1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4 <TITLE>Function Template get</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>get</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 function template <CODE>get</CODE> provides a uniform interface for reading a character from a <A HREF="../concepts/source.html">Source</A>, for use in the definitions of new <A HREF="../guide/concepts.html#filter_concepts">Filter</A> types (<I>see</I> <A HREF="#example">Example</A>). 29</P> 30 31<A NAME="example"></A> 32<H2>Example</H2> 33 34<P> 35 The following code illustrates the use of the function <CODE>get</CODE> in the definition of an <A HREF="../concepts/input_filter.html">InputFilter</A>. 36</P> 37 38<PRE CLASS="broken_ie"> <SPAN CLASS="preprocessor">#include</SPAN> <SPAN CLASS="literal"><ctype.h></SPAN> <SPAN CLASS="comment">// tolower</SPAN> 39 <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">// input_filter</SPAN> 40 <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">// get, EOF, WOULD_BLOCK</SPAN> 41 42 <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> std; 43 <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> boost::io; 44 45 <SPAN CLASS="keyword">struct</SPAN> tolower_filter : <SPAN CLASS="keyword">public</SPAN> input_filter { 46 <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> Source> 47 <SPAN CLASS="keyword">int</SPAN> get(Source& src) 48 { 49 <SPAN CLASS="keyword">int</SPAN> c; 50 <SPAN CLASS="keyword">return</SPAN> (c = boost::iostreams::get(src)) != <SPAN CLASS='numeric_literal'>EOF</SPAN> && 51 c != WOULD_BLOCK 52 ? 53 tolower((<SPAN CLASS="keyword">unsigned</SPAN> <SPAN CLASS="keyword">char</SPAN>) c) : 54 c; 55 } 56 };</PRE> 57 58<A NAME="headers"></A> 59<H2>Headers</H2> 60 61<DL> 62 <DT><A CLASS="header" HREF="../../../../boost/iostreams/get.hpp"><CODE><boost/iostreams/get.hpp></CODE></A></DT> 63 <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE><boost/iostreams/operations.hpp></CODE></A></DT> 64</DL> 65 66<A NAME="reference"></A> 67<H2>Reference</H2> 68 69<A NAME="description"></A> 70<H4>Description</H4> 71 72<P>Attemps to extract a character from a given instance of the template parameter <CODE>Source</CODE>, returning the extracted character or one of the special values <CODE>traits_type::eof</CODE> or <A HREF="../classes/char_traits.html#would_block"><CODE>traits_type::would_block</CODE></A>, where <CODE>traits_type</CODE> is an appropriate specialization of <A HREF="../classes/char_traits.html"><CODE>boost::iostreams::char_traits</CODE></A></P> 73 74<A NAME="synopsis"></A> 75<H4>Synopsis</H4> 76 77<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { 78 79 <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Source</A>> 80 <SPAN CLASS="keyword">typename</SPAN> <A CLASS='documented' HREF="../guide/traits.html#int_type_of_ref">int_type_of</A><Source>::type 81 <A CLASS="documented" HREF="#semantics">get</A>(<A CLASS="documented" HREF="#template_params">Source</A>& <A CLASS="documented" HREF="#function_params">src</A>); 82 83} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE> 84 85<A NAME="template_params"></A> 86<H4>Template Parameters</H4> 87 88<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> 89<TR> 90 <TR> 91 <TD VALIGN="top"><I>Source</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> 92 <TD>A model of <A HREF="../concepts/source.html">Source</A>. 93 </TR> 94</TABLE> 95 96<A NAME="function_params"></A> 97<H4>Function Parameters</H4> 98 99<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> 100<TR> 101 <TR> 102 <TD VALIGN="top"><I>src</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> 103 <TD>An instance of <CODE>Source</CODE></TD> 104 </TR> 105</TABLE> 106 107<A NAME="semantics"></A> 108<H4>Semantics</H4> 109 110<PRE CLASS="broken_ie"> <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> Source> 111 <SPAN CLASS="keyword">typename</SPAN> int_type_of<Source>::type 112 get(Source& src);</PRE> 113 114<P>The semantics of <CODE>get</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>Source</CODE> as follows:</P> 115 116<TABLE STYLE="margin:0,0,2em,2em" BORDER=1 CELLPADDING=4> 117 <TR><TH><CODE>category_of<Source>::type</CODE></TH><TH>semantics</TH></TR> 118 <TR> 119 <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>direct_tag</CODE></A></TD> 120 <TD>compile-time error</CODE></TD> 121 </TR> 122 <TR> 123 <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>istream_tag</CODE></A></TD> 124 <TD>returns <CODE>src.get()</CODE></TD> 125 </TR> 126 <TR> 127 <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> 128 <TD>returns <CODE>src.sbumpc()</CODE></TD> 129 </TR> 130 <TR> 131 <TD VALIGN="top">otherwise</TD> 132 <TD> 133 attempts to extract a single character using <CODE>src.read()</CODE>, returning the extracted character if successful and one of the special values <CODE>traits_type::eof</CODE> or <A HREF="../classes/char_traits.html#would_block"><CODE>traits_type::would_block</CODE></A> otherwise, where <CODE>traits_type</CODE> is <A HREF="../classes/char_traits.html"><CODE>boost::iostreams::char_traits<Source></CODE></A> 134 </TD> 135 </TR> 136</TABLE> 137 138<!-- Begin Footer --> 139 140<HR> 141 142<P CLASS="copyright">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© Copyright 2004-2007 <a href="https://www.boost.org/users/people/jonathan_turkanis.html" target="_top">Jonathan Turkanis</a></P> 143<P CLASS="copyright"> 144 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>) 145</P> 146 147<!-- End Footer --> 148 149</BODY> 150