159 lines
7.3 KiB
HTML
159 lines
7.3 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>Function Template seek</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">Function Template <CODE>seek</CODE></H1>
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<HR CLASS="banner">
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<!-- End Banner -->
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<DL class="page-index">
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<DT><A href="#overview">Overview</A></DT>
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<DT><A href="#headers">Headers</A></DT>
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<DT><A href="#reference">Reference</A></DT>
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</DL>
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<A NAME="overview"></A>
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<H2>Overview</H2>
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<P>
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The function template <CODE>seek</CODE> is used by the Iostreams library to perform random access withing a sequence controlled by a <A HREF="../concepts/device.html">Device</A>.</P>
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</P>
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<A NAME="headers"></A>
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<H2>Headers</H2>
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<DL>
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<DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE><boost/iostreams/operations.hpp></CODE></A></DT>
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<DT><A CLASS="header" HREF="../../../../boost/iostreams/seek.hpp"><CODE><boost/iostreams/seek.hpp></CODE></A></DT>
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</DL>
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<A NAME="reference"></A>
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<H2>Reference</H2>
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<A NAME="description"></A>
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<H4>Description</H4>
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Repositions one or both heads within the sequence controlled by a given instance of the template parameter <CODE>T</CODE>, returning the resulting stream position.
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<A NAME="synopsis"></A>
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<H4>Synopsis</H4>
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<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
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<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>>
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std::streampos
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<A CLASS="documented" HREF="#semantics">seek</A>( T&, <A CLASS="documented" HREF="positioning.html#synopsis">stream_offset</A> <A CLASS="documented" HREF="#function_params">off</A>, std::ios_base::seekdir <A CLASS="documented" HREF="#function_params">way</A>,
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std::ios_base::openmode <A CLASS="documented" HREF="#function_params">which</A> =
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std::ios_base::in | std::ios_base::out );
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} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
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<A NAME="template_params"></A>
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<H4>Template Parameters</H4>
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<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
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<TR>
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<TR>
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<TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
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<TD>A model of one of the <A HREF="../guide/concepts.html#device_concepts">Device</A> concepts which allows random access.
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</TR>
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</TABLE>
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<A NAME="function_params"></A>
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<H4>Function Parameters</H4>
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<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
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<TR>
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<TR>
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<TD VALIGN="top"><I>off</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
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<TD>A <A HREF="positioning.html#synopsis"><CODE>stream_offset</CODE></A> indicating the number of characters by which the appropriate reading or writing heads should be advanced. The initial position is determined by the parameter <I>way</I>.
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</TR>
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<TR>
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<TD VALIGN="top"><I>way</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
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<TD><P>Determines the initial position to which the offset <I>off</I> is applied, as follows:
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<UL>
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<LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::beg</CODE>, the initial position is the begining of the stream
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<LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::cur</CODE>, the initial position is the current position
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<LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::end</CODE>, the initial position is the end of the stream
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</UL>
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</P>
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</TR>
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<TR>
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<TD VALIGN="top"><I>which</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
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<TD>Determines whether the reading head, the writing head or both are repositioned.
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</TR>
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</TABLE>
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<A NAME="semantics"></A>
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<H4>Semantics</H4>
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<P>The semantics of <CODE>seek</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P>
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<TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
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<TR><TH><CODE>category_of<T>::type</CODE></TH><TH>semantics</TH></TR>
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<TR>
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<TD VALIGN="top">convertible to <CODE>istream_tag</CODE> or <CODE>ostream_tag</CODE></TD>
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<TD>returns:
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<UL STYLE='margin-top:0'>
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<LI><CODE>t.rdbuf()->pubseekpos(<A HREF="positioning.html#offset_to_position">offset_to_position</A>(off))</CODE>, if <CODE>way</CODE> is <CODE>std::ios_base::beg</CODE> and <CODE>off</CODE> is outside the range of <CODE>std::streamoff</CODE>, and
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<LI><CODE>t.rdbuf()->pubseekoff(off, way)</CODE>, otherwise
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<UL>
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</TR>
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<TR>
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<TD VALIGN="top">convertible to <CODE>streambuf_tag</CODE></TD>
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<TD>returns:
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<UL STYLE='margin-top:0'>
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<LI><CODE>t.pubseekpos(<A HREF="positioning.html#offset_to_position">offset_to_position</A>(off))</CODE>, if <CODE>way</CODE> is <CODE>std::ios_base::beg</CODE> and <CODE>off</CODE> is outside the range of <CODE>std::streamoff</CODE>, and
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<LI><CODE>t.pubseekoff(off, way)</CODE>, otherwise
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<UL>
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</TR>
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<TR>
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<TD VALIGN="top">convertible to <CODE>input_seekable</CODE> but not to <CODE>output_seekable</CODE></TD>
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<TD>returns <CODE>t.seek(off, way)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN="top">convertible to <CODE>output_seekable</CODE> but not to <CODE>input_seekable</CODE></TD>
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<TD>returns <CODE>t.seek(off, way)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN="top">convertible to <CODE>dual_seekable</CODE> or to <CODE>bidirectional_seekable</CODE></TD>
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<TD>returns <CODE>t.seek(off, way, which)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN="top">convertible to <CODE>seekable</CODE></TD>
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<TD>returns <CODE>t.seek(off, way)</CODE></TD>
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</TR>
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<TR>
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<TD VALIGN="top"><I>otherwise</I></TD>
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<TD>compile-time error</TD>
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</TR>
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</TABLE>
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<P>In short:
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<UL>
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<LI CLASS="square">If <CODE>T</CODE> is a standard stream or stream buffer type, delegates to <CODE>std::basic_streambuf::pubseekoff</CODE> or <CODE>std::basic_streambuf::pubseekpos</CODE>, as appropriate.
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<LI CLASS="square">Otherwise, if the <A HREF="../guide/modes.html">mode</A> of <CODE>T</CODE> allows only one reading head, delegates to a member function <CODE>seek</CODE> which takes a <CODE>stream_offset</CODE> and a <CODE>seekdir</CODE> but no <CODE>openmode</CODE>.
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<LI CLASS="square">Otherwise, if the <A HREF="../guide/modes.html">mode</A> of <CODE>T</CODE> allows random access with two reading heads, delegates to a member function <CODE>seek</CODE> which takes a <CODE>stream_offset</CODE>, a <CODE>seekdir</CODE> and an <CODE>openmode</CODE>.
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<LI CLASS="square">If the <A HREF="../guide/modes.html">mode</A> of T does not permit random access, attempting to invoke <CODE>seek</CODE> is a compile-time error.
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</UL>
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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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