ceph/src/boost/libs/iostreams/doc/classes/code_converter.html

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   4     <TITLE>Class Template code_converter</TITLE>
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  12     <H1 CLASS="title">Class Template <CODE>code_converter</CODE></H1>
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  17 <DL class="page-index">
  18   <DT><A href="#description">Description</A></DT>
  19   <DT><A href="#headers">Headers</A></DT>
  20   <DT><A href="#reference">Reference</A></DT>
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  24
  25 <A NAME="description"></A>
  26 <H2>Description</H2>
  27
  28 <P>
  29     The class templates <CODE>code_converter</CODE> is a <SPAN CLASS="term">Device adapter</SPAN> which takes a Device with a narrow <A HREF="../guide/traits.html#char_type">character type</A> \97 typically <CODE>char</CODE> \97 and produces a Device with wide character type \97 typically <CODE>wchar_t</CODE> \97 by introducing a layer of <A HREF="../guide/code_conversion.html">code conversion</A>. The code conversion is performed using a <CODE>std::codecvt</CODE> facet which can either be specified as a template parameter or be fetched from a <CODE>std::locale</CODE> provided at runtime.
  30 </P>
  31 <P>
  32     For example, we can define a wide-character Device for reading from a memory-mapped file as follows:
  33     <PRE CLASS="broken_ie">    <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/device/mapped_file.hpp"><SPAN CLASS="literal">&lt;boost/iostreams/maped_file.hpp&gt;</SPAN></A>
  34
  35     <SPAN CLASS="keyword">typedef</SPAN> code_converter&lt;mapped_file_source&gt; my_source;</PRE>
  36
  37     Similarly, we can define a wide-character Device which writes multibyte characters to an in-memory character sequence as follows:
  38
  39     <PRE CLASS="broken_ie">    <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/device/array.hpp"><SPAN CLASS="literal">&lt;boost/iostreams/device/array.hpp&gt;</SPAN></A>
  40
  41     <SPAN CLASS="keyword">typedef</SPAN> code_converter&lt;array_sink&gt; my_sink;</PRE>
  42 </P>
  43 <P>
  44     The <A HREF="../guide/modes.html">mode</A> of a specialization of <CODE>code_converter</CODE> is determined as follows. If a narrow character Device is read-only, the resulting specialization of <CODE>code_converter</CODE> has mode <A HREF="../guide/modes.html#input">input</A>. If a narrow character Device is write-only, the resulting specialization of <CODE>code_converter</CODE> has mode <A HREF="../guide/modes.html#output">output</A>. If a narrow character Device performs input and output using two distinct sequences (<I>see</I> <A HREF="../guide/modes.html">Modes</A>), the resulting specialization of <CODE>code_converter</CODE> has mode <A HREF="../guide/modes.html#bidirectional">bidirectional</A>. Otherwise, attempting to spcialize <CODE>code_converter</CODE> results in a compile-time error.
  45 </P>
  46
  47 <A NAME="headers"></A>
  48 <H2>Headers</H2>
  49
  50 <DL class="page-index">
  51   <DT><A CLASS="header" HREF="../../../../boost/iostreams/code_converter.hpp"><CODE>&lt;boost/iostreams/code_converter.hpp&gt;</CODE></A></DT>
  52 </DL>
  53
  54 <A NAME="reference"></A>
  55 <H2>Reference</H2>
  56
  57 <H4>Synopsis</H4>
  58
  59 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
  60
  61 <SPAN CLASS="keyword">template</SPAN>&lt; <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Device</A>,
  62           <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Codecvt</A> = <SPAN CLASS='omitted'>default_value</SPAN>
  63           <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Alloc</A> = std::allocator&lt;<CODE>char</CODE>&gt; &gt;
  64 <SPAN CLASS="keyword">class</SPAN> <A CLASS="documented" HREF="#template_params">code_converter</A> {
  65 <SPAN CLASS="keyword">public</SPAN>:
  66     <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="keyword">typename</SPAN> Codecvt::intern_type  char_type;
  67     <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">implementation-defined</SPAN>         category;
