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1 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
2 | <HTML> | |
3 | <HEAD> | |
4 | <TITLE>Function Template flush</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>flush</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></A> | |
24 | <H2>Overview</H2> | |
25 | ||
26 | <P> | |
27 | The function template <CODE>flush</CODE> attemps to flush all buffered characters downstream. It is provided to facilite modifiying a filter chain in the middle of a sequence of output operations; specifically, it is used to implement the function <CODE>strict_sync</CODE> (<I>see</I>, <I>e.g.</I>, <A HREF='../classes/filtering_stream.html#strict_sync'><CODE>filtering_stream::strict_sync</CODE></A>). If <CODE>strict_sync</CODE> succeeds, the auto-close feature of a filter chain can be safely disabled using <CODE>set_auto_close(false)</CODE> (<I>see</I>, <I>e.g.</I>, <A HREF='../classes/filtering_stream.html#set_auto_close'><CODE>filtering_stream::set_auto_close</CODE></A>). Filters can then be added to or removed from the chain with the knowledge that no characters remain buffered. | |
28 | </P> | |
29 | <P> | |
30 | For non-<A HREF='../concepts/flushable.html'>Flushable</A> devices, <CODE>flush</CODE> returns <CODE>true</CODE>, indicating that no error has occurred.<A CLASS='footnote_ref' NAME='note_1_ref' HREF="#note_1"><SUP>[1]</SUP></A> For non-<A HREF='../concepts/flushable.html'>Flushable</A> filters, however, <CODE>flush</CODE> returns <CODE>false</CODE>, indicating that some characters may remain buffered. | |
31 | </P> | |
32 | <P> | |
33 | When working with Devices, <CODE>flush</CODE> may be used as a generic version of <CODE>std::basic_ostream::flush()</CODE>. | |
34 | </P> | |
35 | ||
36 | <A NAME="headers"></A> | |
37 | <H2>Headers</H2> | |
38 | ||
39 | <DL> | |
40 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/flush.hpp"><CODE><boost/iostreams/flush.hpp></CODE></A></DT> | |
41 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE><boost/iostreams/operations.hpp></CODE></A></DT> | |
42 | </DL> | |
43 | ||
44 | <A NAME="reference"></A> | |
45 | <H2>Reference</H2> | |
46 | ||
47 | <A NAME="description"></A> | |
48 | <H4>Description</H4> | |
49 | ||
50 | <P>Attempts to flush all buffered characters downstream. For <A HREF='../concepts/device.html'>Devices</A>, returns <CODE>true</CODE> unless an error occurs.<A CLASS='footnote_ref' NAME='note_1_ref2' HREF='#note_1'><SUP>[1]</SUP></A>. For <A HREF='../concepts/filter.html'>Filters</A>, returns <CODE>true</CODE> only if all buffered characters were successfully written to <CODE>snk</CODE>. </P> | |
51 | ||
52 | <A NAME="synopsis"></A> | |
53 | <H4>Synopsis</H4> | |
54 | ||
55 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { | |
56 | ||
57 | <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>> | |
58 | <SPAN CLASS='keyword'>bool</SPAN> <A CLASS="documented" HREF="#flush_device">flush</A>(T& t); | |
59 | ||
60 | <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>, <SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">Sink</A>> | |
61 | <SPAN CLASS='keyword'>bool</SPAN> <A CLASS="documented" HREF="#flush_filter">flush</A>(T& t, Sink& snk); | |
62 | ||
63 | } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE> | |
64 | ||
65 | <A NAME="template_params"></A> | |
66 | <H4>Template Parameters</H4> | |
67 | ||
68 | <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> | |
69 | <TR> | |
70 | <TR> | |
71 | <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> | |
