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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2<HTML>
3<HEAD>
4    <TITLE>Function Template write</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>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& 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& snk)
59        {
60            std::reverse(data.begin(), data.end());
61            boost::iostreams::write(&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;     
89std::streamsize
90<A CLASS="documented" HREF="#write_device">write</A>( T& <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;
95std::streamsize
96<A CLASS="documented" HREF="#write_filter">write</A>( T& <A CLASS="documented" HREF="#function_params">t</A>,
97       Sink& <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;     
145std::streamsize
146write( T& 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;
172std::streamsize
173write( T& t,
174       Sink& 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>
191
192<!-- Begin Footer -->
193
194<HR>
195<P CLASS="copyright">Revised
196<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
19720 May, 2004
198<!--webbot bot="Timestamp" endspan i-checksum="38504" -->
199</P>
200
201<P CLASS="copyright">&copy; Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P>
202<P CLASS="copyright"> 
203    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>)
204</P>
205
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