Planet
navi homePPSaboutscreenshotsdownloaddevelopmentforum

source: downloads/boost_1_34_1/libs/iostreams/doc/functions/read.html @ 29

Last change on this file since 29 was 29, checked in by landauf, 16 years ago

updated boost from 1_33_1 to 1_34_1
File size: 10.3 KB
Line 
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& 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;     
86std::streamsize <A CLASS="documented" HREF="#read_device">read</A>( T& <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;
91std::streamsize <A CLASS="documented" HREF="#read_filter">read</A>( T& <A CLASS="documented" HREF="#function_params">t</A>,
92                      Source& <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;     
140std::streamsize read( T& 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;
170std::streamsize read( T& t,
171                      Source& 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<P CLASS="copyright">Revised
195<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
19620 May, 2004
197<!--webbot bot="Timestamp" endspan i-checksum="38504" -->
198</P>
199
200<P CLASS="copyright">&copy; Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P>
201<P CLASS="copyright"> 
202    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>)
203</P>
204
205<!-- End Footer -->
206
207</BODY>
Note: See TracBrowser for help on using the repository browser.