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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<Ch></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><F>::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><F>::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 | ||
169 | <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> | |
170 | <P CLASS="copyright"> | |
171 | 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>) | |
172 | </P> | |
173 | ||
174 | <!-- End Footer --> | |
175 | ||
176 | </BODY> |