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193 lines
9.3 KiB
HTML
Executable File
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML>
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<HEAD>
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<TITLE>Function Template read</TITLE>
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<LINK REL='stylesheet' HREF='../../../../boost.css'>
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<LINK REL='stylesheet' HREF='../theme/iostreams.css'>
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</HEAD>
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<BODY>
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<!-- Begin Banner -->
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<H1 CLASS='title'>Function Template <CODE>read</CODE></H1>
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<HR CLASS='banner'>
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<DL class='page-index'>
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<DT><A href='#overview'>Overview</A></DT>
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<DT><A href='#example'>Example</A></DT>
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<DT><A href='#headers'>Headers</A></DT>
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<DT><A href='#reference'>Reference</A></DT>
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</DL>
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<A NAME='overview'>
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<H2>Overview</H2>
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<P>
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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>.
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<UL>
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<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='../concepts.html#device_concepts'>Device</A> concepts.
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<LI>The second overload is primarily for internal use by the library.
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</UL>
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</P>
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<P>
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Although <CODE>read</CODE> is designed to be overloaded or specialized for new Filter and Device types, the default implementation should be suitable for most purposes.</P>
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</P>
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<A NAME='example'>
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<H2>Example</H2>
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<P>
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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>.
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</P>
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<PRE CLASS='broken_ie'> <SPAN CLASS='preprocessor'>#include</SPAN> <SPAN CLASS='literal'><ctype.h></SPAN> <SPAN CLASS='comment'>// tolower</SPAN>
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<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>
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<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>
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<SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> std;
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<SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> boost::io;
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<SPAN CLASS="keyword">struct</SPAN> tolower_filter : <SPAN CLASS="keyword">public</SPAN> multichar_input_filter {
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<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> Source>
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streamsize read(Source& src, <SPAN CLASS="keyword">char</SPAN>* s, streamsize n)
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{
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streamsize result = boost::iostreams::read(src, s, n);
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<SPAN CLASS="keyword">for</SPAN> (streamsize z = <SPAN CLASS='numeric_literal'>0</SPAN>; z < result; ++z)
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s[z] = tolower(s[z]);
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<SPAN CLASS="keyword">return</SPAN> result;
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}
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};</PRE>
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<A NAME='headers'>
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<H2>Headers</H2>
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<DL>
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<DT><A CLASS='header' HREF='../../../../boost/iostreams/operations.hpp'><CODE><boost/iostreams/operations.hpp></CODE></A></DT>
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</DL>
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<A NAME='reference'>
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<H2>Reference</H2>
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<A NAME='description'>
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<H4>Description</H4>
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Reads a sequence of characters from a given instance of the template parameter <CODE>T</CODE>, returning the number of characters read.
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<A NAME='synopsis'>
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<H4>Synopsis</H4>
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<PRE CLASS='broken_ie'><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
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<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>>
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std::streamsize <A CLASS="documented" HREF="#read_device">read</A>( T& <A CLASS="documented" HREF="#function_params">t</A>, <SPAN CLASS="keyword">typename</SPAN> <A CLASS='documented' HREF='../traits.html#char_type_ref'>io_char</A><T>::type* <A CLASS="documented" HREF="#function_params">s</A>, std::streamsize <A CLASS="documented" HREF="#function_params">n</A> );
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<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>>
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std::streamsize <A CLASS="documented" HREF="#read_filter">read</A>( T& <A CLASS="documented" HREF="#function_params">t</A>, Source& <A CLASS="documented" HREF="#function_params">src</A>, <SPAN CLASS="keyword">typename</SPAN> <A CLASS='documented' HREF='../traits.html#char_type_ref'>io_char</A><T>::type* <A CLASS="documented" HREF="#function_params">s</A>, std::streamsize <A CLASS="documented" HREF="#function_params">n</A> );
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} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>
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<A NAME='template_params'></A>
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<H4>Template Parameters</H4>
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<TABLE STYLE='margin-left:2em' BORDER=0 CELLPADDING=2>
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<TR>
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<TR>
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<TD VALIGN='top'><I>T</I></TD><TD WIDTH='2em' VALIGN='top'>-</TD>
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<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>.
