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<h4 class="subsection" id="End-of-File-and-Errors"><span>14.2.18 End of File and Errors<a class="copiable-link" href="#End-of-File-and-Errors"> ¶</a></span></h4>
<p>Once a file has been opened its status can be acquired. As an example
the <code class="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">
<div class="group"><pre class="example-preformatted">filename = "myfile.txt";
fid = fopen (filename, "r");
while (! feof (fid) )
text_line = fgetl (fid);
endwhile
fclose (fid);
</pre></div></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>
<a class="anchor" id="XREFfeof"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-feof"><span><code class="def-type"><var class="var">status</var> =</code> <strong class="def-name">feof</strong> <code class="def-code-arguments">(<var class="var">fid</var>)</code><a class="copiable-link" href="#index-feof"> ¶</a></span></dt>
<dd><p>Return 1 if an end-of-file condition has been encountered for the file
specified by file descriptor <var class="var">fid</var> and 0 otherwise.
</p>
<p>Note that <code class="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 class="strong">See also:</strong> <a class="ref" href="Binary-I_002fO.html#XREFfread">fread</a>, <a class="ref" href="File-Positioning.html#XREFfrewind">frewind</a>, <a class="ref" href="File-Positioning.html#XREFfseek">fseek</a>, <a class="ref" href="#XREFfclear">fclear</a>, <a class="ref" href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<a class="anchor" id="XREFferror"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-ferror"><span><code class="def-type"><var class="var">msg</var> =</code> <strong class="def-name">ferror</strong> <code class="def-code-arguments">(<var class="var">fid</var>)</code><a class="copiable-link" href="#index-ferror"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-ferror-1"><span><code class="def-type">[<var class="var">msg</var>, <var class="var">err</var>] =</code> <strong class="def-name">ferror</strong> <code class="def-code-arguments">(<var class="var">fid</var>)</code><a class="copiable-link" href="#index-ferror-1"> ¶</a></span></dt>
<dt class="deftypefnx def-cmd-deftypefn" id="index-ferror-2"><span><code class="def-type">[…] =</code> <strong class="def-name">ferror</strong> <code class="def-code-arguments">(<var class="var">fid</var>, "clear")</code><a class="copiable-link" href="#index-ferror-2"> ¶</a></span></dt>
<dd><p>Query the error status of the stream specified by file descriptor <var class="var">fid</var>.
</p>
<p>If an error condition exists then return a string <var class="var">msg</var> describing the
error. Otherwise, return an empty string <code class="code">""</code>.
</p>
<p>The second input <code class="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 class="var">err</var> is 1 if an error condition has been encountered and 0 otherwise.
</p>
<p>Note that <code class="code">ferror</code> indicates if an error has already occurred, not
whether the next operation will result in an error condition.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFfclear">fclear</a>, <a class="ref" href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<a class="anchor" id="XREFfclear"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-fclear"><span><strong class="def-name">fclear</strong> <code class="def-code-arguments">(<var class="var">fid</var>)</code><a class="copiable-link" href="#index-fclear"> ¶</a></span></dt>
<dd><p>Clear the stream state for the file specified by the file descriptor
<var class="var">fid</var>.
</p>
<p><strong class="strong">See also:</strong> <a class="ref" href="#XREFferror">ferror</a>, <a class="ref" href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>.
</p></dd></dl>
<a class="anchor" id="XREFfreport"></a><span style="display:block; margin-top:-4.5ex;"> </span>
<dl class="first-deftypefn">
<dt class="deftypefn" id="index-freport"><span><strong class="def-name">freport</strong> <code class="def-code-arguments">()</code><a class="copiable-link" href="#index-freport"> ¶</a></span></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">
<div class="group"><pre class="example-preformatted">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></div>
<p><strong class="strong">See also:</strong> <a class="ref" href="Opening-and-Closing-Files.html#XREFfopen">fopen</a>, <a class="ref" href="Opening-and-Closing-Files.html#XREFfclose">fclose</a>, <a class="ref" href="Opening-and-Closing-Files.html#XREFis_005fvalid_005ffile_005fid">is_valid_file_id</a>.
</p></dd></dl>
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