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4 | <TITLE>Function Template close</TITLE> |
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9 | <BODY> |
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10 | |
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11 | <!-- Begin Banner --> |
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12 | |
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13 | <H1 CLASS="title">Function Template <CODE>close</CODE></H1> |
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14 | <HR CLASS="banner"> |
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15 | |
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16 | <!-- End Banner --> |
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17 | |
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18 | <DL class="page-index"> |
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19 | <DT><A href="#description">Description</A></DT> |
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20 | <DT><A href="#when">When is <CODE>close</CODE> invoked?</DT> |
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21 | <DT><A href="#headers">Headers</A></DT> |
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22 | <DT><A href="#reference">Reference</A></DT> |
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23 | </DL> |
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24 | |
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25 | <A NAME="description"></A> |
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26 | <H2>Description</H2> |
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27 | |
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28 | <P> |
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29 | The two overloads of the function template <CODE>close</CODE> are invoked automatically by the Iostreams library to indicate to <A HREF="../guide/concepts.html#filter_concepts">Filters</A> and <A HREF="../guide/concepts.html#device_concepts">Devices</A> that a sequence of data is about to end. This gives Filters and Devices an opportunity to free resources or to reset their states in preparation for a new character sequence. Filters and Devices which perform output can use the opportunity to write additional data to the end of a stream. |
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30 | </P> |
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31 | |
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32 | <P>The details regarding when and how <CODE>close</CODE> is invoked are a bit messy:</P> |
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33 | |
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34 | <A NAME="when"></A> |
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35 | <H2>When is <CODE>close</CODE> invoked?</H2> |
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36 | |
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37 | <H4><CODE>stream_buffer</CODE> and <CODE>stream</CODE></H4> |
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38 | |
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39 | <P>When an instance of <CODE>stream_buffer</CODE> or <CODE>stream</CODE> based on a Device <CODE>d</CODE> is closed using member function <CODE>close</CODE>, the following sequence of functions calls is made:<P> |
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40 | <PRE CLASS="broken_ie"> boost::iostreams::close(d, std::ios_base::in); |
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41 | boost::iostreams::close(d, std::ios_base::out);</PRE> |
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42 | <P>The effect, if <CODE>D</CODE> is <A HREF="../concepts/closable.html">Closable</A> and controls a single sequence, is as follows:</P> |
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43 | <PRE CLASS="broken_ie"> d.close();</PRE> |
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44 | <P>If <CODE>D</CODE> is <A HREF="../concepts/closable.html">Closable</A> and controls separate input and output sequences, the effect is as follows:</P> |
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45 | <PRE CLASS="broken_ie"> d.close(std::ios_base::in); |
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46 | d.close(std::ios_base::out);</PRE> |
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47 | |
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48 | <P>(<I>See</I> the semantics of <CODE>close</CODE> for <A HREF="#close_device">Device types</A>, below.) |
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49 | |
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50 | <H4><CODE>filtering_streambuf</CODE> and <CODE>filtering_stream</CODE></H4> |
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51 | |
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52 | <P> |
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53 | A <A HREF="../classes/filtering_streambuf.html"><CODE>filtering_streambuf</CODE></A> or <A HREF="../classes/filtering_stream.html"><CODE>filtering_stream</CODE></A> is considered to be <I>closed</I> if its lifetime ends while its chain is complete or if its terminal Device is removed using <CODE>pop</CODE> or <CODE>reset</CODE>. When this occurs, the following sequence of calls is made, assuming that the underlying sequence of Filters and Devices is <CODE>f<SUB>1</SUB></CODE>, <CODE>f<SUB>1</SUB></CODE>, ..., <CODE>f<SUB>n-1</SUB></CODE>, <CODE>d</CODE> and the corresponding sequence of stream buffers is <CODE>buf<SUB>1</SUB></CODE>, <CODE>buf<SUB>2</SUB></CODE>, ..., <CODE>buf<SUB>n-1</SUB></CODE>, <CODE>buf<SUB>n</SUB></CODE>:<A CLASS='footnote_ref' NAME='note_1_ref' HREF="#note_1"><SUP>[1]</SUP></A> |
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54 | |
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55 | <PRE CLASS="broken_ie"> <SPAN CLASS="keyword">using</SPAN> <SPAN CLASS="keyword">namespace</SPAN> std; |
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56 | |
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57 | <SPAN CLASS="comment">// Close each input sequence, in reverse order:</SPAN> |
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58 | boost::iostreams::close(d,<SPAN STYLE="visibility:hidden"><SUB>n-1</SUB>, buf<SUB>n-1</SUB></SPAN> ios_base::in); |
