">,</span> <span class="s">"inline"</span><span class="p">,</span> <span class="s">"Procedure Integration"</span><span class="p">),</span> <span class="n">clEnumVal</span><span class="p">(</span><span class="n">strip</span> <span class="p">,</span> <span class="s">"Strip Symbols"</span><span class="p">)));</span> </pre></div> </div> <p>To test to see if <code class="docutils literal notranslate"><span class="pre">constprop</span></code> was specified, we can use the <code class="docutils literal notranslate"><span class="pre">cl:bits::isSet</span></code> function:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">(</span><span class="n">OptimizationBits</span><span class="p">.</span><span class="n">isSet</span><span class="p">(</span><span class="n">constprop</span><span class="p">))</span> <span class="p">{</span> <span class="p">...</span> <span class="p">}</span> </pre></div> </div> <p>It’s also possible to get the raw bit vector using the <code class="docutils literal notranslate"><span class="pre">cl::bits::getBits</span></code> function:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">unsigned</span> <span class="n">bits</span> <span class="o">=</span> <span class="n">OptimizationBits</span><span class="p">.</span><span class="n">getBits</span><span class="p">();</span> </pre></div> </div> <p>Finally, if external storage is used, then the location specified must be of <strong>type</strong> <code class="docutils literal notranslate"><span class="pre">unsigned</span></code>. In all other ways a <a class="reference internal" href="#cl-bits">cl::bits</a> option is equivalent to a <a class="reference internal" href="#cl-list">cl::list</a> option.</p> </div> <div class="section" id="adding-freeform-text-to-help-output"> <span id="additional-extra-text"></span><h3><a class="toc-backref" href="#id16">Adding freeform text to help output</a><a class="headerlink" href="#adding-freeform-text-to-help-output" title="Permalink to this headline">¶</a></h3> <p>As our program grows and becomes more mature, we may decide to put summary information about what it does into the help output. The help output is styled to look similar to a Unix <code class="docutils literal notranslate"><span class="pre">man</span></code> page, providing concise information about a program. Unix <code class="docutils literal notranslate"><span class="pre">man</span></code> pages, however often have a description about what the program does. To add this to your CommandLine program, simply pass a third argument to the <a class="reference internal" href="#cl-parsecommandlineoptions">cl::ParseCommandLineOptions</a> call in main. This additional argument is then printed as the overview information for your program, allowing you to include any additional information that you want. For example:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">argv</span><span class="p">)</span> <span class="p">{</span> <span class="n">cl</span><span class="o">::</span><span class="n">ParseCommandLineOptions</span><span class="p">(</span><span class="n">argc</span><span class="p">,</span> <span class="n">argv</span><span class="p">,</span> <span class="s">" CommandLine compiler example</span><span class="se">\n\n</span><span class="s">"</span> <span class="s">" This program blah blah blah...</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> <span class="p">...</span> <span class="p">}</span> </pre></div> </div> <p>would yield the help output:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">**</span><span class="n">OVERVIEW</span><span class="p">:</span> <span class="n">CommandLine</span> <span class="n">compiler</span> <span class="n">example</span> <span class="n">This</span> <span class="n">program</span> <span class="n">blah</span> <span class="n">blah</span> <span class="n">blah</span><span class="o">...**</span> <span class="n">USAGE</span><span class="p">:</span> <span class="n">compiler</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">...</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">o</span> <span class="o"><</span><span class="n">filename</span><span class="o">></span> <span class="o">-</span> <span class="n">Specify</span> <span class="n">output</span> <span class="n">filename</span> </pre></div> </div> </div> <div class="section" id="grouping-options-into-categories"> <span id="id1"></span><h3><a class="toc-backref" href="#id17">Grouping options into categories</a><a class="headerlink" href="#grouping-options-into-categories" title="Permalink to this headline">¶</a></h3> <p>If our program has a large number of options it may become difficult for users of our tool to navigate the output of <code class="docutils literal notranslate"><span class="pre">-help</span></code>. To alleviate this problem we can put our options into categories. This can be done by declaring option categories (<a class="reference internal" href="#cl-optioncategory">cl::OptionCategory</a> objects) and then placing our options into these categories using the <a class="reference internal" href="#cl-cat">cl::cat</a> option attribute. For example:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">OptionCategory</span> <span class="n">StageSelectionCat</span><span class="p">(</span><span class="s">"Stage Selection Options"</span><span class="p">,</span> <span class="s">"These control which stages are run."</span><span class="p">);</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Preprocessor</span><span class="p">(</span><span class="s">"E"</span><span class="p">,</span><span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Run preprocessor stage."</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">cat</span><span class="p">(</span><span class="n">StageSelectionCat</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">NoLink</span><span class="p">(</span><span class="s">"c"</span><span class="p">,</span><span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Run all stages except linking."</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">cat</span><span class="p">(</span><span class="n">StageSelectionCat</span><span class="p">));</span> </pre></div> </div> <p>The output of <code class="docutils literal notranslate"><span class="pre">-help</span></code> will become categorized if an option category is declared. The output looks something like</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">OVERVIEW</span><span class="p">:</span> <span class="n">This</span> <span class="ow">is</span> <span class="n">a</span> <span class="n">small</span> <span class="n">program</span> <span class="n">to</span> <span class="n">demo</span> <span class="n">the</span> <span class="n">LLVM</span> <span class="n">CommandLine</span> <span class="n">API</span> <span class="n">USAGE</span><span class="p">:</span> <span class="n">Sample</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="n">General</span> <span class="n">options</span><span class="p">:</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">Display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="nb">list</span> <span class="o">-</span> <span class="n">Display</span> <span class="nb">list</span> <span class="n">of</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="nb">list</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="n">Stage</span> <span class="n">Selection</span> <span class="n">Options</span><span class="p">:</span> <span class="n">These</span> <span class="n">control</span> <span class="n">which</span> <span class="n">stages</span> <span class="n">are</span> <span class="n">run</span><span class="o">.</span> <span class="o">-</span><span class="n">E</span> <span class="o">-</span> <span class="n">Run</span> <span class="n">preprocessor</span> <span class="n">stage</span><span class="o">.</span> <span class="o">-</span><span class="n">c</span> <span class="o">-</span> <span class="n">Run</span> <span class="nb">all</span> <span class="n">stages</span> <span class="k">except</span> <span class="n">linking</span><span class="o">.</span> </pre></div> </div> <p>In addition to the behaviour of <code class="docutils literal notranslate"><span class="pre">-help</span></code> changing when an option category is declared, the command line option <code class="docutils literal notranslate"><span class="pre">-help-list</span></code> becomes visible which will print the command line options as uncategorized list.</p> <p>Note that Options that are not explicitly categorized will be placed in the <code class="docutils literal notranslate"><span class="pre">cl::GeneralCategory</span></code> category.</p> </div> </div> <div class="section" id="reference-guide"> <span id="id2"></span><h2><a class="toc-backref" href="#id18">Reference Guide</a><a class="headerlink" href="#reference-guide" title="Permalink to this headline">¶</a></h2> <p>Now that you know the basics of how to use the CommandLine library, this section will give you the detailed information you need to tune how command line options work, as well as information on more “advanced” command line option processing capabilities.</p> <div class="section" id="positional-options"> <span id="positional-arguments-section"></span><span id="positional-arguments"></span><span id="positional-argument"></span><span id="positional"></span><span id="id3"></span><h3><a class="toc-backref" href="#id19">Positional Arguments</a><a class="headerlink" href="#positional-options" title="Permalink to this headline">¶</a></h3> <p>Positional arguments are those arguments that are not named, and are not specified with a hyphen. Positional arguments should be used when an option is specified by its position alone. For example, the standard Unix <code class="docutils literal notranslate"><span class="pre">grep</span></code> tool takes a regular expression argument, and an optional filename to search through (which defaults to standard input if a filename is not specified). Using the CommandLine library, this would be specified as:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">Regex</span> <span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<regular expression>"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">Required</span><span class="p">);</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">Filename</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<input file>"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">init</span><span class="p">(</span><span class="s">"-"</span><span class="p">));</span> </pre></div> </div> <p>Given these two option declarations, the <code class="docutils literal notranslate"><span class="pre">-help</span></code> output for our grep replacement would look like this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">spiffygrep</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="n">regular</span> <span class="n">expression</span><span class="o">></span> <span class="o"><</span><span class="nb">input</span> <span class="n">file</span><span class="o">></span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> </pre></div> </div> <p>… and the resultant program could be used just like the standard <code class="docutils literal notranslate"><span class="pre">grep</span></code> tool.</p> <p>Positional arguments are sorted by their order of construction. This means that command line options will be ordered according to how they are listed in a .cpp file, but will not have an ordering defined if the positional arguments are defined in multiple .cpp files. The fix for this problem is simply to define all of your positional arguments in one .cpp file.