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 <a name="Standard-Predefined-Macros"></a>
 <div class="header">
 <p>
 Next: <a href="Common-Predefined-Macros.html#Common-Predefined-Macros" accesskey="n" rel="next">Common Predefined Macros</a>, Up: <a href="Predefined-Macros.html#Predefined-Macros" accesskey="u" rel="up">Predefined Macros</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Standard-Predefined-Macros-1"></a>
 <h4 class="subsection">3.7.1 Standard Predefined Macros</h4>
 <a name="index-standard-predefined-macros_002e"></a>

 <p>The standard predefined macros are specified by the relevant
 language standards, so they are available with all compilers that
 implement those standards.  Older compilers may not provide all of
 them.  Their names all start with double underscores.
 </p>
 <dl compact="compact">
 <dt><code>__FILE__</code></dt>
 <dd><p>This macro expands to the name of the current input file, in the form of
 a C string constant.  This is the path by which the preprocessor opened
 the file, not the short name specified in &lsquo;<samp>#include</samp>&rsquo; or as the
 input file name argument.  For example,
 <code>&quot;/usr/local/include/myheader.h&quot;</code> is a possible expansion of this
 macro.
 </p>
 </dd>
 <dt><code>__LINE__</code></dt>
 <dd><p>This macro expands to the current input line number, in the form of a
 decimal integer constant.  While we call it a predefined macro, it&rsquo;s
 a pretty strange macro, since its &ldquo;definition&rdquo; changes with each
 new line of source code.
 </p></dd>
 </dl>

 <p><code>__FILE__</code> and <code>__LINE__</code> are useful in generating an error
 message to report an inconsistency detected by the program; the message
 can state the source line at which the inconsistency was detected.  For
 example,
 </p>
 <div class="smallexample">
 <pre class="smallexample">fprintf (stderr, &quot;Internal error: &quot;
                  &quot;negative string length &quot;
                  &quot;%d at %s, line %d.&quot;,
          length, __FILE__, __LINE__);
 </pre></div>

 <p>An &lsquo;<samp>#include</samp>&rsquo; directive changes the expansions of <code>__FILE__</code>
 and <code>__LINE__</code> to correspond to the included file.  At the end of
 that file, when processing resumes on the input file that contained
 the &lsquo;<samp>#include</samp>&rsquo; directive, the expansions of <code>__FILE__</code> and
 <code>__LINE__</code> revert to the values they had before the
 &lsquo;<samp>#include</samp>&rsquo; (but <code>__LINE__</code> is then incremented by one as
 processing moves to the line after the &lsquo;<samp>#include</samp>&rsquo;).
 </p>
 <p>A &lsquo;<samp>#line</samp>&rsquo; directive changes <code>__LINE__</code>, and may change
 <code>__FILE__</code> as well.  See <a href="Line-Control.html#Line-Control">Line Control</a>.
 </p>
 <p>C99 introduces <code>__func__</code>, and GCC has provided <code>__FUNCTION__</code>
 for a long time.  Both of these are strings containing the name of the
 current function (there are slight semantic differences; see the GCC
 manual).  Neither of them is a macro; the preprocessor does not know the
 name of the current function.  They tend to be useful in conjunction
 with <code>__FILE__</code> and <code>__LINE__</code>, though.
 </p>
 <dl compact="compact">
 <dt><code>__DATE__</code></dt>
 <dd><p>This macro expands to a string constant that describes the date on which
 the preprocessor is being run.  The string constant contains eleven
 characters and looks like <code>&quot;Feb&nbsp;12&nbsp;1996&quot;<!-- /@w --></code>.  If the day of the
 month is less than 10, it is padded with a space on the left.
 </p>
 <p>If GCC cannot determine the current date, it will emit a warning message
 (once per compilation) and <code>__DATE__</code> will expand to
 <code>&quot;???&nbsp;??&nbsp;????&quot;<!-- /@w --></code>.
