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<a name="tmpnam_002c-tempnam_002d_002d_002dname-for-a-temporary-file"></a>
<h3 class="section">4.67 <code>tmpnam</code>, <code>tempnam</code>&mdash;name for a temporary file</h3>
<a name="index-tmpnam"></a>
<a name="index-tempnam"></a>
<a name="index-_005ftmpnam_005fr"></a>
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<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdio.h&gt;
char *tmpnam(char *<var>s</var>);
char *tempnam(char *<var>dir</var>, char *<var>pfx</var>);
char *_tmpnam_r(struct _reent *<var>reent</var>, char *<var>s</var>);
char *_tempnam_r(struct _reent *<var>reent</var>, char *<var>dir</var>, char *<var>pfx</var>);

</pre></div>
<p><strong>Description</strong><br>
Use either of these functions to generate a name for a temporary file.
The generated name is guaranteed to avoid collision with other files
(for up to <code>TMP_MAX</code> calls of either function).
</p>
<p><code>tmpnam</code> generates file names with the value of <code>P_tmpdir</code>
(defined in &lsquo;<code>stdio.h</code>&rsquo;) as the leading directory component of the path.
</p>
<p>You can use the <code>tmpnam</code> argument <var>s</var> to specify a suitable area
of memory for the generated filename; otherwise, you can call
<code>tmpnam(NULL)</code> to use an internal static buffer.
</p>
<p><code>tempnam</code> allows you more control over the generated filename: you
can use the argument <var>dir</var> to specify the path to a directory for
temporary files, and you can use the argument <var>pfx</var> to specify a
prefix for the base filename.
</p>
<p>If <var>dir</var> is <code>NULL</code>, <code>tempnam</code> will attempt to use the value of
environment variable <code>TMPDIR</code> instead; if there is no such value,
<code>tempnam</code> uses the value of <code>P_tmpdir</code> (defined in &lsquo;<code>stdio.h</code>&rsquo;).
</p>
<p>If you don&rsquo;t need any particular prefix to the basename of temporary
files, you can pass <code>NULL</code> as the <var>pfx</var> argument to <code>tempnam</code>.
</p>
<p><code>_tmpnam_r</code> and <code>_tempnam_r</code> are reentrant versions of <code>tmpnam</code>
and <code>tempnam</code> respectively.  The extra argument <var>reent</var> is a
pointer to a reentrancy structure.
</p>
<br>
<p><strong>Warnings</strong><br>
The generated filenames are suitable for temporary files, but do not
in themselves make files temporary.  Files with these names must still
be explicitly removed when you no longer want them.
</p>
<p>If you supply your own data area <var>s</var> for <code>tmpnam</code>, you must ensure
that it has room for at least <code>L_tmpnam</code> elements of type <code>char</code>.
</p>
<br>
<p><strong>Returns</strong><br>
Both <code>tmpnam</code> and <code>tempnam</code> return a pointer to the newly
generated filename.
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>tmpnam</code>, but does not specify the use of
<code>P_tmpdir</code>.  The System V Interface Definition (Issue 2) requires
both <code>tmpnam</code> and <code>tempnam</code>.
</p>
<p>Supporting OS subroutines required: <code>close</code>,  <code>fstat</code>, <code>getpid</code>,
<code>isatty</code>, <code>lseek</code>, <code>open</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
</p>
<p>The global pointer <code>environ</code> is also required.
</p>
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