</p> <div class="section" id="specifying-positional-options-with-hyphens"> <h4><a class="toc-backref" href="#id20">Specifying positional options with hyphens</a><a class="headerlink" href="#specifying-positional-options-with-hyphens" title="Permalink to this headline">¶</a></h4> <p>Sometimes you may want to specify a value to your positional argument that starts with a hyphen (for example, searching for ‘<code class="docutils literal notranslate"><span class="pre">-foo</span></code>’ in a file). At first, you will have trouble doing this, because it will try to find an argument named ‘<code class="docutils literal notranslate"><span class="pre">-foo</span></code>’, and will fail (and single quotes will not save you). Note that the system <code class="docutils literal notranslate"><span class="pre">grep</span></code> has the same problem:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ spiffygrep '-foo' test.txt Unknown command line argument '-foo'. Try: spiffygrep -help' $ grep '-foo' test.txt grep: illegal option -- f grep: illegal option -- o grep: illegal option -- o Usage: grep -hblcnsviw pattern file . . . </pre></div> </div> <p>The solution for this problem is the same for both your tool and the system version: use the ‘<code class="docutils literal notranslate"><span class="pre">--</span></code>‘ marker. When the user specifies ‘<code class="docutils literal notranslate"><span class="pre">--</span></code>‘ on the command line, it is telling the program that all options after the ‘<code class="docutils literal notranslate"><span class="pre">--</span></code>‘ should be treated as positional arguments, not options. Thus, we can use it like this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ spiffygrep -- -foo test.txt ...output... </pre></div> </div> </div> <div class="section" id="determining-absolute-position-with-getposition"> <h4><a class="toc-backref" href="#id21">Determining absolute position with getPosition()</a><a class="headerlink" href="#determining-absolute-position-with-getposition" title="Permalink to this headline">¶</a></h4> <p>Sometimes an option can affect or modify the meaning of another option. For example, consider <code class="docutils literal notranslate"><span class="pre">gcc</span></code>’s <code class="docutils literal notranslate"><span class="pre">-x</span> <span class="pre">LANG</span></code> option. This tells <code class="docutils literal notranslate"><span class="pre">gcc</span></code> to ignore the suffix of subsequent positional arguments and force the file to be interpreted as if it contained source code in language <code class="docutils literal notranslate"><span class="pre">LANG</span></code>. In order to handle this properly, you need to know the absolute position of each argument, especially those in lists, so their interaction(s) can be applied correctly. This is also useful for options like <code class="docutils literal notranslate"><span class="pre">-llibname</span></code> which is actually a positional argument that starts with a dash.</p> <p>So, generally, the problem is that you have two <code class="docutils literal notranslate"><span class="pre">cl::list</span></code> variables that interact in some way. To ensure the correct interaction, you can use the <code class="docutils literal notranslate"><span class="pre">cl::list::getPosition(optnum)</span></code> method. This method returns the absolute position (as found on the command line) of the <code class="docutils literal notranslate"><span class="pre">optnum</span></code> item in the <code class="docutils literal notranslate"><span class="pre">cl::list</span></code>.</p> <p>The idiom for usage is like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">static</span> <span class="n">cl</span><span class="o">::</span><span class="n">list</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Files</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">OneOrMore</span><span class="p">);</span> <span class="k">static</span> <span class="n">cl</span><span class="o">::</span><span class="n">list</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">></span> <span class="n">Libraries</span><span class="p">(</span><span class="s">"l"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">ZeroOrMore</span><span class="p">);</span> <span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span><span class="o">**</span><span class="n">argv</span><span class="p">)</span> <span class="p">{</span> <span class="c1">// ...</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">>::</span><span class="n">iterator</span> <span class="n">fileIt</span> <span class="o">=</span> <span class="n">Files</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span> <span class="n">std</span><span class="o">::</span><span class="n">vector</span><span class="o"><</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">>::</span><span class="n">iterator</span> <span class="n">libIt</span> <span class="o">=</span> <span class="n">Libraries</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span> <span class="kt">unsigned</span> <span class="n">libPos</span> <span class="o">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">filePos</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="k">while</span> <span class="p">(</span> <span class="mi">1</span> <span class="p">)</span> <span class="p">{</span> <span class="k">if</span> <span class="p">(</span> <span class="n">libIt</span> <span class="o">!=</span> <span class="n">Libraries</span><span class="p">.</span><span class="n">end</span><span class="p">()</span> <span class="p">)</span> <span class="n">libPos</span> <span class="o">=</span> <span class="n">Libraries</span><span class="p">.</span><span class="n">getPosition</span><span class="p">(</span> <span class="n">libIt</span> <span class="o">-</span> <span class="n">Libraries</span><span class="p">.</span><span class="n">begin</span><span class="p">()</span> <span class="p">);</span> <span class="k">else</span> <span class="n">libPos</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="k">if</span> <span class="p">(</span> <span class="n">fileIt</span> <span class="o">!=</span> <span class="n">Files</span><span class="p">.</span><span class="n">end</span><span class="p">()</span> <span class="p">)</span> <span class="n">filePos</span> <span class="o">=</span> <span class="n">Files</span><span class="p">.</span><span class="n">getPosition</span><span class="p">(</span> <span class="n">fileIt</span> <span class="o">-</span> <span class="n">Files</span><span class="p">.</span><span class="n">begin</span><span class="p">()</span> <span class="p">);</span> <span class="k">else</span> <span class="n">filePos</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span> <span class="k">if</span> <span class="p">(</span> <span class="n">filePos</span> <span class="o">!=</span> <span class="mi">0</span> <span class="o">&&</span> <span class="p">(</span><span class="n">libPos</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">filePos</span> <span class="o"><</span> <span class="n">libPos</span><span class="p">)</span> <span class="p">)</span> <span class="p">{</span> <span class="c1">// Source File Is next</span> <span class="o">++</span><span class="n">fileIt</span><span class="p">;</span> <span class="p">}</span> <span class="k">else</span> <span class="k">if</span> <span class="p">(</span> <span class="n">libPos</span> <span class="o">!=</span> <span class="mi">0</span> <span class="o">&&</span> <span class="p">(</span><span class="n">filePos</span> <span class="o">==</span> <span class="mi">0</span> <span class="o">||</span> <span class="n">libPos</span> <span class="o"><</span> <span class="n">filePos</span><span class="p">)</span> <span class="p">)</span> <span class="p">{</span> <span class="c1">// Library is next</span> <span class="o">++</span><span class="n">libIt</span><span class="p">;</span> <span class="p">}</span> <span class="k">else</span> <span class="k">break</span><span class="p">;</span> <span class="c1">// we're done with the list</span> <span class="p">}</span> <span class="p">}</span> </pre></div> </div> <p>Note that, for compatibility reasons, the <code class="docutils literal notranslate"><span class="pre">cl::opt</span></code> also supports an <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">getPosition()</span></code> option that will provide the absolute position of that option. You can apply the same approach as above with a <code class="docutils literal notranslate"><span class="pre">cl::opt</span></code> and a <code class="docutils literal notranslate"><span class="pre">cl::list</span></code> option as you can with two lists.</p> </div> <div class="section" id="the-cl-consumeafter-modifier"> <span id="this-section-for-more-information"></span><span id="cl-consumeafter"></span><span id="interpreter-style-options"></span><h4><a class="toc-backref" href="#id22">The <code class="docutils literal notranslate"><span class="pre">cl::ConsumeAfter</span></code> modifier</a><a class="headerlink" href="#the-cl-consumeafter-modifier" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::ConsumeAfter</span></code> <a class="reference internal" href="#formatting-option">formatting option</a> is used to construct programs that use “interpreter style” option processing. With this style of option processing, all arguments specified after the last positional argument are treated as special interpreter arguments that are not interpreted by the command line argument.</p> <p>As a concrete example, lets say we are developing a replacement for the standard Unix Bourne shell (<code class="docutils literal notranslate"><span class="pre">/bin/sh</span></code>). To run <code class="docutils literal notranslate"><span class="pre">/bin/sh</span></code>, first you specify options to the shell itself (like <code class="docutils literal notranslate"><span class="pre">-x</span></code> which turns on trace output), then you specify the name of the script to run, then you specify arguments to the script. These arguments to the script are parsed by the Bourne shell command line option processor, but are not interpreted as options to the shell itself. Using the CommandLine library, we would specify this as:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">Script</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Positional</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<input script>"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">init</span><span class="p">(</span><span class="s">"-"</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">list</span><span class="o"><</span><span class="n">string</span><span class="o">></span> <span class="n">Argv</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">ConsumeAfter</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"<program arguments>..."</span><span class="p">));</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Trace</span><span class="p">(</span><span class="s">"x"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Enable trace output"</span><span class="p">));</span> </pre></div> </div> <p>which automatically provides the help output:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">USAGE</span><span class="p">:</span> <span class="n">spiffysh</span> <span class="p">[</span><span class="n">options</span><span class="p">]</span> <span class="o"><</span><span class="nb">input</span> <span class="n">script</span><span class="o">></span> <span class="o"><</span><span class="n">program</span> <span class="n">arguments</span><span class="o">>...