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Last change on this file since 29 was 29, checked in by landauf, 16 years ago

updated boost from 1_33_1 to 1_34_1
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1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
2<HTML>
3<HEAD>
4    <TITLE>SeekableFilter</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">SeekableFilter</H1>
13    <HR CLASS="banner">
14
15<!-- End Banner -->
16
17<H2>Definition</H2>
18
19<P>
20    A SeekableFilter is a <A HREF="filter.html">Filter</A> whose <A HREF="../guide/modes.html">mode</A> refines <A HREF="../guide/modes.html#seekable">seekable</A>.
21</P>
22
23<H2>Description</H2>
24
25<P>
26    A SeekableFilter operates on the character sequence controlled by a <A HREF="seekable_device.html">SeekableDevice</A>, providing access to a filtered sequence having the same character type. It may expose the filtered sequence in two ways:
27    <OL>
28        <LI STYLE="list-style-type:lower-roman">
29            by defining member function <CODE>get</CODE>, <CODE>put</CODE> and <CODE>seek</CODE>.
30        </LI>
31        <LI STYLE="list-style-type:lower-roman">
32            by defining member functions <CODE>read</CODE>, <CODE>write</CODE> and <CODE>seek</CODE>.
33        </LI>
34    </OL>
35    The second alternative is provided for enhanced performance. SeekableFilters implementing this alternative are referred to as <I>Multi-Character</I>. (<I>See</I> <A HREF="multi_character.html">Multi-Character Filter</A>.)
36</P>
37
38<H2>Refinement of</H2>
39
40<P><A HREF="input_filter.html">InputFilter</A>, <A HREF="output_filter.html">OutputFilter</A>.</P>
41
42<H2>Associated Types</H2>
43
44<TABLE CELLPADDING="5" BORDER="1">
45    <TR><TD>Character type</TD><TD>The type of the characters in the filtered sequences</TD></TR>
46    <TR>
47        <TD>Category</TD>
48        <TD>
49            A type convertible to <A HREF="../guide/traits.html#category_tags"><CODE>filter_tag</CODE></A> and to <A HREF="../guide/modes.html#seekable"><CODE>seekable</CODE></A>
50        </TD>
51    </TR>
52    <TR>
53        <TD>Mode</TD>
54        <TD>
55            The unique <I>most-derived</I> <A HREF="../guide/modes.html#mode_tags">mode tag</A> to which Category is convertible
56        </TD>
57    </TR>
58</TABLE>
59
60<H2>Notation</H2>
61
62<TABLE CELLPADDING="2">
63    <TR><TD><CODE>F</CODE></TD><TD>- A type which is a model of SeekableFilter</TD></TR>
64    <TR><TD><CODE>D</CODE></TD><TD>- A type which is a model of <A HREF="device.html">Device</A>, with the same character type as <CODE>F</CODE> and with mode convertible to the mode of <CODE>F</CODE></TD></TR>
65    <TR><TD><CODE>Ch</CODE></TD><TD>- The character type of <CODE>F</CODE></TD></TR>
66    <TR><TD><CODE>Tr</CODE></A></TD><TD>- <A HREF="../classes/char_traits.html"><CODE>boost::iostreams::char_traits&lt;Ch&gt;</CODE></A></TD></TR>
67    <TR><TD><CODE>f</CODE></TD><TD>- Object of type <CODE>F</CODE></TD></TR>
68    <TR><TD><CODE>d</CODE></TD><TD>- Object of type <CODE>D</CODE></TD></TR>
69    <TR><TD><CODE>c</CODE></TD><TD>- Object of type <CODE>Ch</CODE></TD></TR>
70    <TR><TD><CODE>s1</CODE></TD><TD>- Object of type <CODE>Ch*</CODE></TD></TR>
71    <TR><TD><CODE>s2</CODE></TD><TD>- Object of type <CODE>const Ch*</CODE></TD></TR>
72    <TR><TD><CODE>n</CODE></TD><TD>- Object of type <CODE>std::streamsize</CODE></TD></TR>
73    <TR><TD><CODE>off</CODE></TD><TD>- Object of type <A HREF="../functions/positioning.html#synopsis"><CODE>stream_offset</CODE></A></TD></TR>
74    <TR><TD><CODE>way</CODE></TD><TD>- Object of type <CODE>std::ios_base::seekdir</CODE></TD></TR>
75    <TR><TD><CODE>which</CODE></TD><TD>- Object of type <CODE>std::ios_base::openmode</CODE></TD></TR>
76    <TR><TD><CODE>io</CODE></TD><TD>- Alias for namespace <CODE>boost::iostreams</CODE></TD></TR>
77</TABLE>
78
79<H2>Valid Expressions / Semantics</H2>
80
81<TABLE CELLPADDING="5" BORDER="1">
82    <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Category Precondition</TH><TH>Semantics</TH></TR>
83    <TR>
84        <TD>
85            <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#char_type_of_ref">char_type_of</A>&lt;F&gt;::type</CODE></PRE>
86        </TD>
87        <TD><CODE>typename</CODE> of the character type</TD>
88        <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD>
89    </TR>
90    <TR>
91        <TD>
92            <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#category_ref">category_of</A>&lt;F&gt;::type</CODE></PRE>
93        </TD>
94        <TD><CODE>typename</CODE> of the category</TD>
95        <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD>
96    </TR>
97    <TR>
98        <TD><PRE CLASS="plain_code"><CODE>f.get(d)</CODE></PRE></TD>
99        <TD><CODE>Tr::int_type</CODE></TD>
100        <TD ROWSPAN="2">
101            Not convertible to <A HREF="../guide/traits.html#category_tags"><CODE>multi_char_tag</CODE></A>
102        </TD>
103        <TD>
104            Returns the next character in the sequence controlled by <CODE>f</CODE>, or <CODE>Tr::eof()</CODE> if the end of the sequence has been reached. The sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/read.html"><CODE>io::read</CODE></A> and <A HREF="../functions/putback.html"><CODE>io::putback</CODE></A>.
