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<a name="ungetc_002d_002d_002dpush-data-back-into-a-stream"></a>
<h3 class="section">4.68 <code>ungetc</code>&mdash;push data back into a stream</h3>
<a name="index-ungetc"></a>
<a name="index-_005fungetc_005fr"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdio.h&gt;
int ungetc(int <var>c</var>, FILE *<var>stream</var>);

int _ungetc_r(struct _reent *<var>reent</var>, int <var>c</var>, FILE *<var>stream</var>);

</pre></div>
<p><strong>Description</strong><br>
<code>ungetc</code> is used to return bytes back to <var>stream</var> to be read again.
If <var>c</var> is EOF, the stream is unchanged.  Otherwise, the unsigned
char <var>c</var> is put back on the stream, and subsequent reads will see
the bytes pushed back in reverse order.  Pushed byes are lost if the
stream is repositioned, such as by <code>fseek</code>, <code>fsetpos</code>, or
<code>rewind</code>.
</p>
<p>The underlying file is not changed, but it is possible to push back
something different than what was originally read.  Ungetting a
character will clear the end-of-stream marker, and decrement the file
position indicator.  Pushing back beyond the beginning of a file gives
unspecified behavior.
</p>
<p>The alternate function <code>_ungetc_r</code> is a reentrant version.  The
extra argument <var>reent</var> is a pointer to a reentrancy structure.
</p>
<br>
<p><strong>Returns</strong><br>
The character pushed back, or <code>EOF</code> on error.
</p>
<br>
<p><strong>Portability</strong><br>
ANSI C requires <code>ungetc</code>, but only requires a pushback buffer of one
byte; although this implementation can handle multiple bytes, not all
can.  Pushing back a signed char is a common application bug.
</p>
<p>Supporting OS subroutines required: <code>sbrk</code>.
</p>
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