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| <a name="String-Parameters"></a> |
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| <h3 class="section">31.12 String-Valued Parameters</h3> |
| |
| <p>POSIX.2 defines a way to get string-valued parameters from the operating |
| system with the function <code>confstr</code>: |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Function: size_t <b>confstr</b> (<var>int parameter, char *buf, size_t len</var>)<var><a name="index-confstr-3675"></a></var><br> |
| <blockquote><p>This function reads the value of a string-valued system parameter, |
| storing the string into <var>len</var> bytes of memory space starting at |
| <var>buf</var>. The <var>parameter</var> argument should be one of the |
| ‘<samp><span class="samp">_CS_</span></samp>’ symbols listed below. |
| |
| <p>The normal return value from <code>confstr</code> is the length of the string |
| value that you asked for. If you supply a null pointer for <var>buf</var>, |
| then <code>confstr</code> does not try to store the string; it just returns |
| its length. A value of <code>0</code> indicates an error. |
| |
| <p>If the string you asked for is too long for the buffer (that is, longer |
| than <var>len</var><code> - 1</code>), then <code>confstr</code> stores just that much |
| (leaving room for the terminating null character). You can tell that |
| this has happened because <code>confstr</code> returns a value greater than or |
| equal to <var>len</var>. |
| |
| <p>The following <code>errno</code> error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EINVAL</code><dd>The value of the <var>parameter</var> is invalid. |
| </dl> |
| </p></blockquote></div> |
| |
| <p>Currently there is just one parameter you can read with <code>confstr</code>: |
| |
| <dl> |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <dt><code>_CS_PATH</code><dd>This parameter's value is the recommended default path for searching for |
| executable files. This is the path that a user has by default just |
| after logging in. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS_CFLAGS</code><dd>The returned string specifies which additional flags must be given to |
| the C compiler if a source is compiled using the |
| <code>_LARGEFILE_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS_LDFLAGS</code><dd>The returned string specifies which additional flags must be given to |
| the linker if a source is compiled using the |
| <code>_LARGEFILE_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS_LIBS</code><dd>The returned string specifies which additional libraries must be linked |
| to the application if a source is compiled using the |
| <code>_LARGEFILE_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS_LINTFLAGS</code><dd>The returned string specifies which additional flags must be given to |
| the lint tool if a source is compiled using the |
| <code>_LARGEFILE_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS64_CFLAGS</code><dd>The returned string specifies which additional flags must be given to |
| the C compiler if a source is compiled using the |
| <code>_LARGEFILE64_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS64_LDFLAGS</code><dd>The returned string specifies which additional flags must be given to |
| the linker if a source is compiled using the |
| <code>_LARGEFILE64_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS64_LIBS</code><dd>The returned string specifies which additional libraries must be linked |
| to the application if a source is compiled using the |
| <code>_LARGEFILE64_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| |
| <!-- unistd.h --> |
| <!-- Unix98 --> |
| <br><dt><code>_CS_LFS64_LINTFLAGS</code><dd>The returned string specifies which additional flags must be given to |
| the lint tool if a source is compiled using the |
| <code>_LARGEFILE64_SOURCE</code> feature select macro; see <a href="Feature-Test-Macros.html#Feature-Test-Macros">Feature Test Macros</a>. |
| </dl> |
| |
| <p>The way to use <code>confstr</code> without any arbitrary limit on string size |
| is to call it twice: first call it to get the length, allocate the |
| buffer accordingly, and then call <code>confstr</code> again to fill the |
| buffer, like this: |
| |
| <pre class="smallexample"> char * |
| get_default_path (void) |
| { |
| size_t len = confstr (_CS_PATH, NULL, 0); |
| char *buffer = (char *) xmalloc (len); |
| |
| if (confstr (_CS_PATH, buf, len + 1) == 0) |
| { |
| free (buffer); |
| return NULL; |
| } |
| |
| return buffer; |
| } |
| </pre> |
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