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59 | boost::iostreams::close(f<SUB>n-1</SUB>, buf<SUB>n</SUB>,<SPAN STYLE="visibility:hidden"><SUB>-1</SUB></SPAN> ios_base::in); |
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60 | boost::iostreams::close(f<SUB>n-2</SUB>, buf<SUB>n-1</SUB>, ios_base::in); |
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61 | <SPAN CLASS="omitted">...</SPAN> |
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62 | boost::iostreams::close(f<SUB>1</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> buf<SUB>2</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> ios_base::in); |
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63 | |
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64 | <SPAN CLASS="comment">// Close each output sequence, in order:</SPAN> |
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65 | boost::iostreams::close(f<SUB>1</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> buf<SUB>2</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> ios_base::out); |
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66 | boost::iostreams::close(f<SUB>2</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> buf<SUB>3</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> ios_base::out); |
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67 | <SPAN CLASS="omitted">...</SPAN> |
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68 | boost::iostreams::close(f<SUB>n-1</SUB>, buf<SUB>n</SUB>,<SPAN STYLE="visibility:hidden"><SUB>n-</SUB></SPAN> ios_base::out); |
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69 | boost::iostreams::close(d,<SPAN STYLE="visibility:hidden"><SUB>n-1</SUB>, buf<SUB>n-1</SUB></SPAN> ios_base::out);</PRE> |
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70 | </P> |
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71 | <P>The effect is that with input streams, the elements of a chain are closed in reverse order; with output streams, they are closed in forward order; and with streams controlling separate input and output sequences, each element receives two closure notifications, the first with argument <CODE>ios_base::in</CODE> and the second with argument <CODE>ios_base::out</CODE>. (<I>See</I> the semantics of <CODE>close</CODE> for <A HREF="#close_filter">Filter</A> and <A HREF="#close_device">Device</A> types, below.) |
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72 | </P> |
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73 | |
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74 | <A NAME="headers"></A> |
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75 | <H2>Headers</H2> |
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76 | |
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77 | <DL> |
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78 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/close.hpp"><CODE><boost/iostreams/close.hpp></CODE></A></DT> |
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79 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/operations.hpp"><CODE><boost/iostreams/operations.hpp></CODE></A></DT> |
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80 | </DL> |
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81 | |
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82 | <A NAME="reference"></A> |
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83 | <H2>Reference</H2> |
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84 | |
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85 | <A NAME="synopsis"></A> |
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86 | <H3>Synopsis</H3> |
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87 | |
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88 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { |
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89 | |
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90 | <SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A CLASS="documented" HREF="#template_params">T</A>> |
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91 | <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#close_device">close</A>(T& t, std::ios_base::openmode which); |
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92 | |
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93 | <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">Device</A>> |
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94 | <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#close_filter">close</A>(T& t, Device& next, std::ios_base::openmode which); |
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95 | |
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96 | } } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE> |
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97 | |
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98 | <A NAME="close_device"></A> |
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99 | <H3>Function Template <CODE>close</CODE> — Device Types</H3> |
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100 | |
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101 | <A NAME="template_params"></A> |
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102 | <H4>Template Parameters</H4> |
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103 | |
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104 | <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> |
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105 | <TR> |
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106 | <TR> |
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107 | <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> |
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108 | <TD>A model of one of the <A HREF="../guide/concepts.html#device_concepts">Device</A> concepts. |
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109 | </TR> |
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110 | </TABLE> |
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111 | |
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112 | <H4>Semantics</H4> |
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113 | |
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114 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T> |
