ceph/src/boost/libs/iostreams/doc/functions/get.html

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   4     <TITLE>Function Template get</TITLE>
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  12     <H1 CLASS="title">Function Template <CODE>get</CODE></H1>
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  17 <DL class="page-index">
  18   <DT><A href="#overview">Overview</A></DT>
  19   <DT><A href="#example">Example</A></DT>
  20   <DT><A href="#headers">Headers</A></DT>
  21   <DT><A href="#reference">Reference</A></DT>
  22 </DL>
  23
  24 <A NAME="overview"></A>
  25 <H2>Overview</H2>
  26
  27 <P>
  28     The function template <CODE>get</CODE> provides a uniform interface for reading a character from a <A HREF="../concepts/source.html">Source</A>, for use in the definitions of new <A HREF="../guide/concepts.html#filter_concepts">Filter</A> types (<I>see</I> <A HREF="#example">Example</A>).
  29 </P>
  30
  31 <A NAME="example"></A>
  32 <H2>Example</H2>
  33
  34 <P>
  35     The following code illustrates the use of the function <CODE>get</CODE> in the definition of an <A HREF="../concepts/input_filter.html">InputFilter</A>.
  36 </P>
  37
  38 <PRE CLASS="broken_ie">    <SPAN CLASS="preprocessor">#include</SPAN> <SPAN CLASS="literal">&lt;ctype.h&gt;</SPAN>                        <SPAN CLASS="comment">// tolower</SPAN>
  39     <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/concepts.hpp"><SPAN CLASS="literal">&lt;boost/iostreams/concepts.hpp&gt;</SPAN></A>   <SPAN CLASS="comment">// input_filter</SPAN>
  40     <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><SPAN CLASS="literal">&lt;boost/iostreams/operations.hpp&gt;</SPAN></A> <SPAN CLASS="comment">// get, EOF, WOULD_BLOCK</SPAN>
  41
  42     <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> std;
  43     <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> boost::io;
  44
  45     <SPAN CLASS="keyword">struct</SPAN> tolower_filter : <SPAN CLASS="keyword">public</SPAN> input_filter {
  46         <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Source&gt;
  47         <SPAN CLASS="keyword">int</SPAN> get(Source&amp; src)
  48         {
  49             <SPAN CLASS="keyword">int</SPAN> c;
  50             <SPAN CLASS="keyword">return</SPAN> (c = boost::iostreams::get(src)) != <SPAN CLASS='numeric_literal'>EOF</SPAN> &amp;&amp;
  51                     c != WOULD_BLOCK
  52                         ?
  53                 tolower((<SPAN CLASS="keyword">unsigned</SPAN> <SPAN CLASS="keyword">char</SPAN>) c) :
  54                 c;
  55         }
  56     };</PRE>
  57
  58 <A NAME="headers"></A>
  59 <H2>Headers</H2>
  60
  61 <DL>
  62   <DT><A CLASS="header" HREF="../../../../boost/iostreams/get.hpp"><CODE>&lt;boost/iostreams/get.hpp&gt;</CODE></A></DT>
  63   <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE>&lt;boost/iostreams/operations.hpp&gt;</CODE></A></DT>
  64 </DL>
  65
  66 <A NAME="reference"></A>
  67 <H2>Reference</H2>
  68
  69 <A NAME="description"></A>
  70 <H4>Description</H4>
  71
  72 <P>Attemps to extract a character from a given instance of the template parameter <CODE>Source</CODE>, returning the extracted character or one of the special values <CODE>traits_type::eof</CODE> or <A HREF="../classes/char_traits.html#would_block"><CODE>traits_type::would_block</CODE></A>, where <CODE>traits_type</CODE> is an appropriate specialization of <A HREF="../classes/char_traits.html"><CODE>boost::iostreams::char_traits</CODE></A></P>
  73
  74 <A NAME="synopsis"></A>
  75 <H4>Synopsis</H4>
  76
  77 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
  78
  79     <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Source</A>&gt;
  80     <SPAN CLASS="keyword">typename</SPAN> <A CLASS='documented' HREF="../guide/traits.html#int_type_of_ref">int_type_of</A>&lt;Source&gt;::type
  81     <A CLASS="documented" HREF="#semantics">get</A>(<A CLASS="documented" HREF="#template_params">Source</A>&amp; <A CLASS="documented" HREF="#function_params">src</A>);
  82
  83 } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
  84
  85 <A NAME="template_params"></A>
  86 <H4>Template Parameters</H4>
  87
  88 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
  89 <TR>
  90     <TR>
  91         <TD VALIGN="top"><I>Source</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
  92         <TD>A model of <A HREF="../concepts/source.html">Source</A>.
  93     </TR>
  94 </TABLE>
  95
  96 <A NAME="function_params"></A>
  97 <H4>Function Parameters</H4>
  98
  99 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
 100 <TR>
 101     <TR>
 102         <TD VALIGN="top"><I>src</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 103         <TD>An instance of <CODE>Source</CODE></TD>
 104     </TR>
 105 </TABLE>
 106
 107 <A NAME="semantics"></A>
 108 <H4>Semantics</H4>
 109
 110 <PRE CLASS="broken_ie">    <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Source&gt;
 111     <SPAN CLASS="keyword">typename</SPAN> int_type_of&lt;Source&gt;::type
 112     get(Source&amp; src);</PRE>
 113
 114 <P>The semantics of <CODE>get</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>Source</CODE> as follows:</P>
 115
 116 <TABLE STYLE="margin:0,0,2em,2em" BORDER=1 CELLPADDING=4>
 117     <TR><TH><CODE>category_of&lt;Source&gt;::type</CODE></TH><TH>semantics</TH></TR>
 118     <TR>
 119         <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>direct_tag</CODE></A></TD>
 120         <TD>compile-time error</CODE></TD>
 121     </TR>
 122     <TR>
 123         <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>istream_tag</CODE></A></TD>
 124         <TD>returns <CODE>src.get()</CODE></TD>
 125     </TR>
 126     <TR>
 127         <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>streambuf_tag</CODE></A> but not to <A HREF="../guide/traits.html#category_tags"><CODE>istream_tag</CODE></A></TD>
 128         <TD>returns <CODE>src.sbumpc()</CODE></TD>
 129     </TR>
 130     <TR>
 131         <TD VALIGN="top">otherwise</TD>
 132         <TD>
 133             attempts to extract a single character using <CODE>src.read()</CODE>, returning the extracted character if successful and one of the special values <CODE>traits_type::eof</CODE> or <A HREF="../classes/char_traits.html#would_block"><CODE>traits_type::would_block</CODE></A> otherwise, where <CODE>traits_type</CODE> is <A HREF="../classes/char_traits.html"><CODE>boost::iostreams::char_traits&lt;Source&gt;</CODE></A>
 134         </TD>
 135     </TR>
 136 </TABLE>
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 142 <P CLASS="copyright">&copy; Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>&copy; Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a></P>
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 144     Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
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