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<a name="ferror_002c-ferror_005funlocked_002d_002d_002dtest-whether-read_002fwrite-error-has-occurred"></a>
<h3 class="section">4.8 <code>ferror</code>, <code>ferror_unlocked</code>—test whether read/write error has occurred</h3>
<a name="index-ferror"></a>
<a name="index-ferror_005funlocked"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include <stdio.h>
int ferror(FILE *<var>fp</var>);
#define _BSD_SOURCE
#include <stdio.h>
int ferror_unlocked(FILE *<var>fp</var>);
</pre></div>
<p><strong>Description</strong><br>
The <code>stdio</code> functions maintain an error indicator with each file
pointer <var>fp</var>, to record whether any read or write errors have
occurred on the associated file or stream.
Use <code>ferror</code> to query this indicator.
</p>
<p>See <code>clearerr</code> to reset the error indicator.
</p>
<p><code>ferror_unlocked</code> is a non-thread-safe version of <code>ferror</code>.
<code>ferror_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>ferror_unlocked</code> is equivalent to <code>ferror</code>.
</p>
<br>
<p><strong>Returns</strong><br>
<code>ferror</code> returns <code>0</code> if no errors have occurred; it returns a
nonzero value otherwise.
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>ferror</code>.
</p>
<p><code>ferror_unlocked</code> is a BSD extension also provided by GNU libc.
</p>
<p>No supporting OS subroutines are required.
</p>
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