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| <h3 class="section">12.15 End-Of-File and Errors</h3> |
| |
| <p><a name="index-end-of-file_002c-on-a-stream-1095"></a>Many of the functions described in this chapter return the value of the |
| macro <code>EOF</code> to indicate unsuccessful completion of the operation. |
| Since <code>EOF</code> is used to report both end of file and random errors, |
| it's often better to use the <code>feof</code> function to check explicitly |
| for end of file and <code>ferror</code> to check for errors. These functions |
| check indicators that are part of the internal state of the stream |
| object, indicators set if the appropriate condition was detected by a |
| previous I/O operation on that stream. |
| |
| <!-- stdio.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>EOF</b><var><a name="index-EOF-1096"></a></var><br> |
| <blockquote><p>This macro is an integer value that is returned by a number of narrow |
| stream functions to indicate an end-of-file condition, or some other |
| error situation. With the GNU library, <code>EOF</code> is <code>-1</code>. In |
| other libraries, its value may be some other negative number. |
| |
| <p>This symbol is declared in <samp><span class="file">stdio.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- wchar.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>WEOF</b><var><a name="index-WEOF-1097"></a></var><br> |
| <blockquote><p>This macro is an integer value that is returned by a number of wide |
| stream functions to indicate an end-of-file condition, or some other |
| error situation. With the GNU library, <code>WEOF</code> is <code>-1</code>. In |
| other libraries, its value may be some other negative number. |
| |
| <p>This symbol is declared in <samp><span class="file">wchar.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: int <b>feof</b> (<var>FILE *stream</var>)<var><a name="index-feof-1098"></a></var><br> |
| <blockquote><p>The <code>feof</code> function returns nonzero if and only if the end-of-file |
| indicator for the stream <var>stream</var> is set. |
| |
| <p>This symbol is declared in <samp><span class="file">stdio.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: int <b>feof_unlocked</b> (<var>FILE *stream</var>)<var><a name="index-feof_005funlocked-1099"></a></var><br> |
| <blockquote><p>The <code>feof_unlocked</code> function is equivalent to the <code>feof</code> |
| function except that it does not implicitly lock the stream. |
| |
| <p>This function is a GNU extension. |
| |
| <p>This symbol is declared in <samp><span class="file">stdio.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Function: int <b>ferror</b> (<var>FILE *stream</var>)<var><a name="index-ferror-1100"></a></var><br> |
| <blockquote><p>The <code>ferror</code> function returns nonzero if and only if the error |
| indicator for the stream <var>stream</var> is set, indicating that an error |
| has occurred on a previous operation on the stream. |
| |
| <p>This symbol is declared in <samp><span class="file">stdio.h</span></samp>. |
| </p></blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: int <b>ferror_unlocked</b> (<var>FILE *stream</var>)<var><a name="index-ferror_005funlocked-1101"></a></var><br> |
| <blockquote><p>The <code>ferror_unlocked</code> function is equivalent to the <code>ferror</code> |
| function except that it does not implicitly lock the stream. |
| |
| <p>This function is a GNU extension. |
| |
| <p>This symbol is declared in <samp><span class="file">stdio.h</span></samp>. |
| </p></blockquote></div> |
| |
| <p>In addition to setting the error indicator associated with the stream, |
| the functions that operate on streams also set <code>errno</code> in the same |
| way as the corresponding low-level functions that operate on file |
| descriptors. For example, all of the functions that perform output to a |
| stream—such as <code>fputc</code>, <code>printf</code>, and <code>fflush</code>—are |
| implemented in terms of <code>write</code>, and all of the <code>errno</code> error |
| conditions defined for <code>write</code> are meaningful for these functions. |
| For more information about the descriptor-level I/O functions, see |
| <a href="Low_002dLevel-I_002fO.html#Low_002dLevel-I_002fO">Low-Level I/O</a>. |
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