</span> <span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">-</span><span class="n">x</span> <span class="o">-</span> <span class="n">Enable</span> <span class="n">trace</span> <span class="n">output</span> </pre></div> </div> <p>At runtime, if we run our new shell replacement as <code class="docutils literal notranslate"><span class="pre">`spiffysh</span> <span class="pre">-x</span> <span class="pre">test.sh</span> <span class="pre">-a</span> <span class="pre">-x</span> <span class="pre">-y</span> <span class="pre">bar</span></code>’, the <code class="docutils literal notranslate"><span class="pre">Trace</span></code> variable will be set to true, the <code class="docutils literal notranslate"><span class="pre">Script</span></code> variable will be set to “<code class="docutils literal notranslate"><span class="pre">test.sh</span></code>”, and the <code class="docutils literal notranslate"><span class="pre">Argv</span></code> list will contain <code class="docutils literal notranslate"><span class="pre">["-a",</span> <span class="pre">"-x",</span> <span class="pre">"-y",</span> <span class="pre">"bar"]</span></code>, because they were specified after the last positional argument (which is the script name).</p> <p>There are several limitations to when <code class="docutils literal notranslate"><span class="pre">cl::ConsumeAfter</span></code> options can be specified. For example, only one <code class="docutils literal notranslate"><span class="pre">cl::ConsumeAfter</span></code> can be specified per program, there must be at least one <a class="reference internal" href="#positional-argument">positional argument</a> specified, there must not be any <a class="reference internal" href="#cl-list">cl::list</a> positional arguments, and the <code class="docutils literal notranslate"><span class="pre">cl::ConsumeAfter</span></code> option should be a <a class="reference internal" href="#cl-list">cl::list</a> option.</p> </div> </div> <div class="section" id="internal-vs-external-storage"> <span id="can-be-changed"></span><span id="id4"></span><h3><a class="toc-backref" href="#id23">Internal vs External Storage</a><a class="headerlink" href="#internal-vs-external-storage" title="Permalink to this headline">¶</a></h3> <p>By default, all command line options automatically hold the value that they parse from the command line. This is very convenient in the common case, especially when combined with the ability to define command line options in the files that use them. This is called the internal storage model.</p> <p>Sometimes, however, it is nice to separate the command line option processing code from the storage of the value parsed. For example, lets say that we have a ‘<code class="docutils literal notranslate"><span class="pre">-debug</span></code>’ option that we would like to use to enable debug information across the entire body of our program. In this case, the boolean value controlling the debug code should be globally accessible (in a header file, for example) yet the command line option processing code should not be exposed to all of these clients (requiring lots of .cpp files to <code class="docutils literal notranslate"><span class="pre">#include</span> <span class="pre">CommandLine.h</span></code>).</p> <p>To do this, set up your .h file with your option, like this for example:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="c1">// DebugFlag.h - Get access to the '-debug' command line option</span> <span class="c1">//</span> <span class="c1">// DebugFlag - This boolean is set to true if the '-debug' command line option</span> <span class="c1">// is specified. This should probably not be referenced directly, instead, use</span> <span class="c1">// the DEBUG macro below.</span> <span class="c1">//</span> <span class="k">extern</span> <span class="kt">bool</span> <span class="n">DebugFlag</span><span class="p">;</span> <span class="c1">// DEBUG macro - This macro should be used by code to emit debug information.</span> <span class="c1">// In the '-debug' option is specified on the command line, and if this is a</span> <span class="c1">// debug build, then the code specified as the option to the macro will be</span> <span class="c1">// executed. Otherwise it will not be.</span> <span class="cp">#ifdef NDEBUG</span> <span class="cp">#define LLVM_DEBUG(X)</span> <span class="cp">#else</span> <span class="cp">#define LLVM_DEBUG(X) do { if (DebugFlag) { X; } } while (0)</span> <span class="cp">#endif</span> </pre></div> </div> <p>This allows clients to blissfully use the <code class="docutils literal notranslate"><span class="pre">LLVM_DEBUG()</span></code> macro, or the <code class="docutils literal notranslate"><span class="pre">DebugFlag</span></code> explicitly if they want to. Now we just need to be able to set the <code class="docutils literal notranslate"><span class="pre">DebugFlag</span></code> boolean when the option is set. To do this, we pass an additional argument to our command line argument processor, and we specify where to fill in with the <a class="reference internal" href="#cl-location">cl::location</a> attribute:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">bool</span> <span class="n">DebugFlag</span><span class="p">;</span> <span class="c1">// the actual value</span> <span class="k">static</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="p">,</span> <span class="nb">true</span><span class="o">></span> <span class="c1">// The parser</span> <span class="n">Debug</span><span class="p">(</span><span class="s">"debug"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Enable debug output"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">Hidden</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">location</span><span class="p">(</span><span class="n">DebugFlag</span><span class="p">));</span> </pre></div> </div> <p>In the above example, we specify “<code class="docutils literal notranslate"><span class="pre">true</span></code>” as the second argument to the <a class="reference internal" href="#cl-opt">cl::opt</a> template, indicating that the template should not maintain a copy of the value itself. In addition to this, we specify the <a class="reference internal" href="#cl-location">cl::location</a> attribute, so that <code class="docutils literal notranslate"><span class="pre">DebugFlag</span></code> is automatically set.</p> </div> <div class="section" id="option-attributes"> <h3><a class="toc-backref" href="#id24">Option Attributes</a><a class="headerlink" href="#option-attributes" title="Permalink to this headline">¶</a></h3> <p>This section describes the basic attributes that you can specify on options.</p> <ul> <li><p class="first">The option name attribute (which is required for all options, except <a class="reference internal" href="#positional-options">positional options</a>) specifies what the option name is. This option is specified in simple double quotes:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">bool</span><span class="o">></span> <span class="n">Quiet</span><span class="p">(</span><span class="s">"quiet"</span><span class="p">);</span> </pre></div> </div> </li> </ul> <ul class="simple" id="cl-desc"> <li>The <strong>cl::desc</strong> attribute specifies a description for the option to be shown in the <code class="docutils literal notranslate"><span class="pre">-help</span></code> output for the program. This attribute supports multi-line descriptions with lines separated by ‘n’.</li> </ul> <ul class="simple" id="cl-value-desc"> <li>The <strong>cl::value_desc</strong> attribute specifies a string that can be used to fine tune the <code class="docutils literal notranslate"><span class="pre">-help</span></code> output for a command line option. Look <a class="reference internal" href="#here">here</a> for an example.</li> </ul> <ul id="cl-init"> <li><p class="first">The <strong>cl::init</strong> attribute specifies an initial value for a <a class="reference internal" href="#scalar">scalar</a> option. If this attribute is not specified then the command line option value defaults to the value created by the default constructor for the type.</p> <div class="admonition warning"> <p class="first admonition-title">Warning</p> <p class="last">If you specify both <strong>cl::init</strong> and <strong>cl::location</strong> for an option, you must specify <strong>cl::location</strong> first, so that when the command-line parser sees <strong>cl::init</strong>, it knows where to put the initial value. (You will get an error at runtime if you don’t put them in the right order.)</p> </div> </li> </ul> <ul class="simple" id="cl-location"> <li>The <strong>cl::location</strong> attribute where to store the value for a parsed command line option if using external storage. See the section on <a class="reference internal" href="#internal-vs-external-storage">Internal vs External Storage</a> for more information.</li> </ul> <ul class="simple" id="cl-aliasopt"> <li>The <strong>cl::aliasopt</strong> attribute specifies which option a <a class="reference internal" href="#cl-alias">cl::alias</a> option is an alias for.</li> </ul> <ul id="cl-values"> <li><p class="first">The <strong>cl::values</strong> attribute specifies the string-to-value mapping to be used by the generic parser. It takes a list of (option, value, description) triplets that specify the option name, the value mapped to, and the description shown in the <code class="docutils literal notranslate"><span class="pre">-help</span></code> for the tool. Because the generic parser is used most frequently with enum values, two macros are often useful:</p> <ol class="arabic simple"> <li>The <strong>clEnumVal</strong> macro is used as a nice simple way to specify a triplet for an enum. This macro automatically makes the option name be the same as the enum name. The first option to the macro is the enum, the second is the description for the command line option.</li> <li>The <strong>clEnumValN</strong> macro is used to specify macro options where the option name doesn’t equal the enum name. For this macro, the first argument is the enum value, the second is the flag name, and the second is the description.</li> </ol> <p>You will get a compile time error if you try to use cl::values with a parser that does not support it.</p> </li> </ul> <ul class="simple" id="cl-multi-val"> <li>The <strong>cl::multi_val</strong> attribute specifies that this option takes has multiple values (example: <code class="docutils literal notranslate"><span class="pre">-sectalign</span> <span class="pre">segname</span> <span class="pre">sectname</span> <span class="pre">sectvalue</span></code>). This attribute takes one unsigned argument - the number of values for the option. This attribute is valid only on <code class="docutils literal notranslate"><span class="pre">cl::list</span></code> options (and will fail with compile error if you try to use it with other option types). It is allowed to use all of the usual modifiers on multi-valued options (besides <code class="docutils literal notranslate"><span class="pre">cl::ValueDisallowed</span></code>, obviously).