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2 | <HTML> | |
3 | <HEAD> | |
4 | <TITLE>Function Template seek</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">Function Template <CODE>seek</CODE></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="#headers">Headers</A></DT> | |
20 | <DT><A href="#reference">Reference</A></DT> | |
21 | </DL> | |
22 | ||
23 | <A NAME="overview"></A> | |
24 | <H2>Overview</H2> | |
25 | ||
26 | <P> | |
27 | 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> | |
28 | </P> | |
29 | ||
30 | <A NAME="headers"></A> | |
31 | <H2>Headers</H2> | |
32 | ||
33 | <DL> | |
34 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE><boost/iostreams/operations.hpp></CODE></A></DT> | |
35 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/seek.hpp"><CODE><boost/iostreams/seek.hpp></CODE></A></DT> | |
36 | </DL> | |
37 | ||
38 | <A NAME="reference"></A> | |
39 | <H2>Reference</H2> | |
40 | ||
41 | <A NAME="description"></A> | |
42 | <H4>Description</H4> | |
43 | ||
44 | 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. | |
45 | ||
46 | <A NAME="synopsis"></A> | |
47 | <H4>Synopsis</H4> | |
48 | ||
49 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { | |
50 | ||
51 | <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>> | |
52 | std::streampos | |
53 | <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>, | |
54 | std::ios_base::openmode <A CLASS="documented" HREF="#function_params">which</A> = | |
55 | std::ios_base::in | std::ios_base::out ); | |
56 | ||
57 | } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE> | |
58 | ||
59 | <A NAME="template_params"></A> | |
60 | <H4>Template Parameters</H4> | |
61 | ||
62 | <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> | |
63 | <TR> | |
64 | <TR> | |
65 | <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> | |
66 | <TD>A model of one of the <A HREF="../guide/concepts.html#device_concepts">Device</A> concepts which allows random access. | |
67 | </TR> | |
68 | </TABLE> | |
69 | ||
70 | <A NAME="function_params"></A> | |
71 | <H4>Function Parameters</H4> | |
72 | ||
73 | <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> | |
74 | <TR> | |
75 | <TR> | |
76 | <TD VALIGN="top"><I>off</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> | |
77 | <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>. | |
78 | </TR> | |
79 | <TR> | |
80 | <TD VALIGN="top"><I>way</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> | |
81 | <TD><P>Determines the initial position to which the offset <I>off</I> is applied, as follows: | |
82 | <UL> | |
83 | <LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::beg</CODE>, the initial position is the begining of the stream | |
84 | <LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::cur</CODE>, the initial position is the current position | |
85 | <LI CLASS="square">if <I>way</I> is <CODE>std::ios_base::end</CODE>, the initial position is the end of the stream | |
86 | </UL> | |
87 | </P> | |
88 | </TR> | |
89 | <TR> | |
90 | <TD VALIGN="top"><I>which</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> | |
91 | <TD>Determines whether the reading head, the writing head or both are repositioned. | |
92 | </TR> | |
93 | </TABLE> | |
94 | ||
95 | <A NAME="semantics"></A> | |
96 | <H4>Semantics</H4> | |
97 | ||
98 | <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> | |
99 | ||
100 | <TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4> | |
101 | <TR><TH><CODE>category_of<T>::type</CODE></TH><TH>semantics</TH></TR> | |
102 | <TR> | |
103 | <TD VALIGN="top">convertible to <CODE>istream_tag</CODE> or <CODE>ostream_tag</CODE></TD> | |
104 | <TD>returns: | |
105 | <UL STYLE='margin-top:0'> | |
106 | <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 | |
107 | <LI><CODE>t.rdbuf()->pubseekoff(off, way)</CODE>, otherwise | |
108 | <UL> | |
109 | </TR> | |
110 | <TR> | |
111 | <TD VALIGN="top">convertible to <CODE>streambuf_tag</CODE></TD> | |
112 | <TD>returns: | |
113 | <UL STYLE='margin-top:0'> | |
114 | <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 | |
115 | <LI><CODE>t.pubseekoff(off, way)</CODE>, otherwise | |
116 | <UL> | |
117 | </TR> | |
118 | <TR> | |
119 | <TD VALIGN="top">convertible to <CODE>input_seekable</CODE> but not to <CODE>output_seekable</CODE></TD> | |
120 | <TD>returns <CODE>t.seek(off, way)</CODE></TD> | |
121 | </TR> | |
122 | <TR> | |
123 | <TD VALIGN="top">convertible to <CODE>output_seekable</CODE> but not to <CODE>input_seekable</CODE></TD> | |
124 | <TD>returns <CODE>t.seek(off, way)</CODE></TD> | |
125 | </TR> | |
126 | <TR> | |
127 | <TD VALIGN="top">convertible to <CODE>dual_seekable</CODE> or to <CODE>bidirectional_seekable</CODE></TD> | |
128 | <TD>returns <CODE>t.seek(off, way, which)</CODE></TD> | |
129 | </TR> | |
130 | <TR> | |
131 | <TD VALIGN="top">convertible to <CODE>seekable</CODE></TD> | |
132 | <TD>returns <CODE>t.seek(off, way)</CODE></TD> | |
133 | </TR> | |
134 | <TR> | |
135 | <TD VALIGN="top"><I>otherwise</I></TD> | |
136 | <TD>compile-time error</TD> | |
137 | </TR> | |
138 | </TABLE> | |
139 | ||
140 | <P>In short: | |
141 | <UL> | |
142 | <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. | |
143 | <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>. | |
144 | <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>. | |
145 | <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. | |
146 | </UL> | |
147 | ||
148 | <!-- Begin Footer --> | |
149 | ||
150 | <HR> | |
151 | ||
152 | <P CLASS="copyright">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a></P> | |
153 | <P CLASS="copyright"> | |
154 | 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>) | |
155 | </P> | |
156 | ||
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