| 1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
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| 2 | <HTML> |
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| 3 | <HEAD> |
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| 4 | <TITLE>Stream Offsets</TITLE> |
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| 5 | <LINK REL="stylesheet" HREF="../../../../boost.css"> |
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| 6 | <LINK REL="stylesheet" HREF="../theme/iostreams.css"> |
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| 7 | </HEAD> |
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| 8 | <BODY> |
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| 9 | |
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| 10 | <!-- Begin Banner --> |
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| 11 | |
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| 12 | <H1 CLASS="title">Stream Offsets</H1> |
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| 13 | <HR CLASS="banner"> |
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| 14 | |
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| 15 | <!-- End Banner --> |
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| 16 | |
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| 17 | <DL class="page-index"> |
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| 18 | <DT><A href="#overview">Overview</A></DT> |
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| 19 | <DT><A href="#acknowledgments">Acknowledgments</A> |
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| 20 | <DT><A href="#headers">Headers</A></DT> |
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| 21 | <DT><A href="#reference">Reference</A></DT> |
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| 22 | </DL> |
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| 23 | |
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| 24 | <HR> |
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| 25 | |
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| 26 | <A NAME="overview"></A> |
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| 27 | <H2>Overview</H2> |
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| 28 | |
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| 29 | <P> |
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| 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>. |
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| 31 | </P> |
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| 32 | |
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| 33 | <P> |
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| 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. |
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| 35 | </P> |
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| 36 | |
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| 37 | <P> |
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| 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. |
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| 39 | </P> |
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| 40 | |
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| 41 | <A NAME="acknowledgments"></A> |
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| 42 | <H2>Acknowledgments</H2> |
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| 43 | |
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| 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> |
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| 45 | |
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| 46 | <A NAME="headers"></A> |
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| 47 | <H2>Headers</H2> |
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| 48 | |
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| 49 | <DL class="page-index"> |
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| 50 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/positioning.hpp"><CODE><boost/iostreams/positioning.hpp></CODE></A></DT> |
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| 51 | </DL> |
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| 52 | |
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| 53 | <A NAME="reference"></A> |
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| 54 | <H2>Reference</H2> |
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| 55 | |
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| 56 | <A NAME="synopsis"></A> |
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| 57 | <H4>Synopsis</H4> |
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| 58 | |
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| 59 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { |
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| 60 | |
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| 61 | <SPAN CLASS='keyword'>typedef</SPAN> <A CLASS='documented' HREF='../../../integer/cstdint.htm' TARGET='_top'>boost::intmax_t</A> stream_offset; |
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| 62 | std::streampos <A CLASS='documented' HREF='#offset_to_position'>offset_to_position</A>(stream_offset n); |
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| 63 | stream_offset <A CLASS='documented' HREF='#position_to_offset'>position_to_offset</A>(std::streampos pos); |
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| 64 | |
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| 65 | } } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE> |
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| 66 | |
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| 67 | <A NAME="offset_to_position"></A> |
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| 68 | <H4>Function template <CODE>offset_to_position</CODE></H4> |
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| 69 | |
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| 70 | <PRE CLASS="broken_ie">std::streampos offset_to_position(stream_offset n);</PRE> |
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| 71 | |
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| 72 | <P>Returns a <CODE>std::streampos</CODE> representing the <CODE>n</CODE><I>th</I> position in a stream.</P> |
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| 73 | |
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| 74 | <A NAME="position_to_offset"></A> |
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| 75 | <H4>Function template <CODE>position_to_offset</CODE></H4> |
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| 76 | |
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| 77 | <PRE CLASS="broken_ie">stream_offset position_to_offset(std::streampos pos);</PRE> |
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| 78 | |
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| 79 | <P>Returns a <CODE>stream_offset</CODE> representing the same character position as <CODE>pos</CODE>, disregarding any code-conversion state.</P> |
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| 80 | |
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| 81 | <!-- Begin Footer --> |
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| 82 | |
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| 83 | <HR> |
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| 84 | <P CLASS="copyright">Revised |
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| 85 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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| 86 | 20 May, 2004 |
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| 87 | <!--webbot bot="Timestamp" endspan i-checksum="38504" --> |
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| 88 | </P> |
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| 89 | |
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| 90 | <P CLASS="copyright">© Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P> |
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| 91 | <P CLASS="copyright"> |
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| 92 | 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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| 93 | </P> |
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| 94 | |
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| 95 | <!-- End Footer --> |
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| 96 | |
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| 97 | </BODY> |
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