boost_1_45_0/libs/iostreams/doc/concepts/sink.html - nest-learning-thermostat/5.0/boost - Git at Google

 <!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>&lt;S&gt;::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>&lt;S&gt;::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&lt;Ch*,Ch*&gt;</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">&copy; Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>&copy; 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>
	<!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>