  68     <A CLASS="documented" HREF="#constructors">code_converter</A>();
  69     <A CLASS="documented" HREF="#constructors">code_converter</A>( <SPAN CLASS="keyword">const</SPAN> Device&amp; dev,
  70                     int buffer_size = <SPAN CLASS="omitted">default_value</SPAN> );
  71     <A CLASS="documented" HREF="code_converter.html#constructors">code_converter</A>( <SPAN CLASS="omitted">device-constructor-args...</SPAN>,
  72                     int buffer_size = <SPAN CLASS="omitted">default_value</SPAN> );
  73     <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="code_converter.html#open">open</A>( <SPAN CLASS="keyword">const</SPAN> Device&amp; dev,
  74                int buffer_size = <SPAN CLASS="omitted">default_value</SPAN> );
  75     <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="code_converter.html#open">open</A>( <SPAN CLASS="omitted">device-constructor-args...</SPAN>,
  76                int buffer_size = <SPAN CLASS="omitted">default_value</SPAN> );
  77     <SPAN CLASS="keyword">bool</SPAN> <A CLASS="documented" HREF="#is_open">is_open</A>() <SPAN CLASS="keyword">const</SPAN>;
  78     <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#close">close</A>();
  79     std::locale <A CLASS="documented" HREF="#imbue">imbue</A>(<SPAN CLASS="keyword">const</SPAN> std::locale&amp; loc);
  80     Device&amp; <A CLASS="documented" HREF="#operator_star">operator*</A>();
  81     Device* <A CLASS="documented" HREF="#operator_arrow">operator-&gt;</A>();
  82 };
  83
  84 } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
  85
  86 <A NAME="template_params"></A>
  87 <H4>Template parameters</H4>
  88
  89 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
  90 <TR>
  91     <TR>
  92         <TD VALIGN="top"><I>Device</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
  93         <TD>A model of one of the <A HREF="../guide/concepts.html#device_concepts">Device</A> concepts; typically has <A HREF="../guide/traits.html#char_type">character type</A> <CODE>char</CODE>.</TD>
  94     </TR>
  95     <TR>
  96         <TD VALIGN="top"><I>Codecvt</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
  97         <TD>
  98             A standard library codecvt facet, which must be default constructible. If this parameter is not specified,
  99             an instance of <CODE>std::codecvt&lt;wchar_t, char, std::mbstate_t&gt;</CODE> will be fetched from the global
 100             local when a <CODE>code_converter</CODE> is constructed or opened.
 101         </TD>
 102     </TR>
 103     <TR>
 104         <TD VALIGN="top"><I>Alloc</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
 105         <TD>A standard library allocator type (<A CLASS="bib_ref" HREF="../bibliography.html#iso">[ISO]</A>, 20.1.5), used to allocate character buffers</TD>
 106     </TR>
 107 </TABLE>
 108
 109 <A NAME="constructors"></A>
 110 <H4><CODE>code_converter::code_converter</CODE></H4>
 111
 112 <PRE CLASS="broken_ie">    code_converter();
 113     code_converter( <SPAN CLASS="keyword">const</SPAN> Device&amp; dev,
 114                     int buffer_size );
 115     code_converter( <SPAN CLASS="omitted">device-constructor-args...</SPAN>,
 116                     int buffer_size );</PRE>
 117
 118 <P>
 119     The first member constructs a <CODE>code_converter</CODE> with no associated instance of the Device type <CODE>Device</CODE>. Before the instance can be used for i/o, the member function <CODE>open()</CODE> must be invoked.
 120 </P>
 121
 122 <P>
 123     The second member constructs a <CODE>code_converter</CODE> based on the given instance of <CODE>Device</CODE>. The second parameter determines the size of the buffers or buffers used for code conversion. If a <CODE>std::codecvt</CODE> was specified as a template parameter, an instance of it will be default constructed. Otherwise, a copy of the global <CODE>locale</CODE> will be made, and an instance of <CODE>std::codecvt&lt;wchar_t, char, std::mbstate_t&gt;</CODE> will be fetched from it.
