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<span id="EOF-and-Errors"></span><div class="header">
<p>
Next: <a href="File-Positioning.html" accesskey="n" rel="next">File Positioning</a>, Previous: <a href="Temporary-Files.html" accesskey="p" rel="prev">Temporary Files</a>, Up: <a href="C_002dStyle-I_002fO-Functions.html" accesskey="u" rel="up">C-Style I/O Functions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<span id="End-of-File-and-Errors"></span><h4 class="subsection">14.2.18 End of File and Errors</h4>
<p>Once a file has been opened its status can be acquired. As an example
the <code>feof</code> functions determines if the end of the file has been
reached. This can be very useful when reading small parts of a file
at a time. The following example shows how to read one line at a time
from a file until the end has been reached.
</p>
<div class="example">
<pre class="example">filename = "myfile.txt";
fid = fopen (filename, "r");
while (! feof (fid) )
text_line = fgetl (fid);
endwhile
fclose (fid);
</pre></div>
<p>Note that in some situations it is more efficient to read the entire
contents of a file and then process it, than it is to read it line by
line. This has the potential advantage of removing the loop in the
above code.
</p>
<span id="XREFfeof"></span><dl>
<dt id="index-feof">: <em><var>status</var> =</em> <strong>feof</strong> <em>(<var>fid</var>)</em></dt>
<dd><p>Return 1 if an end-of-file condition has been encountered for the file
specified by file descriptor <var>fid</var> and 0 otherwise.
</p>
<p>Note that <code>feof</code> will only return 1 if the end of the file has already
been encountered, not if the next read operation will result in an
end-of-file condition.
</p>
<p><strong>See also:</strong> <a href="Binary-I_002fO.html#XREFfread">fread</a>, <a href="File-Positioning.html#XREFfrewind">frewind</a>, <a href="File-Positioning.html#XREFfseek">fseek</a>, <a href="#XREFfclear">fclear</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<span id="XREFferror"></span><dl>
<dt id="index-ferror">: <em><var>msg</var> =</em> <strong>ferror</strong> <em>(<var>fid</var>)</em></dt>
<dt id="index-ferror-1">: <em>[<var>msg</var>, <var>err</var>] =</em> <strong>ferror</strong> <em>(<var>fid</var>)</em></dt>
<dt id="index-ferror-2">: <em>[…] =</em> <strong>ferror</strong> <em>(<var>fid</var>, "clear")</em></dt>
<dd><p>Query the error status of the stream specified by file descriptor <var>fid</var>.
</p>
<p>If an error condition exists then return a string <var>msg</var> describing the
error. Otherwise, return an empty string <code>""</code>.
</p>
<p>The second input <code>"clear"</code> is optional. If supplied, the error
state on the stream will be cleared.
</p>
<p>The optional second output is a numeric indication of the error status.
<var>err</var> is 1 if an error condition has been encountered and 0 otherwise.
</p>
<p>Note that <code>ferror</code> indicates if an error has already occurred, not
whether the next operation will result in an error condition.
</p>
<p><strong>See also:</strong> <a href="#XREFfclear">fclear</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<span id="XREFfclear"></span><dl>
<dt id="index-fclear">: <em></em> <strong>fclear</strong> <em>(<var>fid</var>)</em></dt>
<dd><p>Clear the stream state for the file specified by the file descriptor
<var>fid</var>.
</p>
<p><strong>See also:</strong> <a href="#XREFferror">ferror</a>, <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<span id="XREFfreport"></span><dl>
<dt id="index-freport">: <em></em> <strong>freport</strong> <em>()</em></dt>
<dd><p>Print a list of which files have been opened, and whether they are open
for reading, writing, or both.
</p>
<p>For example:
</p>
<div class="example">
<pre class="example">freport ()
-| number mode arch name
-| ------ ---- ---- ----
-| 0 r ieee-le stdin
-| 1 w ieee-le stdout
-| 2 w ieee-le stderr
-| 3 r ieee-le myfile
</pre></div>
<p><strong>See also:</strong> <a href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>, <a href="Opening-and-Closing-Files.html#XREFfclose">fclose</a>, <a href="Opening-and-Closing-Files.html#XREFis_005fvalid_005ffile_005fid">is_valid_file_id</a>.
</p></dd></dl>
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