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    <H1 CLASS="title">I/O Traits and Categories</H1>
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<DL class="page-index">
  <DT><A href="#overview">Overview</A></DT>
  <DT><A href="#headers">Headers</A></DT>
  <DT><A href="#char_type_of_ref">Class template <CODE>char_type_of</CODE></A></DT>
  <DT><A href="#int_type_of_ref">Class template <CODE>int_type_of</CODE></A></DT>
  <DT><A href="#category_ref">Class template <CODE>category_of</CODE></A></DT>
  <DT><A href="#category_tags">Category Tags</A></DT>
  </DT>
</DL>

<HR>

<A NAME="overview"></A>
<H2>Overview</H2>

<P>
    The header <A CLASS="header" href="../../../../boost/iostreams/categories.hpp"><CODE>&lt;boost/iostreams/categories.hpp&gt;</CODE></A> contains <A href="#category_tags">category tags</A> for classifying models of the various <A href="concepts.html#filter_concepts">Filter</A> and <A href="concepts.html#device_concepts">Device</A> concepts. The header <A CLASS="header" href="../../../../boost/iostreams/traits.hpp"><CODE>&lt;boost/iostreams/traits.hpp&gt;</CODE></A> contains the definitions of the metafunctions <A HREF="#char_type_of_ref"><CODE>char_type_of</CODE></A> and <A HREF="#category_ref"><CODE>category</CODE></A>, used to associate two fundamental types with each model of one the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts:
</P>

<A NAME="char_type"></A>
<H4>Character Type</H4>

<P>The type of characters which a Filter or Device reads or writes.</P>

<A NAME="category"></A>
<H4>Category</H4>

<P>
    A tag structure which the Iostreams library relies on to determine which operations a Filter or Device supports. It indicates, for a given type <CODE>T</CODE>:
</P>
<UL>
    <LI CLASS="square">whether <CODE>T</CODE> is a <A href="concepts.html#filter_concepts">Filter</A> or a <A href="concepts.html#device_concepts">Device</A>
    <LI CLASS="square">the <A href="modes.html">mode</A> of <CODE>T</CODE>
    <LI CLASS="square">any <A href="concepts.html#optional_behavior">optional_behavior</A> <CODE>T</CODE> implements
</UL>
<P>
   Its function is similar to the <CODE>iterator_category</CODE> member of <CODE>std::iterator_traits</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref" HREF="#note_1"><SUP>[1]</SUP></A> Types which serve as categories are called <A HREF="#category_tags">category tags</A>.
</P>

<A NAME="headers"></A>
<H2>Headers</H2>

<DL class="page-index">
  <DT><A CLASS="header" href="../../../../boost/iostreams/categories.hpp"><CODE>&lt;boost/iostreams/categories.hpp&gt;</CODE></A></DT>
  <DT><A CLASS="header" href="../../../../boost/iostreams/traits.hpp"><CODE>&lt;boost/iostreams/traits.hpp&gt;</CODE></A></DT>
</DL>

<A NAME="char_type_of_ref"></A>
<H2>Class Template <CODE>char_type_of</CODE></H2>

<H4>Description</H4>

<P><A HREF="http://www.boost.org/libs/mpl/doc/refmanual/metafunction.html" TARGET="_top">Metafunction</A> associating a <A HREF="#char_type">character type</A> to each <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> type. Although <CODE>char_type_of</CODE> is designed to be specialized for new Filter and Device types, the default implementation should be suitable for most purposes.

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A HREF="#char_type_template_params" CLASS="documented">T</A>&gt;
<SPAN CLASS="keyword">struct</SPAN> <A CLASS="documented" HREF="#char_type_template_params">char_type_of</A> {
    <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> <A HREF="#char_type_of_type" CLASS="documented">type</A>;
};

} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>

<A NAME="char_type_template_params"></A>
<H4>Template parameters</H4>

<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
    <TR>
        <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>A model of one of the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts</TD>
    </TR>
</TABLE>

<A NAME="char_type_of_type"></A>
<H4><CODE>io_traits::type</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> char_type;</PRE>

<P>The value of the nested type <CODE>type</CODE> depends on the template parameter <CODE>T</CODE> as follows:</P>

<TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
<TR><TH><CODE>T</CODE></TH><TH><CODE>char_type</CODE></TH></TR>
    <TR>
        <TD VALIGN="top">Sepcialization of <CODE>std::back_insert_iterator</CODE></TD>
        <TD>The <CODE>value_type</CODE> of the iterator's <CODE>container_type</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">All other types</TD>
        <TD><CODE>T::char_type</CODE></TD>
    </TR>
</TABLE>

<A NAME="int_type_of_ref"></A>
<H2>Class Template <CODE>int_type_of</CODE></H2>

<H4>Description</H4>

<P><A HREF="http://www.boost.org/libs/mpl/doc/refmanual/metafunction.html" TARGET="_top">Metafunction</A> associating an integral type to each <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> type. Although <CODE>int_type_of</CODE> is designed to be specialized for new Filter and Device types, the default implementation should be suitable for most purposes.

