<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <HTML> <HEAD> <TITLE>Sink</TITLE> <LINK REL="stylesheet" HREF="../../../../boost.css"> <LINK REL="stylesheet" HREF="../theme/iostreams.css"> </HEAD> <BODY> <!-- Begin Banner --> <H1 CLASS="title">Sink</H1> <HR CLASS="banner"> <!-- End Banner --> <H2>Definition</H2> <P> 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>. </P> <H2>Description</H2> <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> <OL> <LI STYLE="list-style-type:lower-roman"> 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>; </LI> <LI STYLE="list-style-type:lower-roman"> by defining a member function <CODE>output_sequence</CODE> returning a pair of pointers delimiting the sequence in its entirety. </LI> </OL> <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> <P>The mode of a Sink is <A HREF="../guide/modes.html#output"><CODE>output</CODE></A> or one of its refinements.</P> <H2>Note</H2> <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>. <H2>Example</H2> <P>A model of Sink can be defined as follows:</P> <PRE CLASS="broken_ie"><SPAN CLASS="keyword">struct</SPAN> Sink { <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="keyword">char</SPAN> char_type; <SPAN CLASS="keyword">typedef</SPAN> sink_tag category; <SPAN CLASS="keyword">void</SPAN> write(<SPAN CLASS="keyword">const</SPAN> <SPAN CLASS="keyword">char</SPAN>* s, std::streamsize n) { <SPAN CLASS="comment">// Write up to n characters from the buffer // s to the output sequence, returning the // number of characters written</SPAN> } };</PRE> <P> 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>. <H2>Refinement of</H2> <P><A HREF="device.html">Device</A>.</P> <A NAME="types"></A> <H2>Associated Types</H2> <P>Same as <A HREF="device.html#types">Device</A>, with the following additional requirements:</P> <TABLE CELLPADDING="5" BORDER="1"> <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> </TABLE> <A NAME="notation"></A> <H2>Notation</H2> <TABLE CELLPADDING="2"> <TR><TD><CODE>S</CODE></TD><TD>- A type which is a model of Sink</TD></TR> <TR><TD><CODE>Ch</CODE></TD><TD>- The character type</TD></TR> <TR><TD><CODE>snk</CODE></TD><TD>- Object of type <CODE>S</CODE></TD></TR> <TR><TD><CODE>s</CODE></TD><TD>- Object of type <CODE>const Ch*</CODE></SPAN></TD></TR> <TR><TD><CODE>n</CODE></TD><TD>- Object of type <CODE>std::streamsize</CODE></TD></TR> <TR><TD><CODE>io</CODE></TD><TD>- Alias for namespace <CODE>boost::iostreams</CODE></TD></TR> </TABLE> <A NAME="expressions"></A> <H2>Valid Expressions / Semantics</H2> <P>Same as <A HREF="device.html#types">Device</A>, with the following additional requirements:</P> <TABLE CELLPADDING="5" BORDER="1"> <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Category Precondition</TH><TH>Semantics</TH></TR> <TR> <TD> <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#char_type_of_ref">char_type_of</A><S>::type</CODE></PRE> </TD> <TD><CODE>typename</CODE> of the character type</TD> <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> </TR> <TR> <TD> <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#category_ref">category_of</A><S>::type</CODE></PRE> </TD> <TD><CODE>typename</CODE> of the category</TD> <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> </TR> <TR> <TD><PRE CLASS="plain_code"><CODE><A HREF="../functions/read.html">io::write</A>(snk, s, n)</CODE></PRE></TD> <TD><CODE>std::streamsize</CODE></TD> <TD>Not convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD> <TD> 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 </TD> </TR> <TR> <TD><PRE CLASS="plain_code"><CODE>snk.output_sequence()</CODE></PRE></TD> <TD><PRE CLASS="plain_code"><CODE>std::pair<Ch*,Ch*></CODE></PRE></TD> <TD>Convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD> <TD>Returns a pair of pointers delimiting the sequence controlled by <CODE>snk</CODE></TD> </TR> </TABLE> <H2>Exceptions</H2> <P> Errors which occur during the execution of member functions <CODE>write</CODE> or <CODE>output_sequence</CODE> are indicated by throwing exceptions. Attempting to write past the end of the sequence is always an error. </P> <P> 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. </P> <H2>Models</H2> <UL> <LI>Standard output streams and stream buffers. <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>. </UL> <!-- Begin Footer --> <HR> <P CLASS="copyright">Revised 02 Feb 2008</P> <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> <P CLASS="copyright"> 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>) </P> <!-- End Footer --> </BODY>