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    <TITLE>Function Template seek</TITLE>
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    <H1 CLASS="title">Function Template <CODE>seek</CODE></H1>
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<DL class="page-index">
  <DT><A href="#overview">Overview</A></DT>
  <DT><A href="#headers">Headers</A></DT>
  <DT><A href="#reference">Reference</A></DT>
</DL>

<A NAME="overview"></A>
<H2>Overview</H2>

<P>
    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>
</P>

<A NAME="headers"></A>
<H2>Headers</H2>

<DL>
  <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE>&lt;boost/iostreams/operations.hpp&gt;</CODE></A></DT>
  <DT><A CLASS="header" HREF="../../../../boost/iostreams/seek.hpp"><CODE>&lt;boost/iostreams/seek.hpp&gt;</CODE></A></DT>
</DL>

<A NAME="reference"></A>
<H2>Reference</H2>

<A NAME="description"></A>
<H4>Description</H4>

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.

<A NAME="synopsis"></A>
<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
              
<SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>&gt;
std::streampos 
<A CLASS="documented" HREF="#semantics">seek</A>( T&amp;, <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>,
      std::ios_base::openmode <A CLASS="documented" HREF="#function_params">which</A> =
          std::ios_base::in | std::ios_base::out );

} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>

<A NAME="template_params"></A>
<H4>Template Parameters</H4>

<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
<TR>
    <TR>
        <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>A model of one of the <A HREF="../guide/concepts.html#device_concepts">Device</A> concepts which allows random access.
    </TR>
</TABLE>

<A NAME="function_params"></A>
<H4>Function Parameters</H4>

<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
<TR>
    <TR>
        <TD VALIGN="top"><I>off</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <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>.
    </TR>
    <TR>
        <TD VALIGN="top"><I>way</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD><P>Determines the initial position to which the offset <I>off</I> is applied, as follows:
            <UL>
                <LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::beg</CODE>, the initial position is the begining of the stream
                <LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::cur</CODE>, the initial position is the current position
                <LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::end</CODE>, the initial position is the end of the stream
            </UL>
            </P>
    </TR>
    <TR>
        <TD VALIGN="top"><I>which</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>Determines whether the reading head, the writing head or both are repositioned.
    </TR>
</TABLE>

<A NAME="semantics"></A>
<H4>Semantics</H4>

<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>

<TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
    <TR><TH><CODE>category_of&lt;T&gt;::type</CODE></TH><TH>semantics</TH></TR>
    <TR>
        <TD VALIGN="top">convertible to <CODE>istream_tag</CODE> or <CODE>ostream_tag</CODE></TD>
        <TD>returns:
        <UL STYLE='margin-top:0'>
            <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
            <LI><CODE>t.rdbuf()->pubseekoff(off, way)</CODE>, otherwise
        <UL>
    </TR>
    <TR>
        <TD VALIGN="top">convertible to <CODE>streambuf_tag</CODE></TD>
        <TD>returns:
        <UL STYLE='margin-top:0'>
            <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
            <LI><CODE>t.pubseekoff(off, way)</CODE>, otherwise
        <UL>
    </TR>
    <TR>
        <TD VALIGN="top">convertible to <CODE>input_seekable</CODE> but not to <CODE>output_seekable</CODE></TD>
        <TD>returns <CODE>t.seek(off, way)</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">convertible to <CODE>output_seekable</CODE> but not to <CODE>input_seekable</CODE></TD>
        <TD>returns <CODE>t.seek(off, way)</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">convertible to <CODE>dual_seekable</CODE> or to <CODE>bidirectional_seekable</CODE></TD>
        <TD>returns <CODE>t.seek(off, way, which)</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">convertible to <CODE>seekable</CODE></TD>
        <TD>returns <CODE>t.seek(off, way)</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top"><I>otherwise</I></TD>
        <TD>compile-time error</TD>
    </TR>
</TABLE>

<P>In short:
<UL>
    <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.
    <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>.
    <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>.
    <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.
</UL>

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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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