1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4 <TITLE>BidirectionalFilter</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">BidirectionalFilter</H1> 13 <HR CLASS="banner"> 14 15<!-- End Banner --> 16 17<H2>Definition</H2> 18 19<P> 20 An BidirectionalFilter is a <A HREF="filter.html">Filter</A> whose <A HREF="../guide/modes.html">mode</A> refines <A HREF="../guide/modes.html#bidirectional"><CODE>bidirectional</CODE></A>. 21</P> 22 23<H2>Description</H2> 24 25<P> 26 An BidirectionalFilter operates on the character sequences controlled by a <A HREF="bidirectional_device.html">BidirectionalDevice</A>, providing access to two filtered sequences having the same character type. It may expose the filtered sequences in two ways: 27 <OL> 28 <LI STYLE="list-style-type:lower-roman"> 29 by defining member function <CODE>get</CODE> and <CODE>put</CODE>. 30 </LI> 31 <LI STYLE="list-style-type:lower-roman"> 32 by defining member functions <CODE>read</CODE> and <CODE>write</CODE>. 33 </LI> 34 </OL> 35 The second alternative is provided for enhanced performance. BidirectionalFilters implementing this alternative are referred to as <A HREF="multi_character.html">Multi-Character Filters</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#bidirectional"><CODE>bidirectional</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 BidirectionalFilter</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 refining 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>io</CODE></TD><TD>- Alias for namespace <CODE>boost::iostreams</CODE></TD></TR> 74</TABLE> 75 76<H2>Valid Expressions / Semantics</H2> 77 78<TABLE CELLPADDING="5" BORDER="1"> 79 <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Category Precondition</TH><TH>Semantics</TH></TR> 80 <TR> 81 <TD> 82 <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#char_type_of_ref">char_type_of</A><F>::type</CODE></PRE> 83 </TD> 84 <TD><CODE>typename</CODE> of the character type</TD> 85 <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> 86 </TR> 87 <TR> 88 <TD> 89 <PRE CLASS="plain_code"><CODE>typename <A HREF="../guide/traits.html#category_ref">category_of</A><F>::type</CODE></PRE> 90 </TD> 91 <TD><CODE>typename</CODE> of the category</TD> 92 <TD ALIGN="center">-</TD><TD ALIGN="center">-</TD> 93 </TR> 94 <TR> 95 <TD><PRE CLASS="plain_code"><CODE>f.get(d)</CODE></PRE></TD> 96 <TD><CODE>Tr::int_type</CODE></TD> 97 <TD ROWSPAN="2"> 98 Convertible to <A HREF="../guide/modes.html#mode_tags"><CODE>input</CODE></A> but not to <A HREF="../guide/traits.html#category_tags"><CODE>multichar_tag</CODE></A> 99 </TD> 100 <TD> 101 Returns the next character in the input sequence controlled by <CODE>f</CODE>, <CODE>Tr::eof()</CODE> if the end of the sequence has been reached or <CODE>Tr::would_block()</CODE> if input is temporarily unavilable because a call to <CODE>d</CODE> has produced fewer characters than requested. The input sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/get.html"><CODE>io::get</CODE></A>, <A HREF="../functions/read.html"><CODE>io::read</CODE></A> and <A HREF="../functions/putback.html"><CODE>io::putback</CODE></A>. 102 </TD> 103 </TR> 104 <TR> 105 <TD><PRE CLASS="plain_code"><CODE>f.put(d, c)</CODE></PRE></TD> 106 <TD><CODE>bool</CODE></TD> 107 <TD> 108 Attempts to writes the character <CODE>c</CODE> to the output sequence controlled by <CODE>f</CODE>, returning <CODE>false</CODE> if <CODE>c</CODE> cannot be consumed because a call to <CODE>d</CODE> has consumed fewer characters than requested. The output sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/put.html"><CODE>io::put</CODE></A> and <A HREF="../functions/write.html"><CODE>io::write</CODE></A>. 109 </TD> 110 </TR> 111 <TR> 112 <TD><PRE CLASS="plain_code"><CODE>f.read(d, s1, n)</CODE></PRE></TD> 113 <TD><PRE CLASS="plain_code"><CODE>std::streamsize</CODE></PRE></TD> 114 <TD ROWSPAN="2"> 115 Convertible to <A HREF="../guide/modes.html#mode_tags"><CODE>input</CODE></A> and to <A HREF="../guide/traits.html#category_tags"><CODE>multichar_tag</CODE></A> 116 </TD> 117 <TD> 118 Reads up to <CODE>n</CODE> characters from the input sequence controlled by <CODE>f</CODE> into the buffer <CODE>s1</CODE>, returning the number of characters read or <CODE>-1</CODE> to indicate end-of-sequence. A value less than <CODE>n</CODE> may be returned only at end-of-sequence or if input is temporarily unavilable because a call to <CODE>d</CODE> has produced fewer characters than requested. The input sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/get.html"><CODE>io::get</CODE></A>, <A HREF="../functions/read.html"><CODE>io::read</CODE></A> and <A HREF="../functions/putback.html"><CODE>io::putback</CODE></A>. 119 </TD> 120 </TR> 121 <TR> 122 <TD><PRE CLASS="plain_code"><CODE>f.write(d, s2, n)</CODE></PRE></TD> 123 <TD><PRE CLASS="plain_code"><CODE>std::streamsize</CODE></PRE></TD> 124 <TD> 125 Writes up to <CODE>n</CODE> characters from the buffer <CODE>s2</CODE> to the output sequence controlled by <CODE>d</CODE>, returning the number of characters written. A value less than <CODE>n</CODE> may be returned only if a call to <CODE>d</CODE> has consumed fewer characters than requested. The output sequence controlled by <CODE>d</CODE> may be accessed using <A HREF="../functions/put.html"><CODE>io::put</CODE></A> and <A HREF="../functions/write.html"><CODE>io::write</CODE></A>. 126 </TD> 127 </TR> 128</TABLE> 129 130<H2>Exceptions</H2> 131 132<P> 133 Errors which occur during the execution of <CODE>get</CODE>, <CODE>put</CODE>, <CODE>read</CODE> or <CODE>write</CODE> are indicated by throwing exceptions. Reaching the end of the input sequence is not an error, but attempting to write past the end of the output sequence is. 134</P> 135 136<P> 137 After an exception is thrown, an BidirectionalFilter 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. 138</P> 139 140 141<H2>Models</H2> 142 143<!-- Begin Footer --> 144 145<HR> 146 147<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> 148<P CLASS="copyright"> 149 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>) 150</P> 151 152<!-- End Footer --> 153 154</BODY> 155