ceph/src/boost/libs/iostreams/doc/functions/positioning.html

   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>&lt;boost/iostreams/positioning.hpp&gt;</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>&lt;boost/iostreams/positioning.hpp&gt;</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;
  62 std::streampos <A CLASS='documented' HREF='#offset_to_position'>offset_to_position</A>(stream_offset n);
  63 stream_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">&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>
  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>