1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4 <TITLE>Peekable</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">Peekable</H1> 13 <HR CLASS="banner"> 14 15<!-- End Banner --> 16 17<H2>Description</H2> 18 19<P> 20 A Peekable <A HREF="device.html">Device</A> allows a character read from the input sequence to be putback. 21</P> 22 23<P> 24 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. 25</P> 26 27<H2>Refinement of</H2> 28 29<A HREF="source.html">Source</A>. 30 31<A NAME="types"></A> 32<H2>Associated Types</H2> 33 34Same as <A HREF="source.html">Source</A>. 35 36<H2>Notation</H2> 37 38<TABLE CELLPADDING="2"> 39 <TR><TD><CODE>P</CODE></TD><TD>-</TD><TD>A type which is a model of Peekable</TD></TR> 40 <TR><TD><CODE>p</CODE></TD><TD>-</TD><TD>Object of type <CODE>P</CODE></TD></TR> 41 <TR><TD><CODE>c</CODE></TD><TD>-</TD><TD>Object of type equal to the character type of <CODE>P</CODE></TD></TR> 42 <TR><TD><CODE>io</CODE></TD><TD>-</TD><TD>Alias for namespace <CODE>boost::iostreams</CODE></TD></TR> 43</TABLE> 44 45<H2>Valid Expressions / Semantics</H2> 46 47<TABLE CELLPADDING="5" BORDER="1"> 48 <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Precondition</TH><TH>Semantics</TH><TH>Postcondition</TH></TR> 49 <TR> 50 <TD> 51 <PRE CLASS="plain_code"><CODE><A HREF="../functions/putback.html">io::putback</A>(p, c)</CODE></PRE> 52 </TD> 53 <TD><CODE>bool</CODE></TD> 54 <TD> 55 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 56 </TD> 57 <TD> 58 Attempts to put back <CODE>c</CODE> to <CODE>p</CODE>, returning <CODE>true</CODE> for success 59 </TD> 60 <TD> 61 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> 62 </TD> 63 </TR> 64</TABLE> 65 66<H2>Exceptions</H2> 67 68<P> 69 Errors which occur during the execution of <A CLASS="code" HREF="../functions/putback.html"><CODE>putback</CODE></A> are be indicated by throwing exceptions. 70</P> 71 72<H2>Models</H2> 73<UL> 74 <LI>Standard input streams and stream buffers. 75</UL> 76 77<!-- Begin Footer --> 78 79<HR> 80 81<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> 82<P CLASS="copyright"> 83 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>) 84</P> 85 86<!-- End Footer --> 87 88</BODY>