1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4 <TITLE>Stream Offsets</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">Stream Offsets</H1> 13 <HR CLASS="banner"> 14 15<!-- End Banner --> 16 17<DL class="page-index"> 18 <DT><A href="#overview">Overview</A></DT> 19 <DT><A href="#acknowledgments">Acknowledgments</A> 20 <DT><A href="#headers">Headers</A></DT> 21 <DT><A href="#reference">Reference</A></DT> 22</DL> 23 24<HR> 25 26<A NAME="overview"></A> 27<H2>Overview</H2> 28 29<P> 30 The header <A CLASS="header" HREF="../../../../boost/iostreams/positioning.hpp"><CODE><boost/iostreams/positioning.hpp></CODE></A> provides the definition of the integral type <CODE>boost::iostreams::stream_offset</CODE>, capable of holding arbitrary stream offsets on most platforms, together with the definition of two functions, <CODE>offset_to_position</CODE> and <CODE>position_to_offset</CODE>, for converting between <CODE>stream_offset</CODE> and <CODE>std::streampos</CODE>. 31</P> 32 33<P> 34 The type <CODE>std::streampos</CODE> is required to be able to hold an arbitrary stream position, but it is not an intergral type. Although <CODE>std::streampos</CODE> is interconvertible with the integral type <CODE>std::streamoff</CODE>, the conversion from <CODE>std::streampos</CODE> to <CODE>std::streamoff</CODE> may not be faithful for large (64-bit) values. The integral type <CODE>boost::iostreams::stream_offset</CODE> is intended as a replacement for <CODE>std::streamoff</CODE>, with the implicit conversions to and from <CODE>std::streampos</CODE> being replaced by explicit conversion functions. 35</P> 36 37<P> 38 The implementation of <CODE>offset_to_position</CODE> and <CODE>position_to_offset</CODE> relies on implementation defined behavior, and is guaranteed to work correctly for large values only for standard libraries which define <CODE>std::streamoff</CODE> to be 64-bit type or for which the Boost Iostreams library has been explicitly configured. 39</P> 40 41<A NAME="acknowledgments"></A> 42<H2>Acknowledgments</H2> 43 44<P>Gareth Sylvester-Bradley suggested the treatment of large stream offsets used by the Boost Iostreams library and supplied the implementation of <CODE>offset_to_position</CODE> and <CODE>position_to_offset</CODE> used with the Dinkumware standard library.</P> 45 46<A NAME="headers"></A> 47<H2>Headers</H2> 48 49<DL class="page-index"> 50 <DT><A CLASS="header" HREF="../../../../boost/iostreams/positioning.hpp"><CODE><boost/iostreams/positioning.hpp></CODE></A></DT> 51</DL> 52 53<A NAME="reference"></A> 54<H2>Reference</H2> 55 56<A NAME="synopsis"></A> 57<H4>Synopsis</H4> 58 59<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { 60 61<SPAN CLASS='keyword'>typedef</SPAN> <A CLASS='documented' HREF='../../../integer/doc/html/boost_integer/cstdint.html' TARGET='_top'>boost::intmax_t</A> stream_offset; 62std::streampos <A CLASS='documented' HREF='#offset_to_position'>offset_to_position</A>(stream_offset n); 63stream_offset <A CLASS='documented' HREF='#position_to_offset'>position_to_offset</A>(std::streampos pos); 64 65} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE> 66 67<A NAME="offset_to_position"></A> 68<H4>Function template <CODE>offset_to_position</CODE></H4> 69 70<PRE CLASS="broken_ie">std::streampos offset_to_position(stream_offset n);</PRE> 71 72<P>Returns a <CODE>std::streampos</CODE> representing the <CODE>n</CODE><I>th</I> position in a stream.</P> 73 74<A NAME="position_to_offset"></A> 75<H4>Function template <CODE>position_to_offset</CODE></H4> 76 77<PRE CLASS="broken_ie">stream_offset position_to_offset(std::streampos pos);</PRE> 78 79<P>Returns a <CODE>stream_offset</CODE> representing the same character position as <CODE>pos</CODE>, disregarding any code-conversion state.</P> 80 81<!-- Begin Footer --> 82 83<HR> 84 85<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> 86<P CLASS="copyright"> 87 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>) 88</P> 89 90<!-- End Footer --> 91 92</BODY>