<html> <head> <title>Position Iterator</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>Position Iterator</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="file_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td> <td width="20"><a href="debugging.html"><img src="theme/r_arr.gif" border="0"></a></td> </tr> </table> <p>Often, when writing a parser that is able to detect errors in the format of the input stream, we want it to communicate to the user where the error happened within that input. The most classic is when writing a compiler or interpreter that detects syntactical errors in the parsed program, indicating the line number and maybe even the position within the line where the error was found.</p> <p> The class position_iterator is a tool provided within Spirit that allows parser writers to easily implement this functionality. The concept is quite simple: this class is an iterator wrapper that keeps track of the current position within the file, including current file, line and column. It requires a single template parameter, which should be the type of the iterator that is to be wrapped.</p> <p> In order to use it, you'll need to add the following include:</p> <pre> <code><span class=preprocessor>#include </span><span class=special><</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>spirit</span><span class=special>/</span><span class=identifier>iterator</span><span class=special>/</span><span class=identifier>position_iterator</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>></span></code></pre> <p> Or include all the iterators in Spirit:</p> <pre> <code><span class=preprocessor>#include </span><span class=special><</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>spirit</span><span class=special>/</span><span class=identifier>iterator</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>></span></code></pre> <p> To construct the wrapper, it needs both the begin and end iterators of the input sequence, and the file name of the input sequence. Optionally, you can also specify the starting line and column numbers, which default to 1. Default construction, with no parameters, creates a generic end-of-sequence iterator, in a similar manner as it's done in the stream operators of the standard C++ library.</p> <p> The wrapped iterator must belong to the input or forward iterator category, and the position_iterator just inherits that category.</p> <p> For example, to create begin and end positional iterators from an input C- string, you'd use:</p> <pre> <code><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>inputstring </span><span class=special>= </span><span class=string>"..."</span><span class=special>; </span><span class=keyword>typedef </span><span class=identifier>position_iterator</span><span class=special><</span><span class=keyword>char </span><span class=keyword>const</span><span class=special>*> </span><span class=identifier>iterator_t</span><span class=special>; </span><span class=identifier>iterator_t </span><span class=identifier>begin</span><span class=special>(</span><span class=identifier>inputstring</span><span class=special>, </span><span class=identifier>inputstring</span><span class=special>+</span><span class=identifier>strlen</span><span class=special>(</span><span class=identifier>inputstring</span><span class=special>)); </span><span class=identifier>iterator_t </span><span class=identifier>end</span><span class=special>;</span></code></pre> <a name="operations"></a> <h2>Operations</h2> <pre> <code><span class=keyword>void </span><span class=identifier>set_position</span><span class=special>(</span><span class=identifier>file_position </span><span class=keyword>const</span><span class=special>&);</span></code></pre> <p> Call this function when you need to change the current position stored in the iterator. For example, if parsing C-style #include directives, the included file's input must be marked by restarting the file and column to 1 and 1 and the name to the new file's name.<br> </p> <pre> <code><span class=identifier>file_position </span><span class=keyword>const</span><span class=special>& </span><span class=identifier>get_position</span><span class=special>() </span><span class=keyword>const</span><span class=special>;</span></code></pre> <p> Call this function to retrieve the current position.</p> <pre> <code><span class=keyword>void </span><span class=identifier>set_tabchars</span><span class=special>(</span><span class=keyword>int</span><span class=special>);</span></code></pre> <p> Call this to set the number of tabs per character. This value is necessary to correctly track the column number.<br> </p> <p> <a name="file_position"></a> </p> <h2>file_position</h2> <p> file_position is a structure that holds the position within a file. Its fields are:</p> <table width="90%" border="0" align="center"> <tr> <td class="table_title" colspan="2">file_position fields</td> </tr> <tr> <td class="table_cells" width="26%"><code><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>file</span><span class=special>;</span></code></td> <td class="table_cells" width="74%">Name of the file. Hopefully a full pathname</td> </tr> <tr> <td class="table_cells" width="26%"><code><span class=keyword>int</span><span class=identifier> line</span><span class=special>;</span></code></td> <td class="table_cells" width="74%">Line number within the file. By default, the first line is number 1</td> </tr> <tr> <td class="table_cells" width="26%"><code><span class=keyword>int </span><span class=identifier>column</span><span class=special>;</span></code></td> <td class="table_cells" width="74%">Column position within the file. The first column is 1</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="file_iterator.html"><img src="theme/l_arr.gif" border="0"></a></td> <td width="20"><a href="debugging.html"><img src="theme/r_arr.gif" border="0"></a></td> </tr> </table> <hr size="1"> <p class="copyright">Copyright © 2002 Juan Carlos Arevalo-Baeza<br> <br> <font size="2">Permission to copy, use, modify, sell and distribute this document is granted provided this copyright notice appears in all copies. This document is provided "as is" without express or implied warranty, and with no claim as to its suitability for any purpose. </font> </p> <p class="copyright"> </p> <p> </p> </body> </html>