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