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

   1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
   2 <HTML>
   3 <HEAD>
   4     <TITLE>Function Template read</TITLE>
   5     <LINK REL="stylesheet" HREF="../../../../boost.css">
   6     <LINK REL="stylesheet" HREF="../theme/iostreams.css">
   7 </HEAD>
   8 <BODY>
   9
  10 <!-- Begin Banner -->
  11
  12     <H1 CLASS="title">Function Template <CODE>read</CODE></H1>
  13     <HR CLASS="banner">
  14
  15 <!-- End Banner -->
  16
  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 two overloads of the function template <CODE>read</CODE> provide a uniform interface for reading a sequence of characters from a <A HREF="../concepts/source.html">Source</A> or <A HREF="../concepts/input_filter.html">InputFilter</A>.
  29     <UL>
  30         <LI>The first overload can be used directly in the definitions of new Filter types (<I>see</I> <A HREF="#example">Example</A>), and figures in the specification of the <A HREF="../guide/concepts.html#device_concepts">Device</A> concepts.
  31         <LI>The second overload is primarily for internal use by the library.
  32     </UL>
  33 </P>
  34
  35 <A NAME="example"></A>
  36 <H2>Example</H2>
  37
  38 <P>
  39     The following code illustrates the use of the function <CODE>read</CODE> in the definition of a <A HREF="../concepts/multi_character.html">Multi-Character</A> <A HREF="../concepts/input_filter.html">InputFilter</A>.
  40 </P>
  41
  42 <PRE CLASS="broken_ie">    <SPAN CLASS="preprocessor">#include</SPAN> <SPAN CLASS="literal">&lt;ctype.h&gt;</SPAN>                        <SPAN CLASS="comment">// tolower</SPAN>
  43     <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">// multichar_input_filter</SPAN>
  44     <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">// read</SPAN>
  45
  46     <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> std;
  47     <SPAN CLASS="keyword">namespace</SPAN> io = boost::iostreams;
  48
  49     <SPAN CLASS="keyword">struct</SPAN> tolower_filter : <SPAN CLASS="keyword">public</SPAN> io::multichar_input_filter {
  50         <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Source&gt;
  51         streamsize read(Source&amp; src, <SPAN CLASS="keyword">char</SPAN>* s, streamsize n)
  52         {
  53             streamsize result;
  54             <SPAN CLASS="keyword">if</SPAN> ((result = io::read(src, s, n)) == <SPAN CLASS='numeric_literal'>-1</SPAN>)
  55                 <SPAN CLASS="keyword">return</SPAN> <SPAN CLASS='numeric_literal'>-1</SPAN>; <SPAN CLASS='comment'>// EOF</SPAN>
  56             <SPAN CLASS="keyword">for</SPAN> (streamsize z = <SPAN CLASS="numeric_literal">0</SPAN>; z < result; ++z)
  57                 s[z] = tolower((<SPAN CLASS="keyword">unsigned</SPAN> <SPAN CLASS="keyword">char</SPAN>) s[z]);
  58             <SPAN CLASS="keyword">return</SPAN> result;
  59         }
  60     };</PRE>
  61
  62 <A NAME="headers"></A>
  63 <H2>Headers</H2>
  64
  65 <DL>
  66   <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE>&lt;boost/iostreams/operations.hpp&gt;</CODE></A></DT>
  67   <DT><A CLASS="header" HREF="../../../../boost/iostreams/read.hpp"><CODE>&lt;boost/iostreams/read.hpp&gt;</CODE></A></DT>
  68 </DL>
  69
  70 <A NAME="reference"></A>
  71 <H2>Reference</H2>
  72
  73 <A NAME="description"></A>
  74 <H4>Description</H4>
  75
  76 <P>
  77     Reads a sequence of characters from a given instance of the template parameter <CODE>T</CODE>, returning the number of characters read, or <CODE>-1</CODE> to indicate end-of-sequence.
  78 </P>
  79
  80 <A NAME="synopsis"></A>
  81 <H4>Synopsis</H4>
  82
  83 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
  84
  85 <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>&gt;
  86 std::streamsize <A CLASS="documented" HREF="#read_device">read</A>( T&amp; <A CLASS="documented" HREF="#function_params">t</A>,
  87                       <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="../guide/traits.html#char_type_of_ref">char_type_of</A>&lt;T&gt;::type* <A CLASS="documented" HREF="#function_params">s</A>,
  88                       std::streamsize <A CLASS="documented" HREF="#function_params">n</A> );
  89
  90 <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>, <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Source</A>&gt;
  91 std::streamsize <A CLASS="documented" HREF="#read_filter">read</A>( T&amp; <A CLASS="documented" HREF="#function_params">t</A>,
  92                       Source&amp; <A CLASS="documented" HREF="#function_params">src</A>,
  93                       <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="../guide/traits.html#char_type_of_ref">char_type_of</A>&lt;T&gt;::type* <A CLASS="documented" HREF="#function_params">s</A>,
  94                       std::streamsize <A CLASS="documented" HREF="#function_params">n</A> );
  95
  96 } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
  97
  98 <A NAME="template_params"></A>
  99 <H4>Template Parameters</H4>
 100
 101 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
 102 <TR>
 103     <TR>
 104         <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 105         <TD>For the first overload, a model of <A HREF="../concepts/source.html">Source</A> or a standard input stream or stream buffer type. For the second overload, a model of <A HREF="../concepts/input_filter.html">InputFilter</A>.
