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eof [C++ Reference]
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<h2><a name="eof" id="eof">eof</a></h2>
<div class="level2">
<p>
Syntax:
</p>
<pre class="c code c++" style="font-family:monospace;"> bool istream<span class="sy0">::</span><span class="me2">eof</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">;</span></pre>
<p>
The function eof() returns true if the end of the associated input file has been reached, false otherwise.
</p>
<p>
A stream goes into <acronym title="End of file">EOF</acronym> state whenever the end of stream is seen, i.e. a character past the end has been read. As operator» and <a href="../io/getline.html" class="wikilink1" title="io:getline">getline</a> normally keep reading characters until the end of token (until whitespace, invalid characters, line terminator or <acronym title="End of file">EOF</acronym>) it is possible that the stream <acronym title="End of file">EOF</acronym> flag gets set even though the token was read correctly. Conversely, the stream does not go into <acronym title="End of file">EOF</acronym> state if there happens to be any whitespace after the last token, but trying to read another token will still fail.
</p>
<p>
Therefore, the <acronym title="End of file">EOF</acronym> flag <strong>cannot</strong> be used as a test in a loop intended to read all stream contents until <acronym title="End of file">EOF</acronym>.
</p>
<p>
Instead, one should check for the fail condition after an attempt to read. This is done most conveniently by testing the stream itself, as follows:
</p>
<pre class="c code c++" style="font-family:monospace;"> std<span class="sy0">::</span><span class="me2">ifstream</span> file<span class="br0">(</span><span class="st0">"test.txt"</span><span class="br0">)</span><span class="sy0">;</span>
std<span class="sy0">::</span><span class="kw4">string</span> line<span class="sy0">;</span>
<span class="kw1">while</span> <span class="br0">(</span>std<span class="sy0">::</span><span class="me2">getline</span><span class="br0">(</span>file<span class="sy0">,</span> line<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
<span class="co1">// A line was read successfully, so you can process it</span>
<span class="br0">}</span></pre>
<p>
Line 7 of the example below illustrates the main use for checking the <acronym title="End of file">EOF</acronym> state: after a failed read. In such a situation, it can be used to determine whether or not the fail was caused by reaching the end of stream.
</p>
<pre class="c code c++" style="font-family:monospace;"><span class="lno">1:</span> std<span class="sy0">::</span><span class="me2">ifstream</span> file<span class="br0">(</span><span class="st0">"test.txt"</span><span class="br0">)</span><span class="sy0">;</span>
<span class="lno">2:</span> std<span class="sy0">::</span><span class="kw4">string</span> word<span class="sy0">;</span>
<span class="lno">3:</span> <span class="kw4">double</span> value<span class="sy0">;</span>
<span class="lno">4:</span> <span class="kw1">while</span> <span class="br0">(</span>file <span class="sy0">>></span> word <span class="sy0">>></span> value<span class="br0">)</span> <span class="br0">{</span>
<span class="lno">5:</span> <span class="co1">// A word and a double value were both read successfully</span>
<span class="lno">6:</span> <span class="br0">}</span>
<span class="lno">7:</span> <span class="kw1">if</span> <span class="br0">(</span><span class="sy0">!</span>file.<span class="me1">eof</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> throw std<span class="sy0">::</span><span class="me2">runtime_error</span><span class="br0">(</span><span class="st0">"Invalid data from file"</span><span class="br0">)</span><span class="sy0">;</span>
</pre>
<p>
The table below lists a number of different states that a stream may be in:
</p>
<table class="inline">
<tr class="row0">
<th class="col0">Test</th><th class="col1">Description</th>
</tr>
<tr class="row1">
<td class="col0">if (s)</td><td class="col1">The previous operation was successful (a shorthand for !s.fail()).</td>
</tr>
<tr class="row2">
<td class="col0">if (s.fail())</td><td class="col1">The previous operation failed.</td>
</tr>
<tr class="row3">
<td class="col0">if (s.eof())</td><td class="col1">Reading past the end has been attempted.</td>
</tr>
<tr class="row4">
<td class="col0">if (s.bad())</td><td class="col1">Stream state is undefined; the stream can no longer be used.</td>
</tr>
<tr class="row5">
<td class="col0">if (s.good())</td><td class="col1">None of bad/eof/fail are set.</td>
</tr>
</table>
<p>
Related Topics: <a href="../io/bad.html" class="wikilink1" title="io:bad">bad</a>, <a href="../io/clear.html" class="wikilink1" title="io:clear">clear</a>, <a href="../io/exceptions.html" class="wikilink1" title="io:exceptions">exceptions</a>, <a href="../io/fail.html" class="wikilink1" title="io:fail">fail</a>, <a href="../io/good.html" class="wikilink1" title="io:good">good</a>, <a href="../io/rdstate.html" class="wikilink1" title="io:rdstate">rdstate</a>
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