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156 lines
6.3 KiB
HTML
Executable File
156 lines
6.3 KiB
HTML
Executable File
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML>
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<HEAD>
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<TITLE>Source</TITLE>
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<LINK REL="stylesheet" HREF="../../../../boost.css">
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<LINK REL="stylesheet" HREF="../theme/iostreams.css">
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</HEAD>
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<BODY>
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<!-- Begin Banner -->
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<H1 CLASS="title">Source</H1>
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<HR CLASS="banner">
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<!-- End Banner -->
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<H2>Definition</H2>
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<P>
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A Source is a <A HREF="device.html">Device</A> whose <A HREF="../modes.html">i/o mode</A> refines <A HREF="../modes.html#input">input</A>.
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</P>
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<H2>Description</H2>
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<P>
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A Source provides read-access to a sequence of characters of a given type. A Source may expose this sequence in three ways:
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<OL>
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<LI STYLE="list-style-type:lower-roman">
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by defining a member function <CODE>read</CODE>, invoked indirectly by the Iostreams Library through the function <A HREF="../functions/read.html"><CODE>boost::iostreams::read</CODE></A>;
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</LI>
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<LI STYLE="list-style-type:lower-roman">
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by overloading or specializing <A HREF="../functions/read.html"><CODE>boost::iostreams::read</CODE></A>; or
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</LI>
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<LI STYLE="list-style-type:lower-roman">
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by defining a member function <CODE>input_sequence</CODE> returning a pair of pointers delimiting the sequence in its entirety.
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</LI>
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</OL>
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</P>
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<P>The i/o mode of a Source is <A HREF="../modes.html#input">input</A> or one of its refinements.</P>
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<H2>Example</H2>
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<P>
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A model of Source can be defined as follows:
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</P>
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<PRE CLASS="broken_ie"><SPAN CLASS="keyword">struct</SPAN> Source {
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<SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="keyword">char</SPAN> char_type;
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<SPAN CLASS="keyword">typedef</SPAN> source_tag category;
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std::streamsize read(<SPAN CLASS="keyword">char</SPAN>* s, std::streamsize n)
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{
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<SPAN CLASS="comment">// Reads up to n characters from the controlled
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// sequence into the buffer s, returning the number
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// of characters read. Returning a value less than n
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// indicates end-of-sequence.</SPAN>
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}
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};</PRE>
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<P>
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Here <CODE>source_tag</CODE> is a <A HREF="../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#source"><CODE>source</CODE></A> or <A HREF="../classes/device.html#wsource"><CODE>wsource</CODE></A> and defining a member function <CODE>read</CODE>.
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<H2>Refinement of</H2>
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<P><A HREF="device.html">Device</A>.</P>
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<A NAME="types"></A>
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<H2>Associated Types</H2>
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<P>Same as <A HREF="device.html#types">Device</A>, with the following additional requirements:</P>
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<TABLE CELLPADDING="5" BORDER="1">
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<TR><TD>Category</TD><TD>A type convertible to <A HREF="../traits.html#category_tags"><CODE>device_tag</CODE></A> and to <A HREF="../modes.html#mode_tags"><CODE>input</CODE></A></TD></TR>
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</TABLE>
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<A NAME="notation"></A>
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<H2>Notation</H2>
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<TABLE CELLPADDING="2">
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<TR><TD><CODE>S</CODE></TD><TD>- A type which is a model of Source</TD></TR>
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<TR><TD><CODE>Ch</CODE></TD><TD>- The character type</TD></TR>
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<TR><TD><CODE>src</CODE></TD><TD>- Object of type <CODE>S</CODE></TD></TR>
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<TR><TD><CODE>s</CODE></TD><TD>- Object of type <CODE>Ch*</CODE></SPAN></TD></TR>
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<TR><TD><CODE>n</CODE></TD><TD>- Object of type <CODE>std::streamsize</CODE></TD></TR>
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</TABLE>
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<A NAME="expressions"></A>
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<H2>Valid Expressions / Semantics</H2>
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<TABLE CELLPADDING="5" BORDER="1">
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<TR><TH>Expression</TH><TH>Expression Type</TH><TH>Category Precondition</TH><TH>Semantics</TH></TR>
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<TR>
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<TD>
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<PRE CLASS="plain_code"><CODE>typename <A HREF="../traits.html">char_type_of</A><S>::type</CODE></PRE>
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</TD>
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<TD><CODE>typename</CODE> of the character type</TD>
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<TD ALIGN="center">-</TD><TD ALIGN="center">-</TD>
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</TR>
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<TR>
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<TD>
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<PRE CLASS="plain_code"><CODE>typename <A HREF="../traits.html">category_of</A><S>::type</CODE></PRE>
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</TD>
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<TD><CODE>typename</CODE> of the category</TD>
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<TD ALIGN="center">-</TD><TD ALIGN="center">-</TD>
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</TR>
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<TR>
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<TD><PRE CLASS="plain_code"><CODE><A HREF="../functions/read.html">boost::iostreams::read</A>(src, s, n)</CODE></PRE></TD>
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<TD><CODE>std::streamsize</CODE></TD>
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<TD>Not convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD>
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<TD>
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Reads up to <CODE>n</CODE> characters from the sequence controlled by <CODE>src</CODE> into <CODE>s</CODE>, returning the number of characters read; returning a value less than n indicates end-of-sequence
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</TD>
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</TR>
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<TR>
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<TD><PRE CLASS="plain_code"><CODE>src.input_sequence()</CODE></PRE></TD>
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<TD><PRE CLASS="plain_code"><CODE>std::pair<Ch*,Ch*></CODE></PRE></TD>
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<TD>Convertible to <A HREF="direct.html"><CODE>direct_tag</CODE></A></TD>
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<TD>Returns a pair of pointers delimiting the sequence controlled by <CODE>src</CODE></TD>
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</TR>
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</TABLE>
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<H2>Exceptions</H2>
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<P>
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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.
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</P>
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<P>
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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.
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</P>
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<H2>Models</H2>
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<UL>
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<LI>Standard input streams and stream buffers.
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<LI><A HREF="../classes/array.html#array_source">array_source</A>, <A HREF="../classes/file.html#file_source">basic_file_source</A>, <A HREF="../classes/file_descriptor.html#file_descriptor_source">file_descriptor_source</A>, <A HREF="../classes/mapped_file.html#mapped_file_source">mapped_file_source</A>.
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</UL>
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<!-- Begin Footer -->
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<HR>
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<P CLASS="copyright">Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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20 May, 2004
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<!--webbot bot="Timestamp" endspan i-checksum="38504" -->
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</P>
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<P CLASS="copyright">© Copyright Jonathan Turkanis, 2004</P>
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<P CLASS="copyright">
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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>)
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</P>
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<!-- End Footer -->
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</BODY>
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