| <html lang="en"> |
| <head> |
| <title>Preprocessor Output - The C Preprocessor</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The C Preprocessor"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="prev" href="Other-Directives.html#Other-Directives" title="Other Directives"> |
| <link rel="next" href="Traditional-Mode.html#Traditional-Mode" title="Traditional Mode"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| Copyright (C) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, |
| 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, |
| 2008, 2009, 2010 |
| Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.2 or |
| any later version published by the Free Software Foundation. A copy of |
| the license is included in the |
| section entitled ``GNU Free Documentation License''. |
| |
| This manual contains no Invariant Sections. The Front-Cover Texts are |
| (a) (see below), and the Back-Cover Texts are (b) (see below). |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development. |
| --> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Preprocessor-Output"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Traditional-Mode.html#Traditional-Mode">Traditional Mode</a>, |
| Previous: <a rel="previous" accesskey="p" href="Other-Directives.html#Other-Directives">Other Directives</a>, |
| Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a> |
| <hr> |
| </div> |
| |
| <h2 class="chapter">9 Preprocessor Output</h2> |
| |
| <p>When the C preprocessor is used with the C, C++, or Objective-C |
| compilers, it is integrated into the compiler and communicates a stream |
| of binary tokens directly to the compiler's parser. However, it can |
| also be used in the more conventional standalone mode, where it produces |
| textual output. |
| <!-- FIXME: Document the library interface. --> |
| |
| <p><a name="index-output-format-107"></a>The output from the C preprocessor looks much like the input, except |
| that all preprocessing directive lines have been replaced with blank |
| lines and all comments with spaces. Long runs of blank lines are |
| discarded. |
| |
| <p>The ISO standard specifies that it is implementation defined whether a |
| preprocessor preserves whitespace between tokens, or replaces it with |
| e.g. a single space. In GNU CPP, whitespace between tokens is collapsed |
| to become a single space, with the exception that the first token on a |
| non-directive line is preceded with sufficient spaces that it appears in |
| the same column in the preprocessed output that it appeared in the |
| original source file. This is so the output is easy to read. |
| See <a href="Differences-from-previous-versions.html#Differences-from-previous-versions">Differences from previous versions</a>. CPP does not insert any |
| whitespace where there was none in the original source, except where |
| necessary to prevent an accidental token paste. |
| |
| <p><a name="index-linemarkers-108"></a>Source file name and line number information is conveyed by lines |
| of the form |
| |
| <pre class="smallexample"> # <var>linenum</var> <var>filename</var> <var>flags</var> |
| </pre> |
| <p class="noindent">These are called <dfn>linemarkers</dfn>. They are inserted as needed into |
| the output (but never within a string or character constant). They mean |
| that the following line originated in file <var>filename</var> at line |
| <var>linenum</var>. <var>filename</var> will never contain any non-printing |
| characters; they are replaced with octal escape sequences. |
| |
| <p>After the file name comes zero or more flags, which are ‘<samp><span class="samp">1</span></samp>’, |
| ‘<samp><span class="samp">2</span></samp>’, ‘<samp><span class="samp">3</span></samp>’, or ‘<samp><span class="samp">4</span></samp>’. If there are multiple flags, spaces |
| separate them. Here is what the flags mean: |
| |
| <dl> |
| <dt>‘<samp><span class="samp">1</span></samp>’<dd>This indicates the start of a new file. |
| <br><dt>‘<samp><span class="samp">2</span></samp>’<dd>This indicates returning to a file (after having included another file). |
| <br><dt>‘<samp><span class="samp">3</span></samp>’<dd>This indicates that the following text comes from a system header file, |
| so certain warnings should be suppressed. |
| <br><dt>‘<samp><span class="samp">4</span></samp>’<dd>This indicates that the following text should be treated as being |
| wrapped in an implicit <code>extern "C"</code> block. |
| <!-- maybe cross reference NO_IMPLICIT_EXTERN_C --> |
| </dl> |
| |
| <p>As an extension, the preprocessor accepts linemarkers in non-assembler |
| input files. They are treated like the corresponding ‘<samp><span class="samp">#line</span></samp>’ |
| directive, (see <a href="Line-Control.html#Line-Control">Line Control</a>), except that trailing flags are |
| permitted, and are interpreted with the meanings described above. If |
| multiple flags are given, they must be in ascending order. |
| |
| <p>Some directives may be duplicated in the output of the preprocessor. |
| These are ‘<samp><span class="samp">#ident</span></samp>’ (always), ‘<samp><span class="samp">#pragma</span></samp>’ (only if the |
| preprocessor does not handle the pragma itself), and ‘<samp><span class="samp">#define</span></samp>’ and |
| ‘<samp><span class="samp">#undef</span></samp>’ (with certain debugging options). If this happens, the |
| ‘<samp><span class="samp">#</span></samp>’ of the directive will always be in the first column, and there |
| will be no space between the ‘<samp><span class="samp">#</span></samp>’ and the directive name. If macro |
| expansion happens to generate tokens which might be mistaken for a |
| duplicated directive, a space will be inserted between the ‘<samp><span class="samp">#</span></samp>’ and |
| the directive name. |
| |
| </body></html> |
| |