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</TR>
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<TR>
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<TD VALIGN='top'><I>Source</I></TD><TD WIDTH='2em' VALIGN='top'>-</TD>
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<TD>A model of <A HREF='../concepts/source.html'>Source</A> with the same <A HREF='../traits.html#char_type'>character type</A> as <CODE>T</CODE> whose <A HREF='../modes.html'>i/o mode</A> refines that of <CODE>T</CODE>. <CODE>Source</CODE> must also model <A HREF='../concepts/peekable.html'>Peekable</A>.
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</TR>
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</TABLE>
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<A NAME='function_params'></A>
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<H4>Function Parameters</H4>
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<TABLE STYLE='margin-left:2em' BORDER=0 CELLPADDING=2>
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<TR>
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<TR>
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<TD VALIGN='top'><I>t</I></TD><TD WIDTH='2em' VALIGN='top'>-</TD>
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<TD>An instance of the Filter or Device type <CODE>T</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN='top'><I>s</I></TD><TD WIDTH='2em' VALIGN='top'>-</TD>
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<TD>The buffer into which characters should be read</TD>
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</TR>
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<TR>
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<TD VALIGN='top'><I>n</I></TD><TD WIDTH='2em' VALIGN='top'>-</TD>
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<TD>The maximum number of characters to read</TD>
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</TR>
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<TR>
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<TD VALIGN='top'><I>src</I></TD><TD WIDTH='2em' VALIGN='top'>-</TD>
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<TD>An instance of <CODE>Source</CODE>
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</TR>
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</TABLE>
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<A NAME='read_device'></A>
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<H4>Semantics — Device Types</H4>
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<PRE CLASS='broken_ie'><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T>
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std::streamsize read( T& t, <SPAN CLASS="keyword">typename</SPAN> io_char<T>::type* s, std::streamsize n );</PRE>
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<P>The semantics of <CODE>read</CODE> depends on the <A HREF="../traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
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<TABLE STYLE='margin-left:2em' BORDER=1 CELLPADDING=4>
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<TR><TH><CODE>io_category<T>::type</CODE></TH><TH>semantics</TH></TR>
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<TR>
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<TD VALIGN='top'>convertible to <A HREF='../traits.html#category_tags'><CODE>istream_tag</CODE></A></TD>
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<TD>invokes <CODE>t.read(s, n)</CODE> and returns <CODE>t.gcount()</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN='top'>convertible to <A HREF='../traits.html#category_tags'><CODE>streambuf_tag</CODE></A> but not to <A HREF='../traits.html#category_tags'><CODE>istream_tag</CODE></A></TD>
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<TD>returns <CODE>t.sgetn(s, n)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN='top'><I>not</I> convertible to <A HREF='../traits.html#category_tags'><CODE>direct_tag</CODE></A></TD>
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<TD>returns <CODE>t.read(s, n)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN='top'>otherwise</TD>
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<TD>compile-time error</CODE></TD>
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</TR>
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</TABLE>
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<A NAME='read_filter'></A>
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<H4>Semantics — Filter Types</H4>
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<PRE CLASS='broken_ie'><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T>
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std::streamsize read( T& t, Source& src, <SPAN CLASS="keyword">typename</SPAN> io_char<T>::type* s, std::streamsize n );</PRE>
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<P>The semantics of <CODE>read</CODE> depends on the <A HREF="../traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
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<TABLE STYLE='margin-bottom:2em;margin-left:2em' BORDER=1 CELLPADDING=4>
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<TR><TH><CODE>io_category<T>::type</CODE></TH><TH>semantics</TH></TR>
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<TR>
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<TD VALIGN='top'>convertible to <A HREF='../traits.html#category_tags'><CODE>multichar_tag</CODE></A></TD>
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<TD>returns <CODE>t.read(src, s, n)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN='top'>otherwise</TD>
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<TD>reads up to <CODE>n</CODE> characters into <CODE>s</CODE> by invoking <CODE>t.get(src)</CODE> repeatedly, halting if an end-of-stream indicator is returned; returns the number of characters successfully read</TD>
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</TR>
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</TABLE>
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<!-- Begin Footer -->
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<HR>
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<P CLASS='copyright'>Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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20 May, 2004
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<!--webbot bot="Timestamp" endspan i-checksum="38504" -->
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</P>
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<P CLASS='copyright'>© Copyright Jonathan Turkanis, 2004</P>
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<P CLASS='copyright'>
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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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</P>
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