72 | <TD>For the first overload, a model of <A HREF="../concepts/device.html">Device</A>; for the second overload, a model of <A HREF="../concepts/filter.html">Filter</A>. | |
73 | </TR> | |
74 | <TR> | |
75 | <TD VALIGN="top"><I>Sink</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> | |
76 | <TD>A model of <A HREF="../concepts/sink.html">Sink</A> with the same <A HREF="../guide/traits.html#char_type">character type</A> as <CODE>T</CODE>. | |
77 | </TR> | |
78 | </TABLE> | |
79 | ||
80 | <A NAME="flush_device"></A> | |
81 | <H4>Semantics — Device Types</H4> | |
82 | ||
83 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T> | |
84 | <SPAN CLASS='keyword'>bool</SPAN> flush(T& t);</PRE> | |
85 | ||
86 | <P>The semantics of <CODE>flush</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P> | |
87 | ||
88 | <TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4> | |
89 | <TR><TH><CODE>category_of<T>::type</CODE></TH><TH>semantics</TH></TR> | |
90 | <TR> | |
91 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>ostream_tag</CODE></A></TD> | |
92 | <TD>Invokes <CODE>t.rdbuf()->pubsync()</CODE> and returns <CODE>true</CODE> if the operation succeeds.</TD> | |
93 | </TR> | |
94 | <TR> | |
95 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>streambuf_tag</CODE></A> but not to <A HREF="../guide/traits.html#category_tags"><CODE>istream_tag</CODE></A></TD> | |
96 | <TD>Invokes <CODE>t.pubsync()</CODE> and returns <CODE>true</CODE> if the operation succeeds.</CODE></TD> | |
97 | </TR> | |
98 | <TR> | |
99 | <TD VALIGN="top"><I>not</I> convertible to <A HREF="../guide/traits.html#category_tags"><CODE>flushable_tag</CODE></A></TD> | |
100 | <TD>returns <CODE>t.flush()</CODE></TD> | |
101 | </TR> | |
102 | <TR> | |
103 | <TD VALIGN="top">otherwise</TD> | |
104 | <TD>returns <CODE>true</CODE></TD> | |
105 | </TR> | |
106 | </TABLE> | |
107 | ||
108 | <A NAME="flush_filter"></A> | |
109 | <H4>Semantics — Filter Types</H4> | |
110 | ||
111 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T, <SPAN CLASS="keyword">typename</SPAN> Sink> | |
112 | <SPAN CLASS='keyword'>bool</SPAN> flush(T& t, Sink& snk);</PRE> | |
113 | ||
114 | <P>The semantics of <CODE>flush</CODE> depends on the <A HREF="../guide/traits.html#category">category</A> of <CODE>T</CODE> as follows:</P> | |
115 | ||
116 | <TABLE STYLE="margin-bottom:2em;margin-left:2em" BORDER=1 CELLPADDING=4> | |
117 | <TR><TH><CODE>category_of<T>::type</CODE></TH><TH>semantics</TH></TR> | |
118 | <TR> | |
119 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>flushable_tag</CODE></A></TD> | |
120 | <TD>returns <CODE>t.flush(snk)</CODE></TD> | |
121 | </TR> | |
122 | <TR> | |
123 | <TD VALIGN="top">otherwise</TD> | |
124 | <TD>returns <CODE>false</CODE></TD> | |
125 | </TR> | |
126 | </TABLE> | |
127 | ||
128 | <!-- Begin Footnotes --> | |
129 | ||
130 | <HR> | |
131 | ||
132 | <P> | |
133 | <A CLASS='footnote_ref' NAME='note_1' HREF='#note_1_ref'><SUP>[1]</SUP></A>It was noticed late in developement that to be consistent with the policy of reporting errors using exceptions (<I>see</I> <A HREF='../guide/exceptions.html'>Exceptions</A>), <CODE>flush</CODE> should have been specified to return <CODE>void</CODE> when invoked on a Device. Until the specification is changed, Devices should always return <CODE>true</CODE> when flushed. | |
134 | </P> | |
135 | ||
136 | <!-- Begin Footer --> | |
137 | ||
138 | <HR> | |
139 | ||
140 | <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> | |
141 | <P CLASS="copyright"> | |
142 | 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>) | |
143 | </P> | |
144 | ||
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146 | ||
147 | </BODY> |