<html>
<head>
<title>Debugging</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" href="theme/style.css" type="text/css">
</head>
<body>
<table width="100%" border="0" background="theme/bkd2.gif" cellspacing="2">
<tr>
<td width="10">
</td>
<td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Debugging</b></font>
</td>
<td width="112"><a href="http://spirit.sf.net"><img src="theme/spirit.gif" width="112" height="48" align="right" border="0"></a></td>
</tr>
</table>
<br>
<table border="0">
<tr>
<td width="10"></td>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="position_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="30"><a href="error_handling.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<p>The top-down nature of Spirit makes the generated parser easy to micro- debug
using the standard debugger bundled with the C++ compiler we are using. With
recursive-descent, the parse traversal utilizes the hardware stack through C++
function call mechanisms. There are no difficult to debug tables or state machines
that obscure the parsing logic flow. The stack trace we see in the debugger
follows faithfully the hierarchical grammar structure.</p>
<p> Since any production rule can initiate a parse traversal , it is a lot easier
to pinpoint the bugs by focusing on one or a few rules. For relatively complex
parsing tasks, the same way we write robust C++ programs, it is advisable to
develop a grammar iteratively on a per-module basis where each module is a small
subset of the complete grammar. That way, we can stress-test individual modules
piecemeal until we reach the top-most module. For instance, when developing
a scripting language, we can start with expressions, then move on to statements,
then functions, upwards until we have a complete grammar. </p>
<p> At some point when the grammar gets quite complicated, it is desirable to
visualize the parse traversal and see what's happening. There are some facilities
in the framework that aid in the visualisation of the parse traversal for the
purpose of debugging. The following macros enable these features.</p>
<a name="debugging_macros"></a>
<h2>Debugging Macros</h2>
<a name="spirit_assert_exception"></a>
<h3>BOOST_SPIRIT_ASSERT_EXCEPTION</h3>
<p> Spirit contains assertions that may activate when spirit is used incorrectly.
By default these assertions use the assert macro from the standard library.
If you want spirit to throw an exception instead, define <tt>BOOST_SPIRIT_ASSERT_EXCEPTION</tt>
to the name of the class that you want to be thrown. This class's constructor
will be passed a <tt>const char*</tt> stringified version of the file, line,
and assertion condition, when it is thrown. If you want to totally disable the
assertion, <tt>#define NDEBUG</tt>.</p>
<a name="spirit_debug"></a>
<h3>BOOST_SPIRIT_DEBUG</h3>
<p>Define this to enable debugging.</p>
<p>With debugging enabled, special output is generated at key points of the
parse process, using the standard output operator (<tt><span class="keyword">operator</span><span class="special"><<</span></tt>)
with <tt>BOOST_SPIRIT_DEBUG_OUT</tt> (default is <tt><span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span></tt>,
see below) as its left operand.</p>
<table width="80%" border="0" align="center">
<tr>
<td class="note_box"><img src="theme/note.gif"> In order to use spirit's
debugging support you must ensure that appropriate overloads of
<tt><span class="identifier">operator</span><span class="special"><<</span></tt>
taking <tt>BOOST_SPIRIT_DEBUG_OUT</tt> as its left operand are available.
The expected semantics are those of the standard output operator.<br>
<br>
These overloads may be provided either within the namespace where the
corresponding class is declared (will be found through Argument Dependent Lookup) or [within an
anonymous namespace] within <tt><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span></tt>,
so it is visible where it is called.<br>
<br>
<img src="theme/alert.gif"> Note in particular that when <tt>BOOST_SPIRIT_DEBUG_FLAGS_CLOSURES</tt>
is set, overloads of <tt><span class="identifier">operator</span><span class="special"><<</span></tt>
taking instances of the types used in closures as their right operands are required.<br>
<br>
You may find an example of overloading the output operator for
<tt><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span></tt>
in a <a href="faq.html#output_operator">related FAQ entry</a>.</td>
</tr>
</table>
<p>By default, if the <tt>BOOST_SPIRIT_DEBUG</tt> macro is defined, all available