 106     </TR>
 107     <TR>
 108         <TD VALIGN="top"><I>Source</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 109         <TD>An <A HREF="../concepts/direct.html">indirect</A> model of <A HREF="../concepts/source.html">Source</A> with the same <A HREF="../guide/traits.html#char_type">character type</A> as <CODE>T</CODE> whose <A HREF="../guide/modes.html">mode</A> refines that of <CODE>T</CODE>. <CODE>Source</CODE> must also model <A HREF="../concepts/peekable.html">Peekable</A>.
 110     </TR>
 111 </TABLE>
 112
 113 <A NAME="function_params"></A>
 114 <H4>Function Parameters</H4>
 115
 116 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
 117 <TR>
 118     <TR>
 119         <TD VALIGN="top"><I>t</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 120         <TD>An instance of the Filter or Device type <CODE>T</CODE></TD>
 121     </TR>
 122     <TR>
 123         <TD VALIGN="top"><I>s</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 124         <TD>The buffer into which characters should be read</TD>
 125     </TR>
 126     <TR>
 127         <TD VALIGN="top"><I>n</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 128         <TD>The maximum number of characters to read</TD>
 129     </TR>
 130     <TR>
 131         <TD VALIGN="top"><I>src</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 132         <TD>An instance of <CODE>Source</CODE>
 133     </TR>
 134 </TABLE>
 135
 136 <A NAME="read_device"></A>
 137 <H4>Semantics &#8212; Device Types</H4>
 138
 139 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> T&gt;
 140 std::streamsize read( T&amp; t,
 141                       <SPAN CLASS="keyword">typename</SPAN> char_type_of&lt;T&gt;::type* s,
 142                       std::streamsize n );</PRE>
 143
 144 <P>The semantics of <CODE>read</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
 145
 146 <TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
 147     <TR><TH><CODE>category_of&lt;T&gt;::type</CODE></TH><TH>semantics</TH></TR>
 148     <TR>
 149         <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>istream_tag</CODE></A></TD>
 150         <TD>invokes <CODE>t.read(s, n)</CODE> and returns <CODE>t.gcount()</CODE></TD>
 151     </TR>
 152     <TR>
 153         <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>
 154         <TD>returns <CODE>t.sgetn(s, n)</CODE></TD>
 155     </TR>
 156     <TR>
 157         <TD VALIGN="top"><I>not</I> convertible to <A HREF="../guide/traits.html#category_tags"><CODE>direct_tag</CODE></A></TD>
 158         <TD>returns <CODE>t.read(s, n)</CODE></TD>
 159     </TR>
 160     <TR>
 161         <TD VALIGN="top">otherwise</TD>
 162         <TD>compile-time error</CODE></TD>
 163     </TR>
 164 </TABLE>
 165
 166 <A NAME="read_filter"></A>
 167 <H4>Semantics &#8212; Filter Types</H4>
 168
 169 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> T&gt;
 170 std::streamsize read( T&amp; t,
 171                       Source&amp; src,
 172                       <SPAN CLASS="keyword">typename</SPAN> char_type_of&lt;T&gt;::type* s,
 173                       std::streamsize n );</PRE>
 174
 175 <P>The semantics of <CODE>read</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
 176
 177 <TABLE STYLE="margin-bottom:2em;margin-left:2em" BORDER=1 CELLPADDING=4>
 178     <TR><TH><CODE>category_of&lt;T&gt;::type</CODE></TH><TH>semantics</TH></TR>
 179     <TR>
 180         <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>multichar_tag</CODE></A></TD>
 181         <TD>returns <CODE>t.read(src, s, n)</CODE></TD>
 182     </TR>
 183     <TR>
 184         <TD VALIGN="top">otherwise</TD>
 185         <TD>
 186             reads up to <CODE>n</CODE> characters into <CODE>s</CODE> by invoking <CODE>t.get(src)</CODE> repeatedly, halting if <CODE>traits_typre::eof</CODE> or <A HREF="../classes/char_traits.html#would_block"><CODE>traits_type::would_block</CODE></A> is returned, where <CODE>traits_type</CODE> is <A HREF="../classes/char_traits.html"><CODE>boost::iostreams::char_traits&lt;Source&gt;</CODE></A></A>. Returns the number of characters read, or <CODE>-1</CODE> to indicate end-of-sequence.
 187         </TD>
 188     </TR>
 189 </TABLE>
 190
 191 <!-- Begin Footer -->
 192
 193 <HR>
 194
 195 <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>
 196 <P CLASS="copyright">
 197     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>)
 198 </P>
 199
 200 <!-- End Footer -->
 201
 202 </BODY>