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105 lines
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105 lines
4.2 KiB
HTML
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<a name="ungetc"></a>
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<div class="header">
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<p>
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Next: <a href="ungetwc.html#ungetwc" accesskey="n" rel="next">ungetwc</a>, Previous: <a href="tmpnam.html#tmpnam" accesskey="p" rel="prev">tmpnam</a>, Up: <a href="Stdio.html#Stdio" accesskey="u" rel="up">Stdio</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="ungetc_002d_002d_002dpush-data-back-into-a-stream"></a>
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<h3 class="section">4.68 <code>ungetc</code>—push data back into a stream</h3>
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<a name="index-ungetc"></a>
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<a name="index-_005fungetc_005fr"></a>
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<p><strong>Synopsis</strong>
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</p><div class="example">
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<pre class="example">#include <stdio.h>
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int ungetc(int <var>c</var>, FILE *<var>stream</var>);
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int _ungetc_r(struct _reent *<var>reent</var>, int <var>c</var>, FILE *<var>stream</var>);
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</pre></div>
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<p><strong>Description</strong><br>
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<code>ungetc</code> is used to return bytes back to <var>stream</var> to be read again.
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If <var>c</var> is EOF, the stream is unchanged. Otherwise, the unsigned
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char <var>c</var> is put back on the stream, and subsequent reads will see
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the bytes pushed back in reverse order. Pushed byes are lost if the
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stream is repositioned, such as by <code>fseek</code>, <code>fsetpos</code>, or
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<code>rewind</code>.
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</p>
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<p>The underlying file is not changed, but it is possible to push back
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something different than what was originally read. Ungetting a
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character will clear the end-of-stream marker, and decrement the file
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position indicator. Pushing back beyond the beginning of a file gives
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unspecified behavior.
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</p>
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<p>The alternate function <code>_ungetc_r</code> is a reentrant version. The
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extra argument <var>reent</var> is a pointer to a reentrancy structure.
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</p>
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<br>
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<p><strong>Returns</strong><br>
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The character pushed back, or <code>EOF</code> on error.
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</p>
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<br>
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<p><strong>Portability</strong><br>
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ANSI C requires <code>ungetc</code>, but only requires a pushback buffer of one
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byte; although this implementation can handle multiple bytes, not all
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can. Pushing back a signed char is a common application bug.
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</p>
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<p>Supporting OS subroutines required: <code>sbrk</code>.
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</p>
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<br>
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