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| <div class="subsection-level-extent" id="g_t_0023line-Syntax-Details"> |
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| <p> |
| Previous: <a href="_0023line-and-TeX.html" accesskey="p" rel="prev">‘<samp class="samp">#line</samp>’ and TeX</a>, Up: <a href="External-Macro-Processors.html" accesskey="u" rel="up">External Macro Processors: Line Directives</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p> |
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| <h4 class="subsection" id="g_t_0023line-Syntax-Details-1">16.6.3 ‘<samp class="samp">#line</samp>’ Syntax Details</h4> |
| |
| <a class="index-entry-id" id="index-_0023line-directive-2"></a> |
| <a class="index-entry-id" id="index-Syntax-details_002c-_0023line"></a> |
| <a class="index-entry-id" id="index-Regular-expression_002c-for-_0023line"></a> |
| |
| <p>Syntax details for the ‘<samp class="samp">#line</samp>’ directive: the ‘<samp class="samp">#</samp>’ character |
| can be preceded or followed by whitespace, the word ‘<samp class="samp">line</samp>’ is |
| optional, and the file name can be followed by a whitespace-separated |
| list of integers (these are so-called “flags” output by CPP in some |
| cases). For those who like to know the gory details, the actual |
| (Perl) regular expression which is matched is this: |
| </p> |
| <div class="example"> |
| <pre class="example-preformatted">/^\s*#\s*(line)? (\d+)(( "([^"]+)")(\s+\d+)*)?\s*$/ |
| </pre></div> |
| |
| <p>As far as we’ve been able to tell, the trailing integer flags only |
| occur in conjunction with a file name, so that is reflected in the |
| regular expression. |
| </p> |
| <p>As an example, the following is a syntactically valid ‘<samp class="samp">#line</samp>’ |
| directive, meaning line 1 of <samp class="file">/usr/include/stdio.h</samp>: |
| </p> |
| <div class="example"> |
| <pre class="example-preformatted"># 1 "/usr/include/stdio.h" 2 3 4 |
| </pre></div> |
| |
| <p>Unfortunately, the quoted file name (‘<samp class="samp">"..."</samp>’) has to be optional, |
| because M4 (especially) can often generate ‘<samp class="samp">#line</samp>’ directives |
| within a single file. Since the ‘<samp class="samp">line</samp>’ is also optional, the |
| result is that lines might match which you wouldn’t expect, e.g., |
| </p> |
| <div class="example"> |
| <pre class="example-preformatted"># 1 |
| </pre></div> |
| |
| <p>The possible solutions are described above (see <a class="pxref" href="_0023line-Directive.html">‘<samp class="samp">#line</samp>’ Directive</a>). |
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