 </p>
 </dd>
 <dt><code>__TIME__</code></dt>
 <dd><p>This macro expands to a string constant that describes the time at
 which the preprocessor is being run.  The string constant contains
 eight characters and looks like <code>&quot;23:59:01&quot;</code>.
 </p>
 <p>If GCC cannot determine the current time, it will emit a warning message
 (once per compilation) and <code>__TIME__</code> will expand to
 <code>&quot;??:??:??&quot;</code>.
 </p>
 </dd>
 <dt><code>__STDC__</code></dt>
 <dd><p>In normal operation, this macro expands to the constant 1, to signify
 that this compiler conforms to ISO Standard C.  If GNU CPP is used with
 a compiler other than GCC, this is not necessarily true; however, the
 preprocessor always conforms to the standard unless the
 <samp>-traditional-cpp</samp> option is used.
 </p>
 <p>This macro is not defined if the <samp>-traditional-cpp</samp> option is used.
 </p>
 <p>On some hosts, the system compiler uses a different convention, where
 <code>__STDC__</code> is normally 0, but is 1 if the user specifies strict
 conformance to the C Standard.  CPP follows the host convention when
 processing system header files, but when processing user files
 <code>__STDC__</code> is always 1.  This has been reported to cause problems;
 for instance, some versions of Solaris provide X Windows headers that
 expect <code>__STDC__</code> to be either undefined or 1.  See <a href="Invocation.html#Invocation">Invocation</a>.
 </p>
 </dd>
 <dt><code>__STDC_VERSION__</code></dt>
 <dd><p>This macro expands to the C Standard&rsquo;s version number, a long integer
 constant of the form <code><var>yyyy</var><var>mm</var>L</code> where <var>yyyy</var> and
 <var>mm</var> are the year and month of the Standard version.  This signifies
 which version of the C Standard the compiler conforms to.  Like
 <code>__STDC__</code>, this is not necessarily accurate for the entire
 implementation, unless GNU CPP is being used with GCC.
 </p>
 <p>The value <code>199409L</code> signifies the 1989 C standard as amended in
 1994, which is the current default; the value <code>199901L</code> signifies
 the 1999 revision of the C standard.  Support for the 1999 revision is
 not yet complete.
 </p>
 <p>This macro is not defined if the <samp>-traditional-cpp</samp> option is
 used, nor when compiling C++ or Objective-C.
 </p>
 </dd>
 <dt><code>__STDC_HOSTED__</code></dt>
 <dd><p>This macro is defined, with value 1, if the compiler&rsquo;s target is a
 <em>hosted environment</em>.  A hosted environment has the complete
 facilities of the standard C library available.
 </p>
 </dd>
 <dt><code>__cplusplus</code></dt>
 <dd><p>This macro is defined when the C++ compiler is in use.  You can use
 <code>__cplusplus</code> to test whether a header is compiled by a C compiler
 or a C++ compiler.  This macro is similar to <code>__STDC_VERSION__</code>, in
 that it expands to a version number.  Depending on the language standard
 selected, the value of the macro is <code>199711L</code>, as mandated by the
 1998 C++ standard; <code>201103L</code>, per the 2011 C++ standard; an
 unspecified value strictly larger than <code>201103L</code> for the experimental
 languages enabled by <samp>-std=c++1y</samp> and <samp>-std=gnu++1y</samp>.
 </p>
 </dd>
 <dt><code>__OBJC__</code></dt>
 <dd><p>This macro is defined, with value 1, when the Objective-C compiler is in
 use.  You can use <code>__OBJC__</code> to test whether a header is compiled
 by a C compiler or an Objective-C compiler.
 </p>
 </dd>
 <dt><code>__ASSEMBLER__</code></dt>
 <dd><p>This macro is defined with value 1 when preprocessing assembly
 language.
