1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4 <TITLE>Source</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">Source</H1> 13 <HR CLASS="banner"> 14 15<!-- End Banner --> 16 17<H2>Definition</H2> 18 19<P> 20 A Source is a <A HREF="device.html">Device</A> whose <A HREF="../guide/modes.html">mode</A> refines <A HREF="../guide/modes.html#input">input</A>. 21</P> 22 23<H2>Description</H2> 24 25<P>A Source provides read-access to a sequence of characters of a given type. In general, a Source may expose this sequence in two ways:</P> 26 27<OL> 28 <LI STYLE="list-style-type:lower-roman"> 29 by defining a member function <CODE>read</CODE>; or 30 </LI> 31 <LI STYLE="list-style-type:lower-roman"> 32 by defining a member function <CODE>input_sequence</CODE> returning a pair of pointers delimiting the sequence in its entirety. 33 </LI> 34</OL> 35 36<P>As a special case, Boost.Iostreams treats standard input streams as Sources. (For details, see <A HREF="../functions/read.html"><CODE>read</CODE></A>.)</P> 37 38<P>The mode of a Source is <A HREF="../guide/modes.html#input"><CODE>input</CODE></A> or one of its refinements.</P> 39 40<H2>Note</H2> 41 42<P>To be usable with the streams and stream buffers provided by the Boost Iostreams library, Sources must model <A HREF="blocking.html">Blocking</A>. 43 44<H2>Example</H2> 45 46<P> 47 A model of Source can be defined as follows: 48</P> 49 50<PRE CLASS="broken_ie"><SPAN CLASS="keyword">struct</SPAN> Source { 51 <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="keyword">char</SPAN> char_type; 52 <SPAN CLASS="keyword">typedef</SPAN> source_tag category; 53 std::streamsize read(<SPAN CLASS="keyword">char</SPAN>* s, std::streamsize n) 54 { 55 <SPAN CLASS="comment">// Read up to n characters from the input 56 // sequence into the buffer s, returning 57 // the number of characters read, or -1 58 // to indicate end-of-sequence.</SPAN> 59 } 60};</PRE> 61 62<P> 63 Here <CODE>source_tag</CODE> is a <A HREF="../guide/traits.html#category_tags">category tag</A> identifying the type as a model of Source. Typically a Source can be defined by deriving from the helper classes <A HREF="../classes/device.html#synopsis"><CODE>source</CODE></A> or <A HREF="../classes/device.html#synopsis"><CODE>wsource</CODE></A> and defining a member function <CODE>read</CODE>. 64 65<H2>Refinement of</H2> 66 67<P><A HREF="device.html">Device</A>.</P> 68 69<A NAME="types"></A> 70<H2>Associated Types</H2> 71 72<P>Same as <A HREF="device.html#types">Device</A>, with the following additional requirements:</P> 73 74<TABLE CELLPADDING="5" BORDER="1"> 75 <TR><TD>Category</TD><TD>A type convertible to <A HREF="../guide/traits.html#category_tags"><CODE>device_tag</CODE></A> and to <A HREF="../guide/modes.html#mode_tags"><CODE>input</CODE></A></TD></TR> 76</TABLE> 77 78<A NAME="notation"></A> 79<H2>Notation</H2> 80 81<TABLE CELLPADDING="2"> 82 <TR><TD><CODE>S</CODE></TD><TD>- A type which is a model of Source</TD></TR> 83 <TR><TD><CODE>Ch</CODE></TD><TD>- The character type</TD></TR> 84 <TR><TD><CODE>src</CODE></TD><TD>- Object of type <CODE>S</CODE></TD></TR> 85 <TR><TD><CODE>s</CODE></TD><TD>- Object of type <CODE>Ch*</CODE></SPAN></TD></TR> 86 <TR><TD><CODE>n</CODE></TD><TD>- Object of type <CODE>std::streamsize</CODE></TD></TR> 87 <TR><TD><CODE>io</CODE></TD><TD>- Alias for namespace <CODE>boost::iostreams</CODE></TD></TR> 88</TABLE> 89 90<A NAME="expressions"></A> 91<H2>Valid Expressions / Semantics</H2> 92 93<TABLE CELLPADDING="5" BORDER="1"> 94 <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Category Precondition</TH><TH>Semantics</TH></TR> 95 <TR> 96 <TD> 97 <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#char_type_of_ref">char_type_of</A><S>::type</CODE></PRE> 98 </TD> 99 <TD><CODE>typename</CODE> of the character type</TD> 100 <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> 101 </TR> 102 <TR> 103 <TD> 104 <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#category_ref">category_of</A><S>::type</CODE></PRE> 105 </TD> 106 <TD><CODE>typename</CODE> of the category</TD> 107 <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> 108 </TR> 109 <TR> 110 <TD><PRE CLASS="plain_code"><CODE><A HREF="../functions/read.html">io::read</A>(src, s, n)</CODE></PRE></TD> 111 <TD><CODE>std::streamsize</CODE></TD> 112 <TD>Not convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD> 113 <TD> 114 Reads up to <CODE>n</CODE> characters from the input sequence controlled by <CODE>dev</CODE> into <CODE>s</CODE>, returning the number of characters read, or <CODE>-1</CODE> to indicate end-of-sequence 115 </TD> 116 </TR> 117 <TR> 118 <TD><PRE CLASS="plain_code"><CODE>src.input_sequence()</CODE></PRE></TD> 119 <TD><PRE CLASS="plain_code"><CODE>std::pair<Ch*,Ch*></CODE></PRE></TD> 120 <TD>Convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD> 121 <TD>Returns a pair of pointers delimiting the sequence controlled by <CODE>src</CODE></TD> 122 </TR> 123</TABLE> 124 125<H2>Exceptions</H2> 126 127<P> 128 Errors which occur during the execution of member functions <CODE>read</CODE> or <CODE>input_sequence</CODE> are indicated by throwing exceptions. Reaching the end of the sequence is not an error. 129</P> 130 131<P> 132 After an exception is thrown, a Source must be in a consistent state; further i/o operations may throw exceptions but must have well-defined behaviour. 133</P> 134 135<H2>Models</H2> 136 137<UL> 138 <LI>Standard input streams and stream buffers. 139 <LI><A HREF="../classes/array.html#array_source"><CODE>array_source</CODE></A>, <A HREF="../classes/file.html#file_source"><CODE>file_source</CODE></A>, <A HREF="../classes/file_descriptor.html#file_descriptor_source"><CODE>file_descriptor_source</CODE></A>, <A HREF="../classes/mapped_file.html#mapped_file_source"><CODE>mapped_file_source</CODE></A>. 140</UL> 141 142<!-- Begin Footer --> 143 144<HR> 145 146<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> 147<P CLASS="copyright"> 148 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>) 149</P> 150 151<!-- End Footer --> 152 153</BODY> 154