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| <h3 class="section">31.3 Which Version of POSIX is Supported</h3> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: long int <b>_POSIX_VERSION</b><var><a name="index-g_t_005fPOSIX_005fVERSION-3522"></a></var><br> |
| <blockquote><p>This constant represents the version of the POSIX.1 standard to which |
| the implementation conforms. For an implementation conforming to the |
| 1995 POSIX.1 standard, the value is the integer <code>199506L</code>. |
| |
| <p><code>_POSIX_VERSION</code> is always defined (in <samp><span class="file">unistd.h</span></samp>) in any |
| POSIX system. |
| |
| <p><strong>Usage Note:</strong> Don't try to test whether the system supports POSIX |
| by including <samp><span class="file">unistd.h</span></samp> and then checking whether |
| <code>_POSIX_VERSION</code> is defined. On a non-POSIX system, this will |
| probably fail because there is no <samp><span class="file">unistd.h</span></samp>. We do not know of |
| <em>any</em> way you can reliably test at compilation time whether your |
| target system supports POSIX or whether <samp><span class="file">unistd.h</span></samp> exists. |
| |
| <p>The GNU C compiler predefines the symbol <code>__POSIX__</code> if the target |
| system is a POSIX system. Provided you do not use any other compilers |
| on POSIX systems, testing <code>defined (__POSIX__)</code> will reliably |
| detect such systems. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Macro: long int <b>_POSIX2_C_VERSION</b><var><a name="index-g_t_005fPOSIX2_005fC_005fVERSION-3523"></a></var><br> |
| <blockquote><p>This constant represents the version of the POSIX.2 standard which the |
| library and system kernel support. We don't know what value this will |
| be for the first version of the POSIX.2 standard, because the value is |
| based on the year and month in which the standard is officially adopted. |
| |
| <p>The value of this symbol says nothing about the utilities installed on |
| the system. |
| |
| <p><strong>Usage Note:</strong> You can use this macro to tell whether a POSIX.1 |
| system library supports POSIX.2 as well. Any POSIX.1 system contains |
| <samp><span class="file">unistd.h</span></samp>, so include that file and then test <code>defined |
| (_POSIX2_C_VERSION)</code>. |
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