 </p>
 </dd>
 </dl>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Common-Predefined-Macros.html#Common-Predefined-Macros" accesskey="n" rel="next">Common Predefined Macros</a>, Up: <a href="Predefined-Macros.html#Predefined-Macros" accesskey="u" rel="up">Predefined Macros</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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	<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
	<a name="Standard-Predefined-Macros"></a>
	<div class="header">
	<p>
	Next: <a href="Common-Predefined-Macros.html#Common-Predefined-Macros" accesskey="n" rel="next">Common Predefined Macros</a>, Up: <a href="Predefined-Macros.html#Predefined-Macros" accesskey="u" rel="up">Predefined Macros</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Standard-Predefined-Macros-1"></a>
	<h4 class="subsection">3.7.1 Standard Predefined Macros</h4>
	<a name="index-standard-predefined-macros_002e"></a>

	<p>The standard predefined macros are specified by the relevant
	language standards, so they are available with all compilers that
	implement those standards. Older compilers may not provide all of
	them. Their names all start with double underscores.
	</p>
	<dl compact="compact">
	<dt><code>__FILE__</code></dt>
	<dd><p>This macro expands to the name of the current input file, in the form of
	a C string constant. This is the path by which the preprocessor opened
	the file, not the short name specified in ‘<samp>#include</samp>’ or as the
	input file name argument. For example,
	<code>"/usr/local/include/myheader.h"</code> is a possible expansion of this
	macro.
	</p>
	</dd>
	<dt><code>__LINE__</code></dt>
	<dd><p>This macro expands to the current input line number, in the form of a
	decimal integer constant. While we call it a predefined macro, it’s
	a pretty strange macro, since its “definition” changes with each
	new line of source code.
	</p></dd>
	</dl>

	<p><code>__FILE__</code> and <code>__LINE__</code> are useful in generating an error
	message to report an inconsistency detected by the program; the message
	can state the source line at which the inconsistency was detected. For
	example,
	</p>
	<div class="smallexample">
	<pre class="smallexample">fprintf (stderr, "Internal error: "
	"negative string length "
	"%d at %s, line %d.",
	length, __FILE__, __LINE__);
	</pre></div>

	<p>An ‘<samp>#include</samp>’ directive changes the expansions of <code>__FILE__</code>
	and <code>__LINE__</code> to correspond to the included file. At the end of
	that file, when processing resumes on the input file that contained
	the ‘<samp>#include</samp>’ directive, the expansions of <code>__FILE__</code> and
	<code>__LINE__</code> revert to the values they had before the
	‘<samp>#include</samp>’ (but <code>__LINE__</code> is then incremented by one as
	processing moves to the line after the ‘<samp>#include</samp>’).
	</p>
	<p>A ‘<samp>#line</samp>’ directive changes <code>__LINE__</code>, and may change
	<code>__FILE__</code> as well. See <a href="Line-Control.html#Line-Control">Line Control</a>.
	</p>
	<p>C99 introduces <code>__func__</code>, and GCC has provided <code>__FUNCTION__</code>
	for a long time. Both of these are strings containing the name of the
	current function (there are slight semantic differences; see the GCC
	manual). Neither of them is a macro; the preprocessor does not know the
	name of the current function. They tend to be useful in conjunction
	with <code>__FILE__</code> and <code>__LINE__</code>, though.
	</p>
	<dl compact="compact">
	<dt><code>__DATE__</code></dt>
	<dd><p>This macro expands to a string constant that describes the date on which
	the preprocessor is being run. The string constant contains eleven
	characters and looks like <code>"Feb 12 1996"<!-- /@w --></code>. If the day of the
	month is less than 10, it is padded with a space on the left.
	</p>
	<p>If GCC cannot determine the current date, it will emit a warning message
	(once per compilation) and <code>__DATE__</code> will expand to
	<code>"??? ?? ????"<!-- /@w --></code>.