 124 </P>
 125
 126 <P>
 127     The third member constructs a <CODE>code_converter</CODE> based on the given instance of <CODE>Device</CODE> constructed with the forwarded arguments. Take care as the <CODE>buffer_size</CODE> can be confused for a constructor argument if it isn't an <CODE>int</CODE>.<br>
 128 </P>
 129
 130 <A NAME="imbue"></A>
 131 <H4><CODE>code_converter::imbue</CODE></H4>
 132
 133 <PRE CLASS="broken_ie">    std::locale imbue(<SPAN CLASS="keyword">const</SPAN> std::locale&amp; loc);</PRE>
 134
 135 <P>
 136     Used to specify a locale from which a <CODE>std::codecvt</CODE> facet will be fetched to perform code conversion. The effect of invoking imbue while code conversion is in progress is undefined.
 137 </P>
 138
 139 <P>
 140     This function is a no-op if a <CODE>std::codecvt</CODE> facet was specified as a template parameter.
 141 </P>
 142
 143 <A NAME="open"></A>
 144 <H4><CODE>code_converter::open</CODE></H4>
 145
 146 <PRE CLASS="broken_ie">     <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="keyword">const</SPAN> Device&amp; dev,
 147                 std::streamsize buffer_size = <SPAN CLASS="omitted">default_value</SPAN> );
 148      <SPAN CLASS="keyword">void</SPAN> open( <SPAN CLASS="omitted">device-constructor-args</SPAN>,
 149                 std::streamsize buffer_size = <SPAN CLASS="omitted">default_value</SPAN> );<br></PRE>
 150
 151 <P>
 152     Associates the given instance of <CODE>Device</CODE> with <CODE>this</CODE> instance of <CODE>code_converter</CODE>, if there is no such instance currently associated; otherwise, throws <CODE>std::ios_base::failure</CODE>. The second parameter determines the size of the buffer or buffers used for code conversion. If a <CODE>std::codecvt</CODE> was specified as a template parameter, an instance of it will be default constructed. Otherwise, a copy of the global <CODE>locale</CODE> will be made, and an instance of <CODE>std::codecvt&lt;wchar_t, char, std::mbstate_t&gt;</CODE> will be fetched from it.
 153 </P>
 154 <P>
 155     The second member constructs a <CODE>Device</CODE> with the forwarded arguments. Take care as the <CODE>buffer_size</CODE> can be confused for a constructor argument if it isn't an <CODE>int</CODE>.
 156 </P>
 157
 158 <A NAME="is_open"></A>
 159 <H4><CODE>code_converter::is_open</CODE></H4>
 160
 161 <PRE CLASS="broken_ie">    <SPAN CLASS="keyword">bool</SPAN> is_open() <SPAN CLASS="keyword">const</SPAN>;</PRE>
 162
 163 <P>Returns true if there is an instance of the Device type <CODE>Device</CODE> associated with <CODE>this</CODE> instance of <CODE>code_converter</CODE>.</P>
 164
 165 <A NAME="close"></A>
 166 <H4><CODE>code_converter::close</CODE></H4>
 167
 168 <PRE CLASS="broken_ie">    <SPAN CLASS="keyword">void</SPAN> close();</PRE>
 169
 170 <P>
 171     Disassociates from <CODE>this</CODE> instance of <CODE>code_converter</CODE> any instance of the Device type <CODE>Device</CODE> currently associated with it, calling cleanup functions as appropriate and destroying the associated instance of <CODE>Device</CODE>.
 172 </P>
 173
 174 <A NAME="operator_star"></A>
 175 <H4><CODE>code_converter::operator*</CODE></H4>
 176
 177 <PRE CLASS="broken_ie">    Device&amp; operator*();</PRE>
 178
 179 <P>
 180      Returns a reference to the instance of Device associated with this instance of <CODE>code_converter</CODE>, which must be <A HREF="#is_open">open</A>.
 181 </P>
 182
 183 <A NAME="operator_arrow"></A>
 184 <H4><CODE>code_converter::operator-></CODE></H4>
 185
 186 <PRE CLASS="broken_ie">    Device* operator->();</PRE>
 187
 188 <P>
 189     Returns a pointer to the instance of Device associated with this instance of <CODE>code_converter</CODE>, which must be <A HREF="#is_open">open</A>.
 190 </P>
 191
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 196 <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>
 197 <P CLASS="copyright">
 198     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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