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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"><ctype.h></SPAN> <SPAN CLASS="comment">// tolower</SPAN> | |
43 | <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/concepts.hpp"><SPAN CLASS="literal"><boost/iostreams/concepts.hpp></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"><boost/iostreams/operations.hpp></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><<SPAN CLASS="keyword">typename</SPAN> Source> | |
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><boost/iostreams/operations.hpp></CODE></A></DT> | |
67 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/read.hpp"><CODE><boost/iostreams/read.hpp></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><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>> | |
86 | std::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><T>::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><<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>> | |
91 | std::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><T>::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 — Device Types</H4> | |
138 | ||
139 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T> | |
140 | std::streamsize read( T& t, | |
141 | <SPAN CLASS="keyword">typename</SPAN> char_type_of<T>::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<T>::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 — Filter Types</H4> | |
168 | ||
169 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T> | |
170 | std::streamsize read( T& t, | |
171 | Source& src, | |
172 | <SPAN CLASS="keyword">typename</SPAN> char_type_of<T>::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<T>::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<Source></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">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© 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 | ||
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