This has been fixed for libstdc++ releases greater than 3.0.3.
</p></td></tr><tr class="question"><td align="left" valign="top"><a id="faq.predefined"></a><a id="q-predefined"></a><p><strong>4.3.</strong></p></td><td align="left" valign="top"><p>
<code class="constant">_XOPEN_SOURCE</code> and <code class="constant">_GNU_SOURCE</code> are always defined?
- </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-predefined"></a></td><td align="left" valign="top"><p>On Solaris, <span class="command"><strong>g++</strong></span> (but not <span class="command"><strong>gcc</strong></span>)
+ </p></td></tr><tr class="answer"><td align="left" valign="top"><a id="a-predefined"></a></td><td align="left" valign="top"><p>On GNU/Linux, <span class="command"><strong>g++</strong></span> (but not <span class="command"><strong>gcc</strong></span>)
always defines the preprocessor macro
- <code class="constant">_XOPEN_SOURCE</code>. On GNU/Linux, the same happens
- with <code class="constant">_GNU_SOURCE</code>. (This is not an exhaustive list;
+ <code class="constant">_GNU_SOURCE</code>. On Solaris, the same happens
+ with <code class="constant">_XOPEN_SOURCE</code>. (This is not an exhaustive list;
other macros and other platforms are also affected.)
</p><p>These macros are typically used in C library headers, guarding new
- versions of functions from their older versions. The C++98 standard
- library includes the C standard library, but it requires the C90
- version, which for backwards-compatibility reasons is often not the
- default for many vendors.
- </p><p>More to the point, the C++ standard requires behavior which is only
- available on certain platforms after certain symbols are defined.
+ versions of functions from their older versions. Historically,
+ libstdc++ needed these macros to ensure that the headers provided by
+ the C library declared all the functions that libstdc++ relies on.
+ For example, functions for working with <code class="code">long long</code>,
+ such as <code class="function">strtoll</code>, are needed by libstdc++ but
+ were not part of the C90 standard.
+ </p><p>Additionally the C++ standard requires behavior which is only
+ available on certain platforms after certain macros are defined.
Usually the issue involves I/O-related typedefs. In order to
- ensure correctness, the compiler simply predefines those symbols.
- </p><p>Note that it's not enough to <code class="literal">#define</code> them only when the library is
- being built (during installation). Since we don't have an 'export'
- keyword, much of the library exists as headers, which means that
- the symbols must also be defined as your programs are parsed and
+ ensure correctness, the compiler simply predefines those macros.
+ </p><p>Note that it's not enough to <code class="literal">#define</code> them
+ only when the library is being built (during installation).
+ Much of the library exists as headers, which means that
+ the macros must also be defined as your programs are parsed and
compiled.
- </p><p>To see which symbols are defined, look for
+ </p><p>To see which macros are defined, look for
<code class="varname">CPLUSPLUS_CPP_SPEC</code> in
the gcc config headers for your target (and try changing them to
see what happens when building complicated code). You can also run
</p><p>The first file to create in this directory, should be called
<code class="code">os_defines.h</code>. This file contains basic macro definitions
that are required to allow the C++ library to work with your C library.
- </p><p>Several libstdc++ source files unconditionally define the macro
-<code class="code">_POSIX_SOURCE</code>. On many systems, defining this macro causes
-large portions of the C library header files to be eliminated
-at preprocessing time. Therefore, you may have to <code class="code">#undef</code> this
-macro, or define other macros (like <code class="code">_LARGEFILE_SOURCE</code> or
-<code class="code">__EXTENSIONS__</code>). You won't know what macros to define or
-undefine at this point; you'll have to try compiling the library and
-seeing what goes wrong. If you see errors about calling functions
-that have not been declared, look in your C library headers to see if
-the functions are declared there, and then figure out what macros you
-need to define. You will need to add them to the
-<code class="code">CPLUSPLUS_CPP_SPEC</code> macro in the GCC configuration file for your
-target. It will not work to simply define these macros in
-<code class="code">os_defines.h</code>.
</p><p>At this time, there are a few libstdc++-specific macros which may be
defined:
</p><p><code class="code">_GLIBCXX_USE_C99_CHECK</code> may be defined to 1 to check C99
<constant>_XOPEN_SOURCE</constant> and <constant>_GNU_SOURCE</constant> are always defined?
</para>
</question>
+
<answer xml:id="a-predefined">
- <para>On Solaris, <command>g++</command> (but not <command>gcc</command>)
+ <para>On GNU/Linux, <command>g++</command> (but not <command>gcc</command>)
always defines the preprocessor macro
- <constant>_XOPEN_SOURCE</constant>. On GNU/Linux, the same happens
- with <constant>_GNU_SOURCE</constant>. (This is not an exhaustive list;
+ <constant>_GNU_SOURCE</constant>. On Solaris, the same happens
+ with <constant>_XOPEN_SOURCE</constant>. (This is not an exhaustive list;
other macros and other platforms are also affected.)
</para>
<para>These macros are typically used in C library headers, guarding new
- versions of functions from their older versions. The C++98 standard
- library includes the C standard library, but it requires the C90
- version, which for backwards-compatibility reasons is often not the
- default for many vendors.
+ versions of functions from their older versions. Historically,
+ libstdc++ needed these macros to ensure that the headers provided by
+ the C library declared all the functions that libstdc++ relies on.
+ For example, functions for working with <code>long long</code>,
+ such as <function>strtoll</function>, are needed by libstdc++ but
+ were not part of the C90 standard.
</para>
- <para>More to the point, the C++ standard requires behavior which is only
- available on certain platforms after certain symbols are defined.
+ <para>Additionally the C++ standard requires behavior which is only
+ available on certain platforms after certain macros are defined.
Usually the issue involves I/O-related typedefs. In order to
- ensure correctness, the compiler simply predefines those symbols.
+ ensure correctness, the compiler simply predefines those macros.
</para>
- <para>Note that it's not enough to <literal>#define</literal> them only when the library is
- being built (during installation). Since we don't have an 'export'
- keyword, much of the library exists as headers, which means that
- the symbols must also be defined as your programs are parsed and
+ <para>Note that it's not enough to <literal>#define</literal> them
+ only when the library is being built (during installation).
+ Much of the library exists as headers, which means that
+ the macros must also be defined as your programs are parsed and
compiled.
</para>
- <para>To see which symbols are defined, look for
+ <para>To see which macros are defined, look for
<varname>CPLUSPLUS_CPP_SPEC</varname> in
the gcc config headers for your target (and try changing them to
see what happens when building complicated code). You can also run
that are required to allow the C++ library to work with your C library.
</para>
- <para>Several libstdc++ source files unconditionally define the macro
-<code>_POSIX_SOURCE</code>. On many systems, defining this macro causes
-large portions of the C library header files to be eliminated
-at preprocessing time. Therefore, you may have to <code>#undef</code> this
-macro, or define other macros (like <code>_LARGEFILE_SOURCE</code> or
-<code>__EXTENSIONS__</code>). You won't know what macros to define or
-undefine at this point; you'll have to try compiling the library and
-seeing what goes wrong. If you see errors about calling functions
-that have not been declared, look in your C library headers to see if
-the functions are declared there, and then figure out what macros you
-need to define. You will need to add them to the
-<code>CPLUSPLUS_CPP_SPEC</code> macro in the GCC configuration file for your
-target. It will not work to simply define these macros in
-<code>os_defines.h</code>.
- </para>
-
<para>At this time, there are a few libstdc++-specific macros which may be
defined:
</para>
projects / thirdparty / gcc.git / commitdiff
