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<a name="fwrite_002c-fwrite_005funlocked_002d_002d_002dwrite-array-elements"></a>
<h3 class="section">4.32 <code>fwrite</code>, <code>fwrite_unlocked</code>&mdash;write array elements</h3>
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<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdio.h&gt;
size_t fwrite(const void *restrict <var>buf</var>, size_t <var>size</var>,
    size_t <var>count</var>, FILE *restrict <var>fp</var>);

#define _BSD_SOURCE
#include &lt;stdio.h&gt;
size_t fwrite_unlocked(const void *restrict <var>buf</var>, size_t <var>size</var>,
    size_t <var>count</var>, FILE *restrict <var>fp</var>);

#include &lt;stdio.h&gt;
size_t _fwrite_r(struct _reent *<var>ptr</var>, const void *restrict <var>buf</var>, size_t <var>size</var>,
    size_t <var>count</var>, FILE *restrict <var>fp</var>);

#include &lt;stdio.h&gt;
size_t _fwrite_unlocked_r(struct _reent *<var>ptr</var>, const void *restrict <var>buf</var>, size_t <var>size</var>,
    size_t <var>count</var>, FILE *restrict <var>fp</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>fwrite</code> attempts to copy, starting from the memory location
<var>buf</var>, <var>count</var> elements (each of size <var>size</var>) into the file or
stream identified by <var>fp</var>.  <code>fwrite</code> may copy fewer elements than
<var>count</var> if an error intervenes.
</p>
<p><code>fwrite</code> also advances the file position indicator (if any) for
<var>fp</var> by the number of <em>characters</em> actually written.
</p>
<p><code>fwrite_unlocked</code> is a non-thread-safe version of <code>fwrite</code>.
<code>fwrite_unlocked</code> may only safely be used within a scope
protected by flockfile() (or ftrylockfile()) and funlockfile().  This
function may safely be used in a multi-threaded program if and only
if they are called while the invoking thread owns the (FILE *)
object, as is the case after a successful call to the flockfile() or
ftrylockfile() functions.  If threads are disabled, then
<code>fwrite_unlocked</code> is equivalent to <code>fwrite</code>.
</p>
<p><code>_fwrite_r</code> and <code>_fwrite_unlocked_r</code> are simply reentrant versions of the
above that take an additional reentrant structure argument: <var>ptr</var>.
</p>
<br>
<p><strong>Returns</strong><br>
If <code>fwrite</code> succeeds in writing all the elements you specify, the
result is the same as the argument <var>count</var>.  In any event, the
result is the number of complete elements that <code>fwrite</code> copied to
the file.
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>fwrite</code>.
</p>
<p><code>fwrite_unlocked</code> is a BSD extension also provided by GNU libc.
</p>
<p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>,
<code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
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