</li> </ul> <ul class="simple" id="cl-cat"> <li>The <strong>cl::cat</strong> attribute specifies the option category that the option belongs to. The category should be a <a class="reference internal" href="#cl-optioncategory">cl::OptionCategory</a> object.</li> </ul> </div> <div class="section" id="option-modifiers"> <h3><a class="toc-backref" href="#id25">Option Modifiers</a><a class="headerlink" href="#option-modifiers" title="Permalink to this headline">¶</a></h3> <p>Option modifiers are the flags and expressions that you pass into the constructors for <a class="reference internal" href="#cl-opt">cl::opt</a> and <a class="reference internal" href="#cl-list">cl::list</a>. These modifiers give you the ability to tweak how options are parsed and how <code class="docutils literal notranslate"><span class="pre">-help</span></code> output is generated to fit your application well.</p> <p>These options fall into five main categories:</p> <ol class="arabic simple"> <li>Hiding an option from <code class="docutils literal notranslate"><span class="pre">-help</span></code> output</li> <li>Controlling the number of occurrences required and allowed</li> <li>Controlling whether or not a value must be specified</li> <li>Controlling other formatting options</li> <li>Miscellaneous option modifiers</li> </ol> <p>It is not possible to specify two options from the same category (you’ll get a runtime error) to a single option, except for options in the miscellaneous category. The CommandLine library specifies defaults for all of these settings that are the most useful in practice and the most common, which mean that you usually shouldn’t have to worry about these.</p> <div class="section" id="hiding-an-option-from-help-output"> <h4><a class="toc-backref" href="#id26">Hiding an option from <code class="docutils literal notranslate"><span class="pre">-help</span></code> output</a><a class="headerlink" href="#hiding-an-option-from-help-output" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::NotHidden</span></code>, <code class="docutils literal notranslate"><span class="pre">cl::Hidden</span></code>, and <code class="docutils literal notranslate"><span class="pre">cl::ReallyHidden</span></code> modifiers are used to control whether or not an option appears in the <code class="docutils literal notranslate"><span class="pre">-help</span></code> and <code class="docutils literal notranslate"><span class="pre">-help-hidden</span></code> output for the compiled program:</p> <ul class="simple" id="cl-nothidden"> <li>The <strong>cl::NotHidden</strong> modifier (which is the default for <a class="reference internal" href="#cl-opt">cl::opt</a> and <a class="reference internal" href="#cl-list">cl::list</a> options) indicates the option is to appear in both help listings.</li> </ul> <ul class="simple" id="cl-hidden"> <li>The <strong>cl::Hidden</strong> modifier (which is the default for <a class="reference internal" href="#cl-alias">cl::alias</a> options) indicates that the option should not appear in the <code class="docutils literal notranslate"><span class="pre">-help</span></code> output, but should appear in the <code class="docutils literal notranslate"><span class="pre">-help-hidden</span></code> output.</li> </ul> <ul class="simple" id="cl-reallyhidden"> <li>The <strong>cl::ReallyHidden</strong> modifier indicates that the option should not appear in any help output.</li> </ul> </div> <div class="section" id="controlling-the-number-of-occurrences-required-and-allowed"> <h4><a class="toc-backref" href="#id27">Controlling the number of occurrences required and allowed</a><a class="headerlink" href="#controlling-the-number-of-occurrences-required-and-allowed" title="Permalink to this headline">¶</a></h4> <p>This group of options is used to control how many time an option is allowed (or required) to be specified on the command line of your program. Specifying a value for this setting allows the CommandLine library to do error checking for you.</p> <p>The allowed values for this option group are:</p> <ul class="simple" id="cl-optional"> <li>The <strong>cl::Optional</strong> modifier (which is the default for the <a class="reference internal" href="#cl-opt">cl::opt</a> and <a class="reference internal" href="#cl-alias">cl::alias</a> classes) indicates that your program will allow either zero or one occurrence of the option to be specified.</li> </ul> <ul class="simple" id="cl-zeroormore"> <li>The <strong>cl::ZeroOrMore</strong> modifier (which is the default for the <a class="reference internal" href="#cl-list">cl::list</a> class) indicates that your program will allow the option to be specified zero or more times.</li> </ul> <ul class="simple" id="cl-required"> <li>The <strong>cl::Required</strong> modifier indicates that the specified option must be specified exactly one time.</li> </ul> <ul class="simple" id="cl-oneormore"> <li>The <strong>cl::OneOrMore</strong> modifier indicates that the option must be specified at least one time.</li> <li>The <strong>cl::ConsumeAfter</strong> modifier is described in the <a class="reference internal" href="#positional-arguments-section">Positional arguments section</a>.</li> </ul> <p>If an option is not specified, then the value of the option is equal to the value specified by the <a class="reference internal" href="#cl-init">cl::init</a> attribute. If the <code class="docutils literal notranslate"><span class="pre">cl::init</span></code> attribute is not specified, the option value is initialized with the default constructor for the data type.</p> <p>If an option is specified multiple times for an option of the <a class="reference internal" href="#cl-opt">cl::opt</a> class, only the last value will be retained.</p> </div> <div class="section" id="controlling-whether-or-not-a-value-must-be-specified"> <h4><a class="toc-backref" href="#id28">Controlling whether or not a value must be specified</a><a class="headerlink" href="#controlling-whether-or-not-a-value-must-be-specified" title="Permalink to this headline">¶</a></h4> <p>This group of options is used to control whether or not the option allows a value to be present. In the case of the CommandLine library, a value is either specified with an equal sign (e.g. ‘<code class="docutils literal notranslate"><span class="pre">-index-depth=17</span></code>’) or as a trailing string (e.g. ‘<code class="docutils literal notranslate"><span class="pre">-o</span> <span class="pre">a.out</span></code>’).</p> <p>The allowed values for this option group are:</p> <ul class="simple" id="cl-valueoptional"> <li>The <strong>cl::ValueOptional</strong> modifier (which is the default for <code class="docutils literal notranslate"><span class="pre">bool</span></code> typed options) specifies that it is acceptable to have a value, or not. A boolean argument can be enabled just by appearing on the command line, or it can have an explicit ‘<code class="docutils literal notranslate"><span class="pre">-foo=true</span></code>’. If an option is specified with this mode, it is illegal for the value to be provided without the equal sign. Therefore ‘<code class="docutils literal notranslate"><span class="pre">-foo</span> <span class="pre">true</span></code>’ is illegal. To get this behavior, you must use the <a class="reference internal" href="#cl-valuerequired">cl::ValueRequired</a> modifier.</li> </ul> <ul class="simple" id="cl-valuerequired"> <li>The <strong>cl::ValueRequired</strong> modifier (which is the default for all other types except for <a class="reference internal" href="#unnamed-alternatives-using-the-generic-parser">unnamed alternatives using the generic parser</a>) specifies that a value must be provided. This mode informs the command line library that if an option is not provides with an equal sign, that the next argument provided must be the value. This allows things like ‘<code class="docutils literal notranslate"><span class="pre">-o</span> <span class="pre">a.out</span></code>’ to work.</li> </ul> <ul class="simple" id="cl-valuedisallowed"> <li>The <strong>cl::ValueDisallowed</strong> modifier (which is the default for <a class="reference internal" href="#unnamed-alternatives-using-the-generic-parser">unnamed alternatives using the generic parser</a>) indicates that it is a runtime error for the user to specify a value. This can be provided to disallow users from providing options to boolean options (like ‘<code class="docutils literal notranslate"><span class="pre">-foo=true</span></code>’).</li> </ul> <p>In general, the default values for this option group work just like you would want them to. As mentioned above, you can specify the <a class="reference internal" href="#cl-valuedisallowed">cl::ValueDisallowed</a> modifier to a boolean argument to restrict your command line parser. These options are mostly useful when <a class="reference internal" href="#extending-the-library">extending the library</a>.</p> </div> <div class="section" id="controlling-other-formatting-options"> <span id="formatting-option"></span><h4><a class="toc-backref" href="#id29">Controlling other formatting options</a><a class="headerlink" href="#controlling-other-formatting-options" title="Permalink to this headline">¶</a></h4> <p>The formatting option group is used to specify that the command line option has special abilities and is otherwise different from other command line arguments. As usual, you can only specify one of these arguments at most.</p> <ul class="simple" id="cl-normalformatting"> <li>The <strong>cl::NormalFormatting</strong> modifier (which is the default all options) specifies that this option is “normal”.</li> </ul> <ul class="simple" id="cl-positional"> <li>The <strong>cl::Positional</strong> modifier specifies that this is a positional argument that does not have a command line option associated with it. See the <a class="reference internal" href="#positional-arguments">Positional Arguments</a> section for more information.</li> <li>The <strong>cl::ConsumeAfter</strong> modifier specifies that this option is used to capture “interpreter style” arguments. See <a class="reference internal" href="#this-section-for-more-information">this section for more information</a>.</li> </ul> <span id="prefix"></span><ul class="simple" id="cl-prefix"> <li>The <strong>cl::Prefix</strong> modifier specifies that this option prefixes its value. With ‘Prefix’ options, the equal sign does not separate the value from the option name specified. Instead, the value is everything after the prefix, including any equal sign if present. This is useful for processing odd arguments like <code class="docutils literal notranslate"><span class="pre">-lmalloc</span></code> and <code class="docutils literal notranslate"><span class="pre">-L/usr/lib</span></code> in a linker tool or <code class="docutils literal notranslate"><span class="pre">-DNAME=value</span></code> in a compiler tool. Here, the ‘<code class="docutils literal notranslate"><span class="pre">l</span></code>’, ‘<code class="docutils literal notranslate"><span class="pre">D</span></code>’ and ‘<code class="docutils literal notranslate"><span class="pre">L</span></code>’ options are normal string (or list) options, that have the <strong>cl::Prefix</strong> modifier added to allow the CommandLine library to recognize them. Note that <strong>cl::Prefix</strong> options must not have the <strong>cl::ValueDisallowed</strong> modifier specified.