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    <H1 CLASS="title">Flushable</H1>
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<H2>Description</H2>

<P>
    A Flushable Sink or OutputFilter provides a means for the user to request that all buffered characters be sent downstream.
</P>

<H2>Refinement of</H2>

<A NAME="types"></A>
<H2>Associated Types</H2>

<P>Same as <A HREF="filter.html#types">Filter</A> or <A HREF="device.html#types">Device</A>, with the following additional requirement:</P>

<TABLE CELLPADDING="5" BORDER="1">
    <TR><TD>Category</TD><TD>A type convertible to <A HREF="../guide/traits.html#category_tags"><CODE>flushable_tag</CODE></A></TD></TR>
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<H2>Notation</H2>

<TABLE CELLPADDING="2">
    <TR><TD><CODE>F</CODE></TD><TD>-</TD><TD>A type which is a model of Flushable</TD></TR>
    <TR><TD><CODE>D</CODE></TD><TD>-</TD><TD>A type which is a model of <A HREF="device.html">Sink</A>, with the same character type as <CODE>F</CODE></TD></TR>
    <TR><TD><CODE>f</CODE></TD><TD>-</TD><TD>Object of type <CODE>F</CODE></TD></TR>
    <TR><TD><CODE>d</CODE></TD><TD>-</TD><TD>Object of type <CODE>D</CODE></TD></TR>
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<H2>Valid Expressions / Semantics</H2>

<TABLE CELLPADDING="5" BORDER="1">
    <TR><TH>Expression</TH><TH>Expression Type</TH><TH>Precondition</TH><TH>Semantics</TH></TR>
    <TR>
        <TD>
            <PRE CLASS="plain_code"><CODE><A HREF="../functions/flush.html#flush_device">boost::iostreams::flush</A>(f)</CODE></PRE>
        </TD>
        <TD><CODE>bool</CODE></TD>
        <TD>Category convertible to <A HREF="../guide/traits.html#category_tags"><CODE>device_tag</CODE></A></TD>
        <TD>
            Attempts to send all buffered characters downstream, returning <CODE>true</CODE> unless an error occurs.<A CLASS='footnote_ref' NAME='note_1_ref' HREF='#note_1'><SUP>[1]</SUP></A>
        </TD>
    </TR>
    <TR>
        <TD>
            <PRE CLASS="plain_code"><CODE><A HREF="../functions/flush.html#flush_filter">boost::iostreams::flush</A>(f, d)</CODE></PRE>
        </TD>
        <TD><CODE>bool</CODE></TD>
        <TD>Category convertible to <A HREF="../guide/traits.html#category_tags"><CODE>filter_tag</CODE></A></TD>
        <TD>
            <P>
                Attempts to write all buffered characters to d, returning <CODE>true</CODE> if all buffered characters were written.
            </P>
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    </TR>
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<H2>Exceptions</H2>

<P>
    Errors which occur during the execution of <A CLASS="code" HREF="../functions/flush.html"><CODE>flush</CODE></A> are be indicated by throwing exceptions. Such exceptions are caught and ignored if they occur during the execution of stream or stream buffer destructor.
</P>

<H2>Models</H2>

<P>Several of the Filters and Devices provided by the Iostreams library are Flushable, but this is an implementation detail.</P>

<HR>

<P>
    <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.
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    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>)
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