	</p>
	</dd>
	<dt><code>__TIME__</code></dt>
	<dd><p>This macro expands to a string constant that describes the time at
	which the preprocessor is being run. The string constant contains
	eight characters and looks like <code>"23:59:01"</code>.
	</p>
	<p>If GCC cannot determine the current time, it will emit a warning message
	(once per compilation) and <code>__TIME__</code> will expand to
	<code>"??:??:??"</code>.
	</p>
	</dd>
	<dt><code>__STDC__</code></dt>
	<dd><p>In normal operation, this macro expands to the constant 1, to signify
	that this compiler conforms to ISO Standard C. If GNU CPP is used with
	a compiler other than GCC, this is not necessarily true; however, the
	preprocessor always conforms to the standard unless the
	<samp>-traditional-cpp</samp> option is used.
	</p>
	<p>This macro is not defined if the <samp>-traditional-cpp</samp> option is used.
	</p>
	<p>On some hosts, the system compiler uses a different convention, where
	<code>__STDC__</code> is normally 0, but is 1 if the user specifies strict
	conformance to the C Standard. CPP follows the host convention when
	processing system header files, but when processing user files
	<code>__STDC__</code> is always 1. This has been reported to cause problems;
	for instance, some versions of Solaris provide X Windows headers that
	expect <code>__STDC__</code> to be either undefined or 1. See <a href="Invocation.html#Invocation">Invocation</a>.
	</p>
	</dd>
	<dt><code>__STDC_VERSION__</code></dt>
	<dd><p>This macro expands to the C Standard’s version number, a long integer
	constant of the form <code><var>yyyy</var><var>mm</var>L</code> where <var>yyyy</var> and
	<var>mm</var> are the year and month of the Standard version. This signifies
	which version of the C Standard the compiler conforms to. Like
	<code>__STDC__</code>, this is not necessarily accurate for the entire
	implementation, unless GNU CPP is being used with GCC.
	</p>
	<p>The value <code>199409L</code> signifies the 1989 C standard as amended in
	1994, which is the current default; the value <code>199901L</code> signifies
	the 1999 revision of the C standard. Support for the 1999 revision is
	not yet complete.
	</p>
	<p>This macro is not defined if the <samp>-traditional-cpp</samp> option is
	used, nor when compiling C++ or Objective-C.
	</p>
	</dd>
	<dt><code>__STDC_HOSTED__</code></dt>
	<dd><p>This macro is defined, with value 1, if the compiler’s target is a
	<em>hosted environment</em>. A hosted environment has the complete
	facilities of the standard C library available.
	</p>
	</dd>
	<dt><code>__cplusplus</code></dt>
	<dd><p>This macro is defined when the C++ compiler is in use. You can use
	<code>__cplusplus</code> to test whether a header is compiled by a C compiler
	or a C++ compiler. This macro is similar to <code>__STDC_VERSION__</code>, in
	that it expands to a version number. Depending on the language standard
	selected, the value of the macro is <code>199711L</code>, as mandated by the
	1998 C++ standard; <code>201103L</code>, per the 2011 C++ standard; an
	unspecified value strictly larger than <code>201103L</code> for the experimental
	languages enabled by <samp>-std=c++1y</samp> and <samp>-std=gnu++1y</samp>.
	</p>
	</dd>
	<dt><code>__OBJC__</code></dt>
	<dd><p>This macro is defined, with value 1, when the Objective-C compiler is in
	use. You can use <code>__OBJC__</code> to test whether a header is compiled
	by a C compiler or an Objective-C compiler.
	</p>
	</dd>
	<dt><code>__ASSEMBLER__</code></dt>
	<dd><p>This macro is defined with value 1 when preprocessing assembly
	language.
	</p>
	</dd>
	</dl>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Common-Predefined-Macros.html#Common-Predefined-Macros" accesskey="n" rel="next">Common Predefined Macros</a>, Up: <a href="Predefined-Macros.html#Predefined-Macros" accesskey="u" rel="up">Predefined Macros</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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