</li> </ul> <span id="grouping"></span><ul class="simple" id="cl-grouping"> <li>The <strong>cl::Grouping</strong> modifier is used to implement Unix-style tools (like <code class="docutils literal notranslate"><span class="pre">ls</span></code>) that have lots of single letter arguments, but only require a single dash. For example, the ‘<code class="docutils literal notranslate"><span class="pre">ls</span> <span class="pre">-labF</span></code>’ command actually enables four different options, all of which are single letters. Note that <strong>cl::Grouping</strong> options cannot have values.</li> </ul> <p>The CommandLine library does not restrict how you use the <strong>cl::Prefix</strong> or <strong>cl::Grouping</strong> modifiers, but it is possible to specify ambiguous argument settings. Thus, it is possible to have multiple letter options that are prefix or grouping options, and they will still work as designed.</p> <p>To do this, the CommandLine library uses a greedy algorithm to parse the input option into (potentially multiple) prefix and grouping options. The strategy basically looks like this:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span>parse(string OrigInput) { 1. string input = OrigInput; 2. if (isOption(input)) return getOption(input).parse(); // Normal option 3. while (!isOption(input) && !input.empty()) input.pop_back(); // Remove the last letter 4. if (input.empty()) return error(); // No matching option 5. if (getOption(input).isPrefix()) return getOption(input).parse(input); 6. while (!input.empty()) { // Must be grouping options getOption(input).parse(); OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length()); input = OrigInput; while (!isOption(input) && !input.empty()) input.pop_back(); } 7. if (!OrigInput.empty()) error(); } </pre></div> </div> </div> <div class="section" id="miscellaneous-option-modifiers"> <h4><a class="toc-backref" href="#id30">Miscellaneous option modifiers</a><a class="headerlink" href="#miscellaneous-option-modifiers" title="Permalink to this headline">¶</a></h4> <p>The miscellaneous option modifiers are the only flags where you can specify more than one flag from the set: they are not mutually exclusive. These flags specify boolean properties that modify the option.</p> <ul class="simple" id="cl-commaseparated"> <li>The <strong>cl::CommaSeparated</strong> modifier indicates that any commas specified for an option’s value should be used to split the value up into multiple values for the option. For example, these two options are equivalent when <code class="docutils literal notranslate"><span class="pre">cl::CommaSeparated</span></code> is specified: “<code class="docutils literal notranslate"><span class="pre">-foo=a</span> <span class="pre">-foo=b</span> <span class="pre">-foo=c</span></code>” and “<code class="docutils literal notranslate"><span class="pre">-foo=a,b,c</span></code>”. This option only makes sense to be used in a case where the option is allowed to accept one or more values (i.e. it is a <a class="reference internal" href="#cl-list">cl::list</a> option).</li> </ul> <ul class="simple" id="cl-positionaleatsargs"> <li>The <strong>cl::PositionalEatsArgs</strong> modifier (which only applies to positional arguments, and only makes sense for lists) indicates that positional argument should consume any strings after it (including strings that start with a “-“) up until another recognized positional argument. For example, if you have two “eating” positional arguments, “<code class="docutils literal notranslate"><span class="pre">pos1</span></code>” and “<code class="docutils literal notranslate"><span class="pre">pos2</span></code>”, the string “<code class="docutils literal notranslate"><span class="pre">-pos1</span> <span class="pre">-foo</span> <span class="pre">-bar</span> <span class="pre">baz</span> <span class="pre">-pos2</span> <span class="pre">-bork</span></code>” would cause the “<code class="docutils literal notranslate"><span class="pre">-foo</span> <span class="pre">-bar</span> <span class="pre">-baz</span></code>” strings to be applied to the “<code class="docutils literal notranslate"><span class="pre">-pos1</span></code>” option and the “<code class="docutils literal notranslate"><span class="pre">-bork</span></code>” string to be applied to the “<code class="docutils literal notranslate"><span class="pre">-pos2</span></code>” option.</li> </ul> <ul class="simple" id="cl-sink"> <li>The <strong>cl::Sink</strong> modifier is used to handle unknown options. If there is at least one option with <code class="docutils literal notranslate"><span class="pre">cl::Sink</span></code> modifier specified, the parser passes unrecognized option strings to it as values instead of signaling an error. As with <code class="docutils literal notranslate"><span class="pre">cl::CommaSeparated</span></code>, this modifier only makes sense with a <a class="reference internal" href="#cl-list">cl::list</a> option.</li> </ul> <p>So far, these are the only three miscellaneous option modifiers.</p> </div> <div class="section" id="response-files"> <span id="id5"></span><h4><a class="toc-backref" href="#id31">Response files</a><a class="headerlink" href="#response-files" title="Permalink to this headline">¶</a></h4> <p>Some systems, such as certain variants of Microsoft Windows and some older Unices have a relatively low limit on command-line length. It is therefore customary to use the so-called ‘response files’ to circumvent this restriction. These files are mentioned on the command-line (using the “@file”) syntax. The program reads these files and inserts the contents into argv, thereby working around the command-line length limits.</p> </div> </div> <div class="section" id="top-level-classes-and-functions"> <h3><a class="toc-backref" href="#id32">Top-Level Classes and Functions</a><a class="headerlink" href="#top-level-classes-and-functions" title="Permalink to this headline">¶</a></h3> <p>Despite all of the built-in flexibility, the CommandLine option library really only consists of one function <a class="reference internal" href="#cl-parsecommandlineoptions">cl::ParseCommandLineOptions</a>) and three main classes: <a class="reference internal" href="#cl-opt">cl::opt</a>, <a class="reference internal" href="#cl-list">cl::list</a>, and <a class="reference internal" href="#cl-alias">cl::alias</a>. This section describes these three classes in detail.</p> <div class="section" id="the-cl-getregisteredoptions-function"> <span id="cl-getregisteredoptions"></span><h4><a class="toc-backref" href="#id33">The <code class="docutils literal notranslate"><span class="pre">cl::getRegisteredOptions</span></code> function</a><a class="headerlink" href="#the-cl-getregisteredoptions-function" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::getRegisteredOptions</span></code> function is designed to give a programmer access to declared non-positional command line options so that how they appear in <code class="docutils literal notranslate"><span class="pre">-help</span></code> can be modified prior to calling <a class="reference internal" href="#cl-parsecommandlineoptions">cl::ParseCommandLineOptions</a>. Note this method should not be called during any static initialisation because it cannot be guaranteed that all options will have been initialised. Hence it should be called from <code class="docutils literal notranslate"><span class="pre">main</span></code>.</p> <p>This function can be used to gain access to options declared in libraries that the tool writter may not have direct access to.</p> <p>The function retrieves a <a class="reference internal" href="ProgrammersManual.html#dss-stringmap"><span class="std std-ref">StringMap</span></a> that maps the option string (e.g. <code class="docutils literal notranslate"><span class="pre">-help</span></code>) to an <code class="docutils literal notranslate"><span class="pre">Option*</span></code>.</p> <p>Here is an example of how the function could be used:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">using</span> <span class="k">namespace</span> <span class="n">llvm</span><span class="p">;</span> <span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span> <span class="o">**</span><span class="n">argv</span><span class="p">)</span> <span class="p">{</span> <span class="n">cl</span><span class="o">::</span><span class="n">OptionCategory</span> <span class="n">AnotherCategory</span><span class="p">(</span><span class="s">"Some options"</span><span class="p">);</span> <span class="n">StringMap</span><span class="o"><</span><span class="n">cl</span><span class="o">::</span><span class="n">Option</span><span class="o">*></span> <span class="o">&</span><span class="n">Map</span> <span class="o">=</span> <span class="n">cl</span><span class="o">::</span><span class="n">getRegisteredOptions</span><span class="p">();</span> <span class="c1">//Unhide useful option and put it in a different category</span> <span class="n">assert</span><span class="p">(</span><span class="n">Map</span><span class="p">.</span><span class="n">count</span><span class="p">(</span><span class="s">"print-all-options"</span><span class="p">)</span> <span class="o">></span> <span class="mi">0</span><span class="p">);</span> <span class="n">Map</span><span class="p">[</span><span class="s">"print-all-options"</span><span class="p">]</span><span class="o">-></span><span class="n">setHiddenFlag</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">NotHidden</span><span class="p">);</span> <span class="n">Map</span><span class="p">[</span><span class="s">"print-all-options"</span><span class="p">]</span><span class="o">-></span><span class="n">setCategory</span><span class="p">(</span><span class="n">AnotherCategory</span><span class="p">);</span> <span class="c1">//Hide an option we don't want to see</span> <span class="n">assert</span><span class="p">(</span><span class="n">Map</span><span class="p">.</span><span class="n">count</span><span class="p">(</span><span class="s">"enable-no-infs-fp-math"</span><span class="p">)</span> <span class="o">></span> <span class="mi">0</span><span class="p">);</span> <span class="n">Map</span><span class="p">[</span><span class="s">"enable-no-infs-fp-math"</span><span class="p">]</span><span class="o">-></span><span class="n">setHiddenFlag</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Hidden</span><span class="p">);</span> <span class="c1">//Change --version to --show-version</span> <span class="n">assert</span><span class="p">(</span><span class="n">Map</span><span class="p">.</span><span class="n">count</span><span class="p">(</span><span class="s">"version"</span><span class="p">)</span> <span class="o">></span> <span class="mi">0</span><span class="p">);</span> <span class="n">Map</span><span class="p">[</span><span class="s">"version"</span><span class="p">]</span><span class="o">-></span><span class="n">setArgStr</span><span class="p">(</span><span class="s">"show-version"</span><span class="p">);</span> <span class="c1">//Change --help description</span> <span class="n">assert</span><span class="p">(</span><span class="n">Map</span><span class="p">.