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从www.CppReference.com打包的C++参考手册

  <div class="name-format">
    putback
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  istream&amp; putback( char ch );
</pre>

  <p>The putback() function is used with input streams, and returns the
  previously-read character <em>ch</em> to the input stream.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="peek.html">peek</a><br>
    (Standard C I/O) <a href="../stdio/ungetc.html">ungetc</a>
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  <div class="name-format">
    rdstate
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  iostate rdstate();
</pre>

  <p>The rdstate() function returns the <a href=
  "../io_flags.html#state_flags">io stream state flag</a>s of the
  current stream.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="bad.html">bad</a><br>
    <a href="clear.html">clear</a><br>
    <a href="eof.html">eof</a><br>
    <a href="fail.html">fail</a><br>
    <a href="good.html">good</a>
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<hr>

  <div class="name-format">
    read
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  istream&amp; read( char* buffer, streamsize num );
</pre>

  <p>The function read() is used with input streams, and reads
  <em>num</em> bytes from the stream before placing them in
  <em>buffer</em>. If <strong>EOF</strong> is encountered, read()
  stops, leaving however many bytes it put into <em>buffer</em> as they
  are.</p>

  <p>For example:</p>
  <pre class="example-code">
   struct {
     int height;
     int width;
   } rectangle;         

   input_file.read( (char *)(&amp;rectangle), sizeof(rectangle) );
   if( input_file.bad() ) {
     cerr &lt;&lt; &quot;Error reading data&quot; &lt;&lt; endl;
     exit( 0 );
   }            
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="gcount.html">gcount</a><br>
    <a href="get.html">get</a><br>
    <a href="getline.html">getline</a><br>
    <a href="write.html">write</a>
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<hr>

  <div class="name-format">
    seekg
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  istream&amp; seekg( off_type offset, ios::seekdir origin );
  istream&amp; seekg( pos_type position );
</pre>

  <p>The function seekg() is used with input streams, and it
  repositions the &quot;get&quot; pointer for the current stream to
  <em>offset</em> bytes away from <em>origin</em>, or places the
  &quot;get&quot; pointer at <em>position</em>.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="seekp.html">seekp</a><br>
    <a href="tellg.html">tellg</a><br>
    <a href="tellp.html">tellp</a>
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<hr>

  <div class="name-format">
    seekp
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  ostream&amp; seekp( off_type offset, ios::seekdir origin );
  ostream&amp; seekp( pos_type position );
</pre>

  <p>The seekp() function is used with output streams, but is otherwise
  very similar to <a href="seekg.html">seekg</a>().</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="seekg.html">seekg</a><br>
    <a href="tellg.html">tellg</a><br>
    <a href="tellp.html">tellp</a>
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<hr>

  <div class="name-format">
    setf
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  fmtflags setf( fmtflags flags );
  fmtflags setf( fmtflags flags, fmtflags needed );
</pre>

  <p>The function setf() sets the <a href=
  "../io_flags.html#format_flags">io stream format flag</a>s of the
  current stream to <em>flags</em>. The optional <em>needed</em>
  argument specifies that only the flags that are in both
  <em>flags</em> and <em>needed</em> should be set. The return value is
  the previous configuration of <a href=
  "../io_flags.html#format_flags">io stream format flag</a>s.</p>

  <p>For example:</p>
  <pre class="example-code">
   int number = 0x3FF;
   cout.setf( ios::dec );
   cout &lt;&lt; &quot;Decimal: &quot; &lt;&lt; number &lt;&lt; endl;
   cout.unsetf( ios::dec );
   cout.setf( ios::hex );
   cout &lt;&lt; &quot;Hexadecimal: &quot; &lt;&lt; number &lt;&lt; endl;               
</pre>

  <p>Note that the preceding code is functionally identical to:</p>
  <pre class="example-code">
   int number = 0x3FF;
   cout &lt;&lt; &quot;Decimal: &quot; &lt;&lt; number &lt;&lt; endl &lt;&lt; hex &lt;&lt; &quot;Hexadecimal: &quot; &lt;&lt; number &lt;&lt; dec &lt;&lt; endl;                
</pre>

  <p>thanks to <a href="../io_flags.html#manipulators">io stream
  manipulator</a>s.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="flags.html">flags</a><br>
    <a href="unsetf.html">unsetf</a>
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<hr>

  <div class="name-format">
    sync_with_stdio
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  static bool sync_with_stdio( bool sync=true );
</pre>

  <p>The sync_with_stdio() function allows you to turn on and off the
  ability for the C++ I/O system to work with the C I/O system.</p>
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<hr>

  <div class="name-format">
    tellg
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  pos_type tellg();
</pre>

  <p>The tellg() function is used with input streams, and returns the
  current &quot;get&quot; position of the pointer in the stream.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="seekg.html">seekg</a><br>
    <a href="seekp.html">seekp</a><br>
    <a href="tellp.html">tellp</a>
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<hr>

  <div class="name-format">
    tellp
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  pos_type tellp();
</pre>

  <p>The tellp() function is used with output streams, and returns the
  current &quot;put&quot; position of the pointer in the stream.</p>

  <p>For example, the following code displays the file pointer as it
  writes to a stream:</p>
  <pre class="example-code">
 string s(&quot;In Xanadu did Kubla Khan...&quot;);
 ofstream fout(&quot;output.txt&quot;);
 for( int i=0; i &lt; s.length(); i++ ) {
   cout &lt;&lt; &quot;File pointer: &quot; &lt;&lt; fout.tellp();
   fout.put( s[i] );
   cout &lt;&lt; &quot; &quot; &lt;&lt; s[i] &lt;&lt; endl;
 }
 fout.close();          
</pre>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="seekg.html">seekg</a><br>
    <a href="seekp.html">seekp</a><br>
    <a href="tellg.html">tellg</a>
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<hr>

  <div class="name-format">
    unsetf
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  void unsetf( fmtflags flags );
</pre>

  <p>The function unsetf() uses <em>flags</em> to clear the <a href=
  "../io_flags.html#format_flags">io stream format flag</a>s associated
  with the current stream.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="flags.html">flags</a><br>
    <a href="setf.html">setf</a>
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<hr>

  <div class="name-format">
    width
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  int width();
  int width( int w );
</pre>

  <p>The function width() returns the current width, which is defined
  as the minimum number of characters to display with each output. The
  optional argument <em>w</em> can be used to set the width.</p>

  <p>For example:</p>
  <pre class="example-code">
   cout.width( 5 );
   cout &lt;&lt; &quot;2&quot;;         
</pre>

  <p>displays</p>
  <pre class="example-code">
       2                
</pre>

  <p>(that&#39;s four spaces followed by a &#39;2&#39;)</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="fill.html">fill</a><br>
    <a href="precision.html">precision</a>
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<hr>

  <div class="name-format">
    write
  </div>

  <div class="syntax-name-format">
    Syntax:
  </div>
  <pre class="syntax-box">
  #include &lt;fstream&gt;
  ostream&amp; write( const char* buffer, streamsize num );
</pre>

  <p>The write() function is used with output streams, and writes
  <em>num</em> bytes from <em>buffer</em> to the current output
  stream.</p>

  <div class="related-name-format">
    Related topics:
  </div>

  <div class="related-content">
    <a href="flush.html">flush</a><br>
    <a href="put.html">put</a><br>
    <a href="read.html">read</a>
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