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115 | <SPAN CLASS="keyword">void</SPAN> <A CLASS="documented" HREF="#close_device">close</A>(T& t, std::ios_base::openmode which);</PRE> |
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116 | |
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117 | <P>The semantics of <CODE>close</CODE> for a Device type <CODE>T</CODE> depends on its <A HREF="../guide/traits.html#category">category</A> as follows:</P> |
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118 | |
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119 | <TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4> |
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120 | <TR><TH><CODE>category<T>::type</CODE></TH><TH>semantics</TH></TR> |
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121 | <TR> |
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122 | <TD VALIGN="top">not convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A></TD> |
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123 | <TD>no-op</TD> |
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124 | </TR> |
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125 | <TR> |
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126 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A> and to <A HREF="../guide/modes.html#bidirectional"><CODE>bidirectional</CODE></A></A></TD> |
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127 | <TD>calls <CODE>t.close(which)</CODE></TD> |
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128 | </TR> |
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129 | <TR> |
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130 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A> and to <A HREF="../guide/modes.html#input"><CODE>input</CODE></A> but not to <A HREF="../guide/modes.html#output"><CODE>output</CODE></A></TD> |
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131 | <TD>calls <CODE>t.close()</CODE> if <CODE>(which & ios_base::in) != 0</CODE></TD> |
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132 | </TR> |
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133 | <TR> |
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134 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A> and to <A HREF="../guide/modes.html#input"><CODE>output</CODE></A> but not to <A HREF="../guide/modes.html#bidirectional"><CODE>bidirectional</CODE></A></TD> |
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135 | <TD>calls <CODE>t.close()</CODE> if <CODE>(which & ios_base::out) != 0</CODE></TD> |
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136 | </TR> |
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137 | </TABLE> |
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138 | |
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139 | <P>In short: |
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140 | <UL> |
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141 | <LI CLASS="square">If <CODE>T</CODE> is not <A HREF="../concepts/closable.html">Closable</A>, <CODE>close</CODE> does nothing. |
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142 | <LI CLASS="square">If <CODE>T</CODE> is <A HREF="../concepts/closable.html">Closable</A> and controls two separate sequences, <CODE>close</CODE> delegates to a member function <CODE>close</CODE> taking a single <CODE>openmode</CODE> parameter. |
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143 | <LI CLASS="square">Otherwise, <CODE>close</CODE> delegates to a member function <CODE>close</CODE> taking no parameters, but only if its <CODE>openmode</CODE> parameter is consistent with the mode of <CODE>T</CODE>. |
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144 | </UL> |
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145 | |
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146 | <P>The last condition prevents a Device controlling a single sequence from being closed twice in succession.</P> |
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147 | |
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148 | <A NAME="close_filter"></A> |
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149 | <H3>Function Template <CODE>close</CODE> — Filter Types</H3> |
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150 | |
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151 | <A NAME="template_params"></A> |
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152 | <H4>Template Parameters</H4> |
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153 | |
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154 | <TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2> |
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155 | <TR> |
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156 | <TR> |
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157 | <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> |
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158 | <TD>A model of one of the <A HREF="../guide/concepts.html#filter_concepts">Filter</A> concepts</TD> |
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159 | </TR> |
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160 | <TR> |
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161 | <TD VALIGN="top"><I>Device</I></TD><TD WIDTH="2em" VALIGN="top">-</TD> |
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162 | <TD>A <A HREF="../concepts/blocking.html">Blocking</A> <A HREF="../concepts/device.html">Device</A> whose <A HREF="../guide/modes.html">mode</A> refines that of <CODE>T</CODE>.</TD> |
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163 | </TR> |
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164 | </TABLE> |
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165 | |
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166 | <H4>Semantics</H4> |
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167 | |
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168 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> T, <SPAN CLASS="keyword">typename</SPAN> Device> |
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169 | <SPAN CLASS="keyword">void</SPAN> close(T& t, Device& next, std::ios_base::openmode which);</PRE> |
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170 | |
