88 lines
3.3 KiB
HTML
88 lines
3.3 KiB
HTML
<!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>Peekable</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">Peekable</H1>
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<HR CLASS="banner">
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<!-- End Banner -->
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<H2>Description</H2>
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<P>
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A Peekable <A HREF="device.html">Device</A> allows a character read from the input sequence to be putback.
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</P>
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<P>
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The name of the concept is based on the observation that a PeekableDevice allow the user to peek at the first character in the sequence it controls by calling <A HREF="../functions/get.html"><CODE>get</CODE></A> or <A HREF="../functions/read.html"><CODE>read</CODE></A> followed by <A HREF="../functions/putback.html"><CODE>putback</CODE></A>. The names Putbackable and InputRevertable were considered but rejected.
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</P>
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<H2>Refinement of</H2>
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<A HREF="source.html">Source</A>.
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<A NAME="types"></A>
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<H2>Associated Types</H2>
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Same as <A HREF="source.html">Source</A>.
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<H2>Notation</H2>
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<TABLE CELLPADDING="2">
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<TR><TD><CODE>P</CODE></TD><TD>-</TD><TD>A type which is a model of Peekable</TD></TR>
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<TR><TD><CODE>p</CODE></TD><TD>-</TD><TD>Object of type <CODE>P</CODE></TD></TR>
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<TR><TD><CODE>c</CODE></TD><TD>-</TD><TD>Object of type equal to the character type of <CODE>P</CODE></TD></TR>
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<TR><TD><CODE>io</CODE></TD><TD>-</TD><TD>Alias for namespace <CODE>boost::iostreams</CODE></TD></TR>
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</TABLE>
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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>Precondition</TH><TH>Semantics</TH><TH>Postcondition</TH></TR>
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<TR>
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<TD>
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<PRE CLASS="plain_code"><CODE><A HREF="../functions/putback.html">io::putback</A>(p, c)</CODE></PRE>
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</TD>
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<TD><CODE>bool</CODE></TD>
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<TD>
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One or more characters has been read from <CODE>p</CODE> using <A HREF="../functions/get.html"><CODE>io::get</CODE></A> or <A HREF="../functions/read.html"><CODE>io::read</CODE></A>, with no intervening i/o operations having been performed
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</TD>
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<TD>
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Attempts to put back <CODE>c</CODE> to <CODE>p</CODE>, returning <CODE>true</CODE> for success
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</TD>
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<TD>
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If putback returns <CODE>true</CODE>, the next character read from <CODE>p</CODE> using <A HREF="../functions/get.html"><CODE>io::get</CODE></A> or <A HREF="../functions/read.html"><CODE>io::read</CODE></A> will be equal to <CODE>c</CODE></A>
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</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 <A CLASS="code" HREF="../functions/putback.html"><CODE>putback</CODE></A> are be indicated by throwing exceptions.
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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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</UL>
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<!-- Begin Footer -->
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<HR>
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<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>
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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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