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| <h3 class="section">4.66 <code>ungetc</code>—push data back into a stream</h3> |
| |
| <p><a name="index-ungetc-321"></a><a name="index-g_t_005fungetc_005fr-322"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <stdio.h> |
| 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> |
| <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>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>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> |
| <strong>Returns</strong><br> |
| The character pushed back, or <code>EOF</code> on error. |
| |
| <p><br> |
| <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>Supporting OS subroutines required: <code>sbrk</code>. |
| |
| <p><br> |
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