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171 | <P>The semantics of <CODE>close</CODE> for a Filter type <CODE>T</CODE> depends on its <A HREF="../guide/traits.html#category">category</A> as follows:</P> |
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172 | |
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173 | <TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4> |
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174 | <TR><TH><CODE>category<T>::type</CODE></TH><TH>semantics</TH></TR> |
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175 | <TR> |
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176 | <TD VALIGN="top">not convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A></TD> |
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177 | <TD>no-op</TD> |
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178 | </TR> |
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179 | <TR> |
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180 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A> and to <A HREF="../guide/modes.html#bidirectional"><CODE>bidirectional</CODE></A></A></TD> |
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181 | <TD>calls <CODE>t.close(next, which)</CODE></TD> |
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182 | </TR> |
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183 | <TR> |
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184 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A> and to <A HREF="../guide/modes.html#input"><CODE>input</CODE></A> but not to <A HREF="../guide/modes.html#output"><CODE>output</CODE></A></TD> |
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185 | <TD>calls <CODE>t.close(next)</CODE> if <CODE>(which & ios_base::in) != 0</CODE></TD> |
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186 | </TR> |
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187 | <TR> |
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188 | <TD VALIGN="top">convertible to <A HREF="../guide/traits.html#category_tags"><CODE>closable_tag</CODE></A> and to <A HREF="../guide/modes.html#input"><CODE>output</CODE></A> but not to <A HREF="../guide/modes.html#bidirectional"><CODE>bidirectional</CODE></A></TD> |
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189 | <TD>calls <CODE>t.close(next)</CODE> if <CODE>(which & ios_base::out) != 0</CODE></TD> |
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190 | </TR> |
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191 | </TABLE> |
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192 | |
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193 | <P>In short: |
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194 | <UL> |
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195 | <LI CLASS="square">If <CODE>T</CODE> is not <A HREF="../concepts/closable.html">Closable</A>, <CODE>close</CODE> does nothing. |
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196 | <LI CLASS="square">If <CODE>T</CODE> is <A HREF="../concepts/closable.html">Closable</A> and controls two separate sequences, <CODE>close</CODE> delegates to a member function <CODE>close</CODE> taking <CODE>openmode</CODE> and stream buffer parameters. |
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197 | <LI CLASS="square">Otherwise, <CODE>close</CODE> delegates to a member function <CODE>close</CODE> taking a single stream buffer parameter, but only if its <CODE>openmode</CODE> parameter is consistent with the mode of <CODE>T</CODE>. |
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198 | </UL> |
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199 | |
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200 | <P>The last condition prevents a Filter controlling a single sequence from being closed twice in succession.</P> |
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201 | |
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202 | <!-- End Footnotes --> |
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203 | |
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204 | <HR> |
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205 | |
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206 | <P> |
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207 | <A CLASS='footnote_ref' NAME='note_1' HREF="#note_1_ref"><SUP>[1]</SUP></A>This behavior can be disabled in the case of <CODE>pop</CODE> by calling member function <CODE>set_auto_close</CODE> with the argument <CODE>false</CODE>. See, e.g., <A HREF="../classes/filtering_stream.html#set_auto_close"><CODE>filtering_stream::set_auto_close</CODE></A>. |
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208 | </P> |
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209 | |
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210 | <!-- Begin Footnotes --> |
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211 | |
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212 | <!-- Begin Footer --> |
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213 | |
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214 | <HR> |
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215 | <P CLASS="copyright">Revised |
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216 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
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217 | 20 May, 2004 |
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218 | <!--webbot bot="Timestamp" endspan i-checksum="38504" --> |
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219 | </P> |
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220 | |
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221 | <P CLASS="copyright">© Copyright <A HREF="http://www.kangaroologic.com" TARGET="_top">Jonathan Turkanis</A>, 2004</P> |
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222 | <P CLASS="copyright"> |
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223 | 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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224 | </P> |
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225 | |
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226 | <!-- End Footer --> |
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227 | |
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228 | </BODY> |
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