debug output is generated. To fine tune the amount of generated text you can
define the <tt>BOOST_SPIRIT_DEBUG_FLAGS</tt> constant to be equal of a combination
of the following flags:</p>
<table width="90%" border="0" align="center">
<tr>
<td colspan="2" class="table_title"><b>Available flags to fine tune debug
output </b></td>
</tr>
<tr>
<td width="29%" height="27" class="table_cells"><tt>BOOST_SPIRIT_DEBUG_FLAGS_NODES</tt></td>
<td width="71%" class="table_cells"><p>print information about nodes (general
for all parsers)</p></td>
</tr>
<tr>
<td height="27" class="table_cells"><tt>BOOST_SPIRIT_DEBUG_FLAGS_TREES</tt></td>
<td class="table_cells"><p>print information about parse trees and AST's (general
for all tree parsers)</p></td>
</tr>
<tr>
<td height="27" class="table_cells"><tt>BOOST_SPIRIT_DEBUG_FLAGS_CLOSURES</tt></td>
<td class="table_cells">print information about closures (general for all
parsers with closures)</td>
</tr>
<tr>
<td height="27" class="table_cells"><tt>BOOST_SPIRIT_DEBUG_FLAGS_ESCAPE_CHAR</tt></td>
<td class="table_cells"><p>print information out of the <tt>esc_char_parser</tt></p></td>
</tr>
<tr>
<td height="27" class="table_cells"><tt>BOOST_SPIRIT_DEBUG_FLAGS_SLEX</tt></td>
<td class="table_cells">print information out of the <tt>SLEX</tt> parser</td>
</tr>
</table>
<p><a name="spirit_debug_out"></a> </p>
<h3>BOOST_SPIRIT_DEBUG_OUT</h3>
<p> Define this to redirect the debugging diagnostics printout to somewhere else
(e.g. a file or stream). Defaults to <tt>std::cout</tt>.</p>
<a name="spirit_debug_token printer"></a>
<h3>BOOST_SPIRIT_DEBUG_TOKEN_PRINTER</h3>
<p> The <tt>BOOST_SPIRIT_DEBUG_TOKEN_PRINTER</tt> macro allows you to redefine the way characters are printed on the stream. </p>
<p>If <tt>BOOST_SPIRIT_DEBUG_OUT</tt> is of type <tt>StreamT</tt>, the character type is <tt>CharT</tt> and <tt>BOOST_SPIRIT_DEBUG_TOKEN_PRINTER</tt> is
defined to <tt>foo</tt>, it must be compatible with this usage:</p>
<pre><code><span class=identifier> foo</span><span class=special>(</span><span class=identifier>StreamT</span><span class=special>, </span><span class=identifier>CharT</span><span class=special>)</span></code></pre>
<p>The default printer requires <tt>operator<<(StreamT, CharT)</tt> to
be defined. Additionaly, if <tt>CharT</tt> is convertible to a normal character
type (<tt>char</tt>, <tt>wchar_t</tt> or <tt>int</tt>), it prints control
characters in a friendly manner (e.g., when it receives <span class=special>'\n'</span> it
actually prints the <span class=special>\</span> and <span class=special>n</span> charactes,
instead of a newline).</p>
<a name="spirit_debug_print_some"></a>
<h3>BOOST_SPIRIT_DEBUG_PRINT_SOME</h3>
<p> The <tt>BOOST_SPIRIT_DEBUG_PRINT_SOME</tt> constant defines the number of
characters from the stream to be printed for diagnosis. This defaults to the
first 20 characters.</p>
<p><a name="spirit_debug_tracenode"></a> </p>
<h3>BOOST_SPIRIT_DEBUG_TRACENODE</h3>
<p> By default all parser nodes are traced. This constant may be used to redefine
this default. If this is <tt>1</tt> (<tt>true</tt>), then tracing is enabled
by default, if this constant is <tt>0</tt> (<tt>false</tt>), the tracing is
disabled by default. This preprocessor constant is set to <tt>1 </tt>(<tt>true</tt>)
by default.</p>
<p>Please note, that the following <tt>BOOST_SPIRIT_DEBUG_...() </tt>macros are
to be used at function scope only.</p>
<a name="spirit_debug_node_p_"></a>
<h3>BOOST_SPIRIT_DEBUG_NODE(p)</h3>
<p> Define this to print some debugging diagnostics for parser p. This macro</p>
<ul>
<li>Registers the parser name for debugging</li>
<li>Enables/disables the tracing for parser depending on <tt>BOOST_SPIRIT_DEBUG_TRACENODE</tt></li>
</ul>
<p> <b>Pre-parse</b>: Before entering the rule, the rule name followed by a peek
into the data at the current iterator position is printed.</p>
<p> <b>Post-parse</b>: After parsing the rule, the rule name followed by a peek
into the data at the current iterator position is printed. Here, <tt>'/'</tt>
before the rule name flags a succesful match while <tt>'#'</tt> before the rule
name flags an unsuccesful match.</p>
<p> The following are synonyms for <tt>BOOST_SPIRIT_DEBUG_NODE</tt></p>
<ol>
<li>BOOST_SPIRIT_DEBUG_RULE</li>
<li>BOOST_SPIRIT_DEBUG_GRAMMAR</li>
</ol>
<a name="spirit_trace_node_p__flag_"></a>
<h3>BOOST_SPIRIT_DEBUG_TRACE_NODE(p, flag)</h3>
<p> Similar to <tt>BOOST_SPIRIT_DEBUG_NODE</tt>. Additionally allows selective debugging.