</span><span class="n">count</span><span class="p">(</span><span class="s">"help"</span><span class="p">)</span> <span class="o">></span> <span class="mi">0</span><span class="p">);</span> <span class="n">Map</span><span class="p">[</span><span class="s">"help"</span><span class="p">]</span><span class="o">-></span><span class="n">setDescription</span><span class="p">(</span><span class="s">"Shows help"</span><span class="p">);</span> <span class="n">cl</span><span class="o">::</span><span class="n">ParseCommandLineOptions</span><span class="p">(</span><span class="n">argc</span><span class="p">,</span> <span class="n">argv</span><span class="p">,</span> <span class="s">"This is a small program to demo the LLVM CommandLine API"</span><span class="p">);</span> <span class="p">...</span> <span class="p">}</span> </pre></div> </div> </div> <div class="section" id="the-cl-parsecommandlineoptions-function"> <span id="cl-parsecommandlineoptions"></span><h4><a class="toc-backref" href="#id34">The <code class="docutils literal notranslate"><span class="pre">cl::ParseCommandLineOptions</span></code> function</a><a class="headerlink" href="#the-cl-parsecommandlineoptions-function" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::ParseCommandLineOptions</span></code> function is designed to be called directly from <code class="docutils literal notranslate"><span class="pre">main</span></code>, and is used to fill in the values of all of the command line option variables once <code class="docutils literal notranslate"><span class="pre">argc</span></code> and <code class="docutils literal notranslate"><span class="pre">argv</span></code> are available.</p> <p>The <code class="docutils literal notranslate"><span class="pre">cl::ParseCommandLineOptions</span></code> function requires two parameters (<code class="docutils literal notranslate"><span class="pre">argc</span></code> and <code class="docutils literal notranslate"><span class="pre">argv</span></code>), but may also take an optional third parameter which holds <a class="reference internal" href="#additional-extra-text">additional extra text</a> to emit when the <code class="docutils literal notranslate"><span class="pre">-help</span></code> option is invoked.</p> </div> <div class="section" id="the-cl-parseenvironmentoptions-function"> <span id="cl-parseenvironmentoptions"></span><h4><a class="toc-backref" href="#id35">The <code class="docutils literal notranslate"><span class="pre">cl::ParseEnvironmentOptions</span></code> function</a><a class="headerlink" href="#the-cl-parseenvironmentoptions-function" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::ParseEnvironmentOptions</span></code> function has mostly the same effects as <a class="reference internal" href="#cl-parsecommandlineoptions">cl::ParseCommandLineOptions</a>, except that it is designed to take values for options from an environment variable, for those cases in which reading the command line is not convenient or desired. It fills in the values of all the command line option variables just like <a class="reference internal" href="#cl-parsecommandlineoptions">cl::ParseCommandLineOptions</a> does.</p> <p>It takes four parameters: the name of the program (since <code class="docutils literal notranslate"><span class="pre">argv</span></code> may not be available, it can’t just look in <code class="docutils literal notranslate"><span class="pre">argv[0]</span></code>), the name of the environment variable to examine, and the optional <a class="reference internal" href="#additional-extra-text">additional extra text</a> to emit when the <code class="docutils literal notranslate"><span class="pre">-help</span></code> option is invoked.</p> <p><code class="docutils literal notranslate"><span class="pre">cl::ParseEnvironmentOptions</span></code> will break the environment variable’s value up into words and then process them using <a class="reference internal" href="#cl-parsecommandlineoptions">cl::ParseCommandLineOptions</a>. <strong>Note:</strong> Currently <code class="docutils literal notranslate"><span class="pre">cl::ParseEnvironmentOptions</span></code> does not support quoting, so an environment variable containing <code class="docutils literal notranslate"><span class="pre">-option</span> <span class="pre">"foo</span> <span class="pre">bar"</span></code> will be parsed as three words, <code class="docutils literal notranslate"><span class="pre">-option</span></code>, <code class="docutils literal notranslate"><span class="pre">"foo</span></code>, and <code class="docutils literal notranslate"><span class="pre">bar"</span></code>, which is different from what you would get from the shell with the same input.</p> </div> <div class="section" id="the-cl-setversionprinter-function"> <h4><a class="toc-backref" href="#id36">The <code class="docutils literal notranslate"><span class="pre">cl::SetVersionPrinter</span></code> function</a><a class="headerlink" href="#the-cl-setversionprinter-function" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::SetVersionPrinter</span></code> function is designed to be called directly from <code class="docutils literal notranslate"><span class="pre">main</span></code> and <em>before</em> <code class="docutils literal notranslate"><span class="pre">cl::ParseCommandLineOptions</span></code>. Its use is optional. It simply arranges for a function to be called in response to the <code class="docutils literal notranslate"><span class="pre">--version</span></code> option instead of having the <code class="docutils literal notranslate"><span class="pre">CommandLine</span></code> library print out the usual version string for LLVM. This is useful for programs that are not part of LLVM but wish to use the <code class="docutils literal notranslate"><span class="pre">CommandLine</span></code> facilities. Such programs should just define a small function that takes no arguments and returns <code class="docutils literal notranslate"><span class="pre">void</span></code> and that prints out whatever version information is appropriate for the program. Pass the address of that function to <code class="docutils literal notranslate"><span class="pre">cl::SetVersionPrinter</span></code> to arrange for it to be called when the <code class="docutils literal notranslate"><span class="pre">--version</span></code> option is given by the user.</p> </div> <div class="section" id="the-cl-opt-class"> <span id="scalar"></span><span id="cl-opt"></span><h4><a class="toc-backref" href="#id37">The <code class="docutils literal notranslate"><span class="pre">cl::opt</span></code> class</a><a class="headerlink" href="#the-cl-opt-class" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::opt</span></code> class is the class used to represent scalar command line options, and is the one used most of the time. It is a templated class which can take up to three arguments (all except for the first have default values though):</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">namespace</span> <span class="n">cl</span> <span class="p">{</span> <span class="k">template</span> <span class="o"><</span><span class="k">class</span> <span class="nc">DataType</span><span class="p">,</span> <span class="kt">bool</span> <span class="n">ExternalStorage</span> <span class="o">=</span> <span class="nb">false</span><span class="p">,</span> <span class="k">class</span> <span class="nc">ParserClass</span> <span class="o">=</span> <span class="n">parser</span><span class="o"><</span><span class="n">DataType</span><span class="o">></span> <span class="o">></span> <span class="k">class</span> <span class="nc">opt</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>The first template argument specifies what underlying data type the command line argument is, and is used to select a default parser implementation. The second template argument is used to specify whether the option should contain the storage for the option (the default) or whether external storage should be used to contain the value parsed for the option (see <a class="reference internal" href="#internal-vs-external-storage">Internal vs External Storage</a> for more information).</p> <p>The third template argument specifies which parser to use. The default value selects an instantiation of the <code class="docutils literal notranslate"><span class="pre">parser</span></code> class based on the underlying data type of the option. In general, this default works well for most applications, so this option is only used when using a <a class="reference internal" href="#custom-parser">custom parser</a>.</p> </div> <div class="section" id="the-cl-list-class"> <span id="cl-list"></span><span id="lists-of-arguments"></span><h4><a class="toc-backref" href="#id38">The <code class="docutils literal notranslate"><span class="pre">cl::list</span></code> class</a><a class="headerlink" href="#the-cl-list-class" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::list</span></code> class is the class used to represent a list of command line options. It too is a templated class which can take up to three arguments:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">namespace</span> <span class="n">cl</span> <span class="p">{</span> <span class="k">template</span> <span class="o"><</span><span class="k">class</span> <span class="nc">DataType</span><span class="p">,</span> <span class="k">class</span> <span class="nc">Storage</span> <span class="o">=</span> <span class="kt">bool</span><span class="p">,</span> <span class="k">class</span> <span class="nc">ParserClass</span> <span class="o">=</span> <span class="n">parser</span><span class="o"><</span><span class="n">DataType</span><span class="o">></span> <span class="o">></span> <span class="k">class</span> <span class="nc">list</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>This class works the exact same as the <a class="reference internal" href="#cl-opt">cl::opt</a> class, except that the second argument is the <strong>type</strong> of the external storage, not a boolean value. For this class, the marker type ‘<code class="docutils literal notranslate"><span class="pre">bool</span></code>’ is used to indicate that internal storage should be used.</p> </div> <div class="section" id="the-cl-bits-class"> <span id="cl-bits"></span><h4><a class="toc-backref" href="#id39">The <code class="docutils literal notranslate"><span class="pre">cl::bits</span></code> class</a><a class="headerlink" href="#the-cl-bits-class" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::bits</span></code> class is the class used to represent a list of command line options in the form of a bit vector. It is also a templated class which can take up to three arguments:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">namespace</span> <span class="n">cl</span> <span class="p">{</span> <span class="k">template</span> <span class="o"><</span><span class="k">class</span> <span class="nc">DataType</span><span class="p">,</span> <span class="k">class</span> <span class="nc">Storage</span> <span class="o">=</span> <span class="kt">bool</span><span class="p">,</span> <span class="k">class</span> <span class="nc">ParserClass</span> <span class="o">=</span> <span class="n">parser</span><span class="o"><</span><span class="n">DataType</span><span class="o">></span> <span class="o">></span> <span class="k">class</span> <span class="nc">bits</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>This class works the exact same as the <a class="reference internal" href="#cl-list">cl::list</a> class, except that the second argument must be of <strong>type</strong> <code class="docutils literal notranslate"><span class="pre">unsigned</span></code> if external storage is used.