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4     <TITLE>Function Template write</TITLE>
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10 <!-- Begin Banner -->
11 
12     <H1 CLASS="title">Function Template <CODE>write</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>write</CODE> provide a uniform interface for writing a sequence of characters to a <A HREF="../concepts/source.html">Sink</A> or <A HREF="../concepts/output_filter.html">OutputFilter</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>write</CODE> in the definition of an <A HREF="../concepts/output_filter.html">OutputFilter</A> which reverses its controlled sequence.
40 </P>
41 
42 <PRE CLASS="broken_ie">    <SPAN CLASS="preprocessor">#include</SPAN> <SPAN CLASS="literal">&lt;algorithm&gt;</SPAN>                      <SPAN CLASS="comment">// reverse</SPAN>
43     <SPAN CLASS="preprocessor">#include</SPAN> <SPAN CLASS="literal">&lt;vector&gt;</SPAN>
44     <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">// output_filter</SPAN>
45     <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">// write</SPAN>
46 
47     <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> std;
48     <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> boost::io;
49 
50     <SPAN CLASS="keyword">struct</SPAN> reversing_filter : <SPAN CLASS="keyword">public</SPAN> multichar_output_filter {
51         <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Sink&gt;
52         std::streamsize write(Sink&amp; snk, <SPAN CLASS="keyword">const</SPAN> <SPAN CLASS="keyword">char</SPAN>* s, streamsize n)
53         {
54             data.insert(data.end(), s, s + n);
55             <SPAN CLASS="keyword">return</SPAN> n;
56         }
57         <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> Sink&gt;
58         <SPAN CLASS="keyword">void</SPAN> close(Sink&amp; snk)
59         {
60             std::reverse(data.begin(), data.end());
61             boost::iostreams::write(&amp;data[0], (streamsize) data.size());
62             data.clear();
63         }
64         std::vector&lt;<SPAN CLASS="keyword">char</SPAN>&gt; data;
65     };</PRE>
66 
67 <A NAME="headers"></A>
68 <H2>Headers</H2>
69 
70 <DL>
71   <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE>&lt;boost/iostreams/operations.hpp&gt;</CODE></A></DT>
72   <DT><A CLASS="header" HREF="../../../../boost/iostreams/write.hpp"><CODE>&lt;boost/iostreams/write.hpp&gt;</CODE></A></DT>
73 </DL>
74 
75 <A NAME="reference"></A>
76 <H2>Reference</H2>
77 
78 <A NAME="description"></A>
79 <H4>Description</H4>
80 
81 <P>Attempts to write a sequence of characters to a given instance of the template parameter <CODE>T</CODE>, returning the number of characters written.</P>
82 
83 <A NAME="synopsis"></A>
84 <H4>Synopsis</H4>
85 
86 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
87 
88 <SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>&gt;
89 std::streamsize
90 <A CLASS="documented" HREF="#write_device">write</A>( T&amp; <A CLASS="documented" HREF="#function_params">t</A>,
91        <SPAN CLASS="keyword">const</SPAN> <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>,
92        std::streamsize <A CLASS="documented" HREF="#function_params">n</A> );
93 
94 <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">Sink</A>&gt;
95 std::streamsize
96 <A CLASS="documented" HREF="#write_filter">write</A>( T&amp; <A CLASS="documented" HREF="#function_params">t</A>,
97        Sink&amp; <A CLASS="documented" HREF="#function_params">snk</A>,
98        <SPAN CLASS="keyword">const</SPAN> <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>,
99        std::streamsize <A CLASS="documented" HREF="#function_params">n</A> );
100 
101 } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
102 
103 <A NAME="template_params"></A>
104 <H4>Template Parameters</H4>
105 
106 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
107 <TR>
108     <TR>
109         <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
110         <TD>For the first overload, a model of <A HREF="../concepts/sink.html">Sink</A>. For the second overload, a model of <A HREF="../concepts/output_filter.html">OutputFilter</A>.
111     </TR>
112     <TR>
113         <TD VALIGN="top"><I>Sink</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
114         <TD>A model of <A HREF="../concepts/sink.html">Sink</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>.
115     </TR>
116 </TABLE>
117 
118 <A NAME="function_params"></A>
119 <H4>Function Parameters</H4>
120 
121 <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
122 <TR>
123     <TR>
124         <TD VALIGN="top"><I>t</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
125         <TD>An instance of T</CODE></TD>
126     </TR>
127     <TR>
128         <TD VALIGN="top"><I>s</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
129         <TD>A buffer containing characters to write</TD>
130     </TR>
131     <TR>
132         <TD VALIGN="top"><I>n</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
133         <TD>The number of characters to write</TD>
134     </TR>
135     <TR>
136         <TD VALIGN="top"><I>snk</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
137         <TD>An instance of <CODE>Sink</CODE>.
138     </TR>
139 </TABLE>
140 
141 <A NAME="write_device"></A>
142 <H4>Semantics &#8212; Device Types</H4>
143 
144 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> T&gt;
145 std::streamsize
146 write( T&amp; t,
147        <SPAN CLASS="keyword">const</SPAN> <SPAN CLASS="keyword">typename</SPAN> char_type_of&lt;T&gt;::type* s,
148        std::streamsize n );</PRE>
149 
150 <P>The semantics of <CODE>write</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
151 
152 <TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
153     <TR><TH><CODE>category_of&lt;T&gt;::type</CODE></TH><TH>semantics</TH></TR>
154     <TR>
155         <TD VALIGN="top">convertible to <CODE>ostream_tag</CODE></TD>
156         <TD>returns <CODE>t.rdbuf()->sputn(s, n)</CODE></TD>
157     </TR>
158     <TR>
159         <TD VALIGN="top">convertible to <CODE>streambuf_tag</CODE> but not to <CODE>ostream_tag</CODE></TD>
160         <TD>returns <CODE>t.sputn(s, n)</CODE></TD>
161     </TR>
162     <TR>
163         <TD VALIGN="top">otherwise</TD>
164         <TD>returns <CODE>t.write(s, n)</CODE></TD>
165     </TR>
166 </TABLE>
167 
168 <A NAME="write_filter"></A>
169 <H4>Semantics &#8212; Filter Types</H4>
170 
171 <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> T, <SPAN CLASS="keyword">typename</SPAN> Sink&gt;
172 std::streamsize
173 write( T&amp; t,
174        Sink&amp; snk,
175        <SPAN CLASS="keyword">const</SPAN> <SPAN CLASS="keyword">typename</SPAN> char_type_of&lt;T&gt;::type* s,
176        std::streamsize n );</PRE>
177 
178 <P>The semantics of <CODE>write</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
179 
180 <TABLE STYLE="margin:0,0,2em,2em" BORDER=1 CELLPADDING=4>
181     <TR><TH><CODE>category_of&lt;T&gt;::type</CODE></TH><TH>semantics</TH></TR>
182     <TR>
183         <TD VALIGN="top">convertible to <CODE>multichar_tag</CODE></TD>
184         <TD>returns <CODE>t.write(snk, s, n)</CODE></TD>
185     </TR>
186     <TR>
187         <TD VALIGN="top"><I>otherwise</I></TD>
188         <TD>Attempts to write <CODE>n</CODE> characters from <CODE>s</CODE> by invoking <CODE>t.put(snk, s[m])</CODE> for each value <CODE>m</CODE> in the interval <CODE>[0, n)</CODE>, halting if <CODE>put</CODE> returns <CODE>false</CODE>. Returns the number of characters written.</TD>
189     </TR>
190 </TABLE>
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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="https://www.boost.org/users/people/jonathan_turkanis.html" 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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