105
106            <!-- reads up to <CODE>n</CODE> characters from the sequence controlled by <CODE>dev</CODE> into <CODE>s</CODE>, returning the number of characters read; returning a value less than n indicates end-of-sequence -->
107        </TD>
108    </TR>
109    <TR>
110        <TD><PRE CLASS="plain_code"><CODE>f.put(d, c)</CODE></PRE></TD>
111        <TD><CODE>bool</CODE></TD>
112        <TD>
113            Writes the character <CODE>c</CODE> to the sequence controlled by <CODE>f</CODE>. The sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/write.html"><CODE>io::write</CODE></A>.
114        </TD>
115    </TR>
116    <TR>
117        <TD><PRE CLASS="plain_code"><CODE>f.read(d, s1, n)</CODE></PRE></TD>
118        <TD><PRE CLASS="plain_code"><CODE>std::streamsize</CODE></PRE></TD>
119        <TD ROWSPAN="2">
120            Convertible to <A HREF="../guide/traits.html#category_tags"><CODE>multi_char_tag</CODE></A>
121        </TD>
122        <TD>
123            Reads up to <CODE></CODE> characters from the sequence controlled by <CODE>f</CODE> into the buffer <CODE>s1</CODE>, returning the number of characters read. Returning a value less than <CODE>n</CODE> indicates end-of-sequence. The sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/read.html"><CODE>io::read</CODE></A> and <A HREF="../functions/putback.html"><CODE>io::putback</CODE></A>.
124        </TD>
125    </TR>
126    <TR>
127        <TD><PRE CLASS="plain_code"><CODE>f.write(d, s2, n)</CODE></PRE></TD>
128        <TD><PRE CLASS="plain_code"><CODE>std::streamsize</CODE></PRE></TD>
129        <TD>
130            Writes n characters from the buffer <CODE>s2</CODE> to the sequence controlled by <CODE>f</CODE>. The sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/write.html"><CODE>io::write</CODE></A>.
131        </TD>
132    </TR>
133    <TR>
134        <TD><PRE CLASS="plain_code"><CODE>f.seek(d, off, way)</CODE></PRE></TD>
135        <TD><CODE>std::streampos</CODE></TD>
136        <TD ALIGN="center">-</TD>
137        <TD>
138            <P CLASS="concept">
139                Advances the read/write head by <CODE>off</CODE> characters, returning the new position, where the offset is calculated from:
140            </P>
141            <UL STYLE="margin:0,0,0,auto">
142                <LI STYLE="list-style-type:disc;list-style-image:none">the start of the sequence if <CODE>way</CODE> is <CODE>ios_base::beg</CODE>
143                <LI STYLE="list-style-type:disc;list-style-image:none">the current position if <CODE>way</CODE> is <CODE>ios_base::cur</CODE>
144                <LI STYLE="list-style-type:disc;list-style-image:none">the end of the sequence if <CODE>way</CODE> is <CODE>ios_base::end</CODE>
145            </UL>
146            <P CLASS="concept">
147                The sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/read.html"><CODE>io::seek</CODE></A> and using <A HREF="../functions/putback.html"><CODE>io::write</CODE></A> if the <A HREF="../guide/modes.html">mode</A> of <CODE>F</CODE> is convertible to <A HREF="../guide/modes.html#output"><CODE>output</CODE></A>.
148            </P>
149        </TD>
150    </TR>
151</TABLE>
152
153<H2>Exceptions</H2>
154
155<P>
156    Errors which occur during the execution of <CODE>get</CODE>, <CODE>put</CODE>, <CODE>read</CODE>, <CODE>write</CODE> or <CODE>seek</CODE> are indicated by throwing exceptions. Reaching the end of the sequence is not an error, but attempting to write past the end of the sequence is.
157</P>
158
159<P>
160    After an exception is thrown, a SeekableFilter must be in a consistent state; further i/o operations may throw exceptions but must have well-defined behaviour. Furthermore, unless it is <A HREF="closable.html">Closable</A>, it must be ready to begin processing a new character sequence.
161</P>
162
163<H2>Models</H2>
164
165<!-- Begin Footer -->
166
167<HR>
168<P CLASS="copyright">Revised
169<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
17020 May, 2004
171<!--webbot bot="Timestamp" endspan i-checksum="38504" -->
172</P>
173
174<P CLASS="copyright">&copy; Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P>
175<P CLASS="copyright"> 
176    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>)
177</P>
178
179<!-- End Footer -->
180
181</BODY>
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