</p> </div> <div class="section" id="the-cl-alias-class"> <span id="cl-alias"></span><h4><a class="toc-backref" href="#id40">The <code class="docutils literal notranslate"><span class="pre">cl::alias</span></code> class</a><a class="headerlink" href="#the-cl-alias-class" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::alias</span></code> class is a nontemplated class that is used to form aliases for other arguments.</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">namespace</span> <span class="n">cl</span> <span class="p">{</span> <span class="k">class</span> <span class="nc">alias</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>The <a class="reference internal" href="#cl-aliasopt">cl::aliasopt</a> attribute should be used to specify which option this is an alias for. Alias arguments default to being <a class="reference internal" href="#cl-hidden">cl::Hidden</a>, and use the aliased options parser to do the conversion from string to data.</p> </div> <div class="section" id="the-cl-extrahelp-class"> <span id="cl-extrahelp"></span><h4><a class="toc-backref" href="#id41">The <code class="docutils literal notranslate"><span class="pre">cl::extrahelp</span></code> class</a><a class="headerlink" href="#the-cl-extrahelp-class" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::extrahelp</span></code> class is a nontemplated class that allows extra help text to be printed out for the <code class="docutils literal notranslate"><span class="pre">-help</span></code> option.</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">namespace</span> <span class="n">cl</span> <span class="p">{</span> <span class="k">struct</span> <span class="n">extrahelp</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>To use the extrahelp, simply construct one with a <code class="docutils literal notranslate"><span class="pre">const</span> <span class="pre">char*</span></code> parameter to the constructor. The text passed to the constructor will be printed at the bottom of the help message, verbatim. Note that multiple <code class="docutils literal notranslate"><span class="pre">cl::extrahelp</span></code> <strong>can</strong> be used, but this practice is discouraged. If your tool needs to print additional help information, put all that help into a single <code class="docutils literal notranslate"><span class="pre">cl::extrahelp</span></code> instance.</p> <p>For example:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">cl</span><span class="o">::</span><span class="n">extrahelp</span><span class="p">(</span><span class="s">"</span><span class="se">\n</span><span class="s">ADDITIONAL HELP:</span><span class="se">\n\n</span><span class="s"> This is the extra help</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span> </pre></div> </div> </div> <div class="section" id="the-cl-optioncategory-class"> <span id="cl-optioncategory"></span><h4><a class="toc-backref" href="#id42">The <code class="docutils literal notranslate"><span class="pre">cl::OptionCategory</span></code> class</a><a class="headerlink" href="#the-cl-optioncategory-class" title="Permalink to this headline">¶</a></h4> <p>The <code class="docutils literal notranslate"><span class="pre">cl::OptionCategory</span></code> class is a simple class for declaring option categories.</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">namespace</span> <span class="n">cl</span> <span class="p">{</span> <span class="k">class</span> <span class="nc">OptionCategory</span><span class="p">;</span> <span class="p">}</span> </pre></div> </div> <p>An option category must have a name and optionally a description which are passed to the constructor as <code class="docutils literal notranslate"><span class="pre">const</span> <span class="pre">char*</span></code>.</p> <p>Note that declaring an option category and associating it with an option before parsing options (e.g. statically) will change the output of <code class="docutils literal notranslate"><span class="pre">-help</span></code> from uncategorized to categorized. If an option category is declared but not associated with an option then it will be hidden from the output of <code class="docutils literal notranslate"><span class="pre">-help</span></code> but will be shown in the output of <code class="docutils literal notranslate"><span class="pre">-help-hidden</span></code>.</p> </div> </div> <div class="section" id="builtin-parsers"> <span id="discussed-previously"></span><span id="different-parser"></span><h3><a class="toc-backref" href="#id43">Builtin parsers</a><a class="headerlink" href="#builtin-parsers" title="Permalink to this headline">¶</a></h3> <p>Parsers control how the string value taken from the command line is translated into a typed value, suitable for use in a C++ program. By default, the CommandLine library uses an instance of <code class="docutils literal notranslate"><span class="pre">parser<type></span></code> if the command line option specifies that it uses values of type ‘<code class="docutils literal notranslate"><span class="pre">type</span></code>’. Because of this, custom option processing is specified with specializations of the ‘<code class="docutils literal notranslate"><span class="pre">parser</span></code>’ class.</p> <p>The CommandLine library provides the following builtin parser specializations, which are sufficient for most applications. It can, however, also be extended to work with new data types and new ways of interpreting the same data. See the <a class="reference internal" href="#writing-a-custom-parser">Writing a Custom Parser</a> for more details on this type of library extension.</p> <span id="enums"></span><ul class="simple" id="cl-parser"> <li>The generic <code class="docutils literal notranslate"><span class="pre">parser<t></span></code> parser can be used to map strings values to any data type, through the use of the <a class="reference internal" href="#cl-values">cl::values</a> property, which specifies the mapping information. The most common use of this parser is for parsing enum values, which allows you to use the CommandLine library for all of the error checking to make sure that only valid enum values are specified (as opposed to accepting arbitrary strings). Despite this, however, the generic parser class can be used for any data type.</li> </ul> <span id="boolean-flags"></span><ul class="simple" id="bool-parser"> <li>The <strong>parser<bool> specialization</strong> is used to convert boolean strings to a boolean value. Currently accepted strings are “<code class="docutils literal notranslate"><span class="pre">true</span></code>”, “<code class="docutils literal notranslate"><span class="pre">TRUE</span></code>”, “<code class="docutils literal notranslate"><span class="pre">True</span></code>”, “<code class="docutils literal notranslate"><span class="pre">1</span></code>”, “<code class="docutils literal notranslate"><span class="pre">false</span></code>”, “<code class="docutils literal notranslate"><span class="pre">FALSE</span></code>”, “<code class="docutils literal notranslate"><span class="pre">False</span></code>”, and “<code class="docutils literal notranslate"><span class="pre">0</span></code>”.</li> <li>The <strong>parser<boolOrDefault> specialization</strong> is used for cases where the value is boolean, but we also need to know whether the option was specified at all. boolOrDefault is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. This parser accepts the same strings as <strong>``parser<bool>``</strong>.</li> </ul> <ul class="simple" id="strings"> <li>The <strong>parser<string> specialization</strong> simply stores the parsed string into the string value specified. No conversion or modification of the data is performed.</li> </ul> <span id="integers"></span><ul class="simple" id="int"> <li>The <strong>parser<int> specialization</strong> uses the C <code class="docutils literal notranslate"><span class="pre">strtol</span></code> function to parse the string input. As such, it will accept a decimal number (with an optional ‘+’ or ‘-‘ prefix) which must start with a non-zero digit. It accepts octal numbers, which are identified with a ‘<code class="docutils literal notranslate"><span class="pre">0</span></code>’ prefix digit, and hexadecimal numbers with a prefix of ‘<code class="docutils literal notranslate"><span class="pre">0x</span></code>’ or ‘<code class="docutils literal notranslate"><span class="pre">0X</span></code>’.</li> </ul> <span id="float"></span><span id="doubles"></span><ul class="simple" id="double"> <li>The <strong>parser<double></strong> and <strong>parser<float> specializations</strong> use the standard C <code class="docutils literal notranslate"><span class="pre">strtod</span></code> function to convert floating point strings into floating point values. As such, a broad range of string formats is supported, including exponential notation (ex: <code class="docutils literal notranslate"><span class="pre">1.7e15</span></code>) and properly supports locales.</li> </ul> </div> </div> <div class="section" id="extending-the-library"> <span id="extension-guide"></span><span id="id6"></span><h2><a class="toc-backref" href="#id44">Extension Guide</a><a class="headerlink" href="#extending-the-library" title="Permalink to this headline">¶</a></h2> <p>Although the CommandLine library has a lot of functionality built into it already (as discussed previously), one of its true strengths lie in its extensibility. This section discusses how the CommandLine library works under the covers and illustrates how to do some simple, common, extensions.</p> <div class="section" id="writing-a-custom-parser"> <span id="custom-parser"></span><span id="custom-parsers"></span><span id="id7"></span><h3><a class="toc-backref" href="#id45">Writing a custom parser</a><a class="headerlink" href="#writing-a-custom-parser" title="Permalink to this headline">¶</a></h3> <p>One of the simplest and most common extensions is the use of a custom parser. As <a class="reference internal" href="#discussed-previously">discussed previously</a>, parsers are the portion of the CommandLine library that turns string input from the user into a particular parsed data type, validating the input in the process.</p> <p>There are two ways to use a new parser:</p> <ol class="arabic"> <li><p class="first">Specialize the <a class="reference internal" href="#cl-parser">cl::parser</a> template for your custom data type.</p> <p>This approach has the advantage that users of your custom data type will automatically use your custom parser whenever they define an option with a value type of your data type. The disadvantage of this approach is that it doesn’t work if your fundamental data type is something that is already supported.</p> </li> <li><p class="first">Write an independent class, using it explicitly from options that need it.</p> <p>This approach works well in situations where you would line to parse an option using special syntax for a not-very-special data-type. The drawback of this approach is that users of your parser have to be aware that they are using your parser instead of the builtin ones.</p> </li> </ol> <p>To guide the discussion, we will discuss a custom parser that accepts file sizes, specified with an optional unit after the numeric size. For example, we would like to parse “102kb”, “41M”, “1G” into the appropriate integer value. In this case, the underlying data type we want to parse into is ‘<code class="docutils literal notranslate"><span class="pre">unsigned</span></code>’. We choose approach #2 above because we don’t want to make this the default for all <code class="docutils literal notranslate"><span class="pre">unsigned</span></code> options.