This is useful in situations where we want to debug just a hand picked set of
nodes.</p>
<p> The following are synonyms for <tt>BOOST_SPIRIT_DEBUG_TRACE_NODE</tt></p>
<ol>
<li>BOOST_SPIRIT_DEBUG_TRACE_RULE</li>
<li>BOOST_SPIRIT_DEBUG_TRACE_GRAMMAR</li>
</ol>
<p><a name="spirit_trace_node_p__flag__name_"></a> </p>
<h3>BOOST_SPIRIT_DEBUG_TRACE_NODE_NAME(p, name, flag)</h3>
<p> Similar to <tt>BOOST_SPIRIT_DEBUG_NODE</tt>. Additionally allows selective
debugging and allows to specify the name used during debug printout. This is
useful in situations where we want to debug just a hand picked set of nodes.
The <tt>name</tt> may be redefined in situations, where the parser parameter does not reflect the name of the parser to debug.</p>
<p> The following are synonyms for <tt>BOOST_SPIRIT_DEBUG_TRACE_NODE</tt></p>
<ol>
<li>BOOST_SPIRIT_DEBUG_TRACE_RULE_NAME</li>
<li>BOOST_SPIRIT_DEBUG_TRACE_GRAMMAR_NAME</li>
</ol>
<hr>
<p>Here's the original calculator with debugging features enabled:</p>
<pre>
<code><span class=preprocessor>#define </span><span class=identifier>BOOST_SPIRIT_DEBUG </span><span class=comment>///$$$ DEFINE THIS BEFORE ANYTHING ELSE $$$///
</span><span class=preprocessor>#include </span><span class=string>"boost/spirit/include/classic.hpp"
</span><span class=comment>/***/
/*** CALCULATOR GRAMMAR DEFINITIONS HERE ***/
</span><span class=identifier>BOOST_SPIRIT_DEBUG_RULE</span><span class=special>(</span><span class=identifier>integer</span><span class=special>);
</span><span class=identifier>BOOST_SPIRIT_DEBUG_RULE</span><span class=special>(</span><span class=identifier>group</span><span class=special>);
</span><span class=identifier>BOOST_SPIRIT_DEBUG_RULE</span><span class=special>(</span><span class=identifier>factor</span><span class=special>);
</span><span class=identifier>BOOST_SPIRIT_DEBUG_RULE</span><span class=special>(</span><span class=identifier>term</span><span class=special>);
</span><span class=identifier>BOOST_SPIRIT_DEBUG_RULE</span><span class=special>(</span><span class=identifier>expr</span><span class=special>);
</span></code></pre>
<p> <img src="theme/note.gif" width="16" height="16"> Be sure to add the macros <strong>inside</strong> the grammar definition's constructor. Now here's a sample session with the calculator.</p>
<pre><code> <span class="preprocessor">Type an expression...or [q or Q] to quit</span>
<span class="preprocessor">1 + 2</span>
grammar(calc): "1 + 2"
rule(expression): "1 + 2"
rule(term): "1 + 2"
rule(factor): "1 + 2"
rule(integer): "1 + 2"
<span class="preprocessor">push 1</span>
/rule(integer): " + 2"
/rule(factor): " + 2"
/rule(term): " + 2"
rule(term): "2"
rule(factor): "2"
rule(integer): "2"
<span class="preprocessor">push 2</span>
/rule(integer): ""
/rule(factor): ""
/rule(term): ""
<span class="preprocessor">popped 1 and 2 from the stack. pushing 3 onto the stack.</span>
/rule(expression): ""
/grammar(calc): ""
<span class="preprocessor">-------------------------
Parsing succeeded
result = 3
-------------------------</span></code></pre>
<p> We typed in "1 + 2". Notice that there are two successful branches
from the top rule <tt>expr</tt>. The text in red is generated by the parser's
semantic actions while the others are generated by the debug-diagnostics of
our rules. Notice how the first <tt>integer</tt> rule took "1", the
first <tt>term</tt> rule took "+" and finally the second <tt>integer</tt>
rule took "2".</p>
<p>Please note the special meaning of the first characters appearing on the printed
lines:</p>
<ul>
<li>a single <span class="literal">'/'</span> starts a line containing the information
about a successfully matched parser node (<tt>rule<></tt>, <tt>grammar<></tt>
or <tt>subrule<></tt>)</li>
<li>a single <span class="literal">'#'</span> starts a line containing the information
about a failed parser node</li>
<li>a single <span class="literal">'^'</span> starts a line containing the first member (return value/synthesised
attribute) of the closure of a successfully matched parser node.</li>
</ul>
<p>Check out <a href="../example/fundamental/calc_debug.cpp">calc_debug.cpp</a> to see debugging in action. </p>
<table border="0">
<tr>
<td width="10"></td>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="position_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="30"><a href="error_handling.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<br>
<hr size="1">
<p class="copyright">Copyright © 1998-2003 Joel de Guzman<br>
Copyright © 2003 Hartmut Kaiser<br>
<br>
<font size="2">Use, modification and distribution is subject to the Boost Software
License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt)</font></p>
<p class="copyright"> </p>
</body>
</html>