</p> <p>To start out, we declare our new <code class="docutils literal notranslate"><span class="pre">FileSizeParser</span></code> class:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span> <span class="nl">FileSizeParser</span> <span class="p">:</span> <span class="k">public</span> <span class="n">cl</span><span class="o">::</span><span class="n">parser</span><span class="o"><</span><span class="kt">unsigned</span><span class="o">></span> <span class="p">{</span> <span class="c1">// parse - Return true on error.</span> <span class="kt">bool</span> <span class="n">parse</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Option</span> <span class="o">&</span><span class="n">O</span><span class="p">,</span> <span class="n">StringRef</span> <span class="n">ArgName</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">ArgValue</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="o">&</span><span class="n">Val</span><span class="p">);</span> <span class="p">};</span> </pre></div> </div> <p>Our new class inherits from the <code class="docutils literal notranslate"><span class="pre">cl::parser</span></code> template class to fill in the default, boiler plate code for us. We give it the data type that we parse into, the last argument to the <code class="docutils literal notranslate"><span class="pre">parse</span></code> method, so that clients of our custom parser know what object type to pass in to the parse method. (Here we declare that we parse into ‘<code class="docutils literal notranslate"><span class="pre">unsigned</span></code>’ variables.)</p> <p>For most purposes, the only method that must be implemented in a custom parser is the <code class="docutils literal notranslate"><span class="pre">parse</span></code> method. The <code class="docutils literal notranslate"><span class="pre">parse</span></code> method is called whenever the option is invoked, passing in the option itself, the option name, the string to parse, and a reference to a return value. If the string to parse is not well-formed, the parser should output an error message and return true. Otherwise it should return false and set ‘<code class="docutils literal notranslate"><span class="pre">Val</span></code>’ to the parsed value. In our example, we implement <code class="docutils literal notranslate"><span class="pre">parse</span></code> as:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">bool</span> <span class="n">FileSizeParser</span><span class="o">::</span><span class="n">parse</span><span class="p">(</span><span class="n">cl</span><span class="o">::</span><span class="n">Option</span> <span class="o">&</span><span class="n">O</span><span class="p">,</span> <span class="n">StringRef</span> <span class="n">ArgName</span><span class="p">,</span> <span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="o">&</span><span class="n">Arg</span><span class="p">,</span> <span class="kt">unsigned</span> <span class="o">&</span><span class="n">Val</span><span class="p">)</span> <span class="p">{</span> <span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">ArgStart</span> <span class="o">=</span> <span class="n">Arg</span><span class="p">.</span><span class="n">c_str</span><span class="p">();</span> <span class="kt">char</span> <span class="o">*</span><span class="n">End</span><span class="p">;</span> <span class="c1">// Parse integer part, leaving 'End' pointing to the first non-integer char</span> <span class="n">Val</span> <span class="o">=</span> <span class="p">(</span><span class="kt">unsigned</span><span class="p">)</span><span class="n">strtol</span><span class="p">(</span><span class="n">ArgStart</span><span class="p">,</span> <span class="o">&</span><span class="n">End</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span> <span class="k">while</span> <span class="p">(</span><span class="mi">1</span><span class="p">)</span> <span class="p">{</span> <span class="k">switch</span> <span class="p">(</span><span class="o">*</span><span class="n">End</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span> <span class="k">case</span> <span class="mi">0</span><span class="o">:</span> <span class="k">return</span> <span class="nb">false</span><span class="p">;</span> <span class="c1">// No error</span> <span class="k">case</span> <span class="sc">'i'</span><span class="o">:</span> <span class="c1">// Ignore the 'i' in KiB if people use that</span> <span class="k">case</span> <span class="sc">'b'</span><span class="o">:</span> <span class="k">case</span> <span class="sc">'B'</span><span class="o">:</span> <span class="c1">// Ignore B suffix</span> <span class="k">break</span><span class="p">;</span> <span class="k">case</span> <span class="sc">'g'</span><span class="o">:</span> <span class="k">case</span> <span class="sc">'G'</span><span class="o">:</span> <span class="n">Val</span> <span class="o">*=</span> <span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p">;</span> <span class="k">break</span><span class="p">;</span> <span class="k">case</span> <span class="sc">'m'</span><span class="o">:</span> <span class="k">case</span> <span class="sc">'M'</span><span class="o">:</span> <span class="n">Val</span> <span class="o">*=</span> <span class="mi">1024</span><span class="o">*</span><span class="mi">1024</span><span class="p">;</span> <span class="k">break</span><span class="p">;</span> <span class="k">case</span> <span class="sc">'k'</span><span class="o">:</span> <span class="k">case</span> <span class="sc">'K'</span><span class="o">:</span> <span class="n">Val</span> <span class="o">*=</span> <span class="mi">1024</span><span class="p">;</span> <span class="k">break</span><span class="p">;</span> <span class="k">default</span><span class="o">:</span> <span class="c1">// Print an error message if unrecognized character!</span> <span class="k">return</span> <span class="n">O</span><span class="p">.</span><span class="n">error</span><span class="p">(</span><span class="s">"'"</span> <span class="o">+</span> <span class="n">Arg</span> <span class="o">+</span> <span class="s">"' value invalid for file size argument!"</span><span class="p">);</span> <span class="p">}</span> <span class="p">}</span> <span class="p">}</span> </pre></div> </div> <p>This function implements a very simple parser for the kinds of strings we are interested in. Although it has some holes (it allows “<code class="docutils literal notranslate"><span class="pre">123KKK</span></code>” for example), it is good enough for this example. Note that we use the option itself to print out the error message (the <code class="docutils literal notranslate"><span class="pre">error</span></code> method always returns true) in order to get a nice error message (shown below). Now that we have our parser class, we can use it like this:</p> <div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">static</span> <span class="n">cl</span><span class="o">::</span><span class="n">opt</span><span class="o"><</span><span class="kt">unsigned</span><span class="p">,</span> <span class="nb">false</span><span class="p">,</span> <span class="n">FileSizeParser</span><span class="o">></span> <span class="n">MFS</span><span class="p">(</span><span class="s">"max-file-size"</span><span class="p">,</span> <span class="n">cl</span><span class="o">::</span><span class="n">desc</span><span class="p">(</span><span class="s">"Maximum file size to accept"</span><span class="p">),</span> <span class="n">cl</span><span class="o">::</span><span class="n">value_desc</span><span class="p">(</span><span class="s">"size"</span><span class="p">));</span> </pre></div> </div> <p>Which adds this to the output of our program:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">OPTIONS</span><span class="p">:</span> <span class="o">-</span><span class="n">help</span> <span class="o">-</span> <span class="n">display</span> <span class="n">available</span> <span class="n">options</span> <span class="p">(</span><span class="o">-</span><span class="n">help</span><span class="o">-</span><span class="n">hidden</span> <span class="k">for</span> <span class="n">more</span><span class="p">)</span> <span class="o">...</span> <span class="o">-</span><span class="nb">max</span><span class="o">-</span><span class="n">file</span><span class="o">-</span><span class="n">size</span><span class="o">=<</span><span class="n">size</span><span class="o">></span> <span class="o">-</span> <span class="n">Maximum</span> <span class="n">file</span> <span class="n">size</span> <span class="n">to</span> <span class="n">accept</span> </pre></div> </div> <p>And we can test that our parse works correctly now (the test program just prints out the max-file-size argument value):</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ ./test MFS: 0 $ ./test -max-file-size=123MB MFS: 128974848 $ ./test -max-file-size=3G MFS: 3221225472 $ ./test -max-file-size=dog -max-file-size option: 'dog' value invalid for file size argument! </pre></div> </div> <p>It looks like it works. The error message that we get is nice and helpful, and we seem to accept reasonable file sizes. This wraps up the “custom parser” tutorial.</p> </div> <div class="section" id="exploiting-external-storage"> <h3><a class="toc-backref" href="#id46">Exploiting external storage</a><a class="headerlink" href="#exploiting-external-storage" title="Permalink to this headline">¶</a></h3> <p>Several of the LLVM libraries define static <code class="docutils literal notranslate"><span class="pre">cl::opt</span></code> instances that will automatically be included in any program that links with that library. This is a feature. However, sometimes it is necessary to know the value of the command line option outside of the library. In these cases the library does or should provide an external storage location that is accessible to users of the library. Examples of this include the <code class="docutils literal notranslate"><span class="pre">llvm::DebugFlag</span></code> exported by the <code class="docutils literal notranslate"><span class="pre">lib/Support/Debug.cpp</span></code> file and the <code class="docutils literal notranslate"><span class="pre">llvm::TimePassesIsEnabled</span></code> flag exported by the <code class="docutils literal notranslate"><span class="pre">lib/IR/PassManager.cpp</span></code> file.</p> </div> <div class="section" id="dynamically-adding-command-line-options"> <span id="dynamically-loaded-options"></span><h3><a class="toc-backref" href="#id47">Dynamically adding command line options</a><a class="headerlink" href="#dynamically-adding-command-line-options" title="Permalink to this headline">¶</a></h3> </div> </div> </div> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="CompilerWriterInfo.html" title="Architecture & Platform Information for Compiler Writers" >next</a> |</li> <li class="right" > <a href="CodingStandards.html" title="LLVM Coding Standards" >previous</a> |</li> <li><a href="http://llvm.org/">LLVM Home</a> | </li> <li><a href="index.html">Documentation</a>»</li> </ul> </div> <div class="footer" role="contentinfo"> © Copyright 2003-2020, LLVM Project. 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