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A HREF="#int_type_template_params" CLASS="documented">T</A>&gt;
<SPAN CLASS="keyword">struct</SPAN> <A CLASS="documented" HREF="#int_type_template_params">int_type_of</A> {
    <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> <A HREF="#int_type_of_type" CLASS="documented">type</A>;
};

} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>

<A NAME="int_type_template_params"></A>
<H4>Template parameters</H4>

<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
    <TR>
        <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>A model of one of the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts</TD>
    </TR>
</TABLE>

<A NAME="int_type_of_type"></A>
<H4><CODE>io_traits::type</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> char_type;</PRE>

<P>Equal to <CODE>std::char_traits&lt;char_type&gt;::int_type</CODE>, where <CODE>char_type</CODE> is <A HREF="#char_type_of_ref"><CODE>char_type_of&lt;T&gt;::type</CODE></A>.

<A NAME="category_ref"></A>
<H2>Class Template <CODE>category_of</CODE></H2>

<H4>Description</H4>

<P><A HREF="http://www.boost.org/libs/mpl/doc/refmanual/metafunction.html" TARGET="_top">Metafunction</A> associating a <A HREF="#category_tags">category tag</A> to each <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> type. Although <CODE>category</CODE> is designed to be specialized for new Filter and Device types, the default implementation should be suitable for most purposes.

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS="keyword">template</SPAN>&lt;<SPAN CLASS="keyword">typename</SPAN> <A HREF="#category_template_params" CLASS="documented">T</A>&gt;
<SPAN CLASS="keyword">struct</SPAN> <A CLASS="documented" HREF="#category_template_params">category_of</A> {
    <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> <A HREF="#category_type" CLASS="documented">type</A>;
};

} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>

<A NAME="category_template_params"></A>
<H4>Template parameters</H4>

<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
    <TR>
        <TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>A model of one of the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts</TD>
    </TR>
</TABLE>

<A NAME="category_type"></A>
<H4><CODE>category::type</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> type;</PRE>

<P>The value of the nested type <CODE>type</CODE> depends on the template parameter <CODE>T</CODE> as follows:</P>

<TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
    <TR><TH><CODE>T</CODE></TH><TH><CODE>category</CODE></TH></TR>
    <TR>
        <TD VALIGN="top">Specialization of <CODE>std::basic_iostream</CODE>, or derived from such a specialization</TD>
        <TD><CODE>iostream_tag</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">Specialization of <CODE>std::basic_istream</CODE>, or derived from such a specialization</TD>
        <TD><CODE>istream_tag</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">Specialization of <CODE>std::basic_ostream</CODE>, or derived from such a specialization</TD>
        <TD><CODE>ostream_tag</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">Specialization of <CODE>std::basic_streambuf</CODE>, or derived from such a specialization</TD>
        <TD><CODE>streambuf_tag</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">Specialization of <CODE>std::back_insert_iterator</CODE>, or derived from such a specialization</TD>
        <TD><CODE>insert_iterator_tag</CODE></TD>
    </TR>
    <TR>
        <TD VALIGN="top">All other types</TD>
        <TD><CODE>T::category</CODE></TD>
    </TR>
</TABLE>

<P>For more information, see <A CLASS="header" href="../../../../boost/iostreams/traits.hpp"><CODE>&lt;boost/iostreams/traits.hpp&gt;</CODE></A>.</P>

<A NAME="category_tags"></A>
<H2>Category Tags</H2>

<P>
    In addition to the various <A href="modes.html#mode_tags">mode tags</A>, the header <A CLASS="header" href="../../../../boost/iostreams/categories.hpp"><CODE>&lt;boost/iostreams/categories.hpp&gt;</CODE></A> provides the category tags shown in the following table. To produce a new category tag which combines several existing tags, simply define a <CODE>struct</CODE> extending the existing tags. <I>E.g.</I>, 
    <PRE CLASS="broken_ie">    <SPAN CLASS="keyword">struct</SPAN> category
        : seekable,
          filter_tag, 
          localizable_tag 
        { };</PRE>
    This defines a category tag representing <A href="modes.html#seekable">Seekable</A>, <A href="../concepts/localizable.html">Localizable</A> <A href="../concepts/filter.html">Filters</A>.
</P>


<TABLE STYLE="margin-left:2em;margin-bottom:2em" BORDER="1" CELLPADDING="6">
    <TR><TH>Tag</TH><TH>Description</TH></TR>
    <TR>
        <TD VALIGN="top"><CODE>filter_tag</CODE></TD>
        <TD>Indicates that a type models <A href="../concepts/filter.html">Filter</A></TD>
    </TR>
    <TR>
        <TD VALIGN="top"><CODE>device_tag</CODE></TD>
        <TD>Indicates that a type models <A href="../concepts/device.html">Device</A></TD>
    </TR>
    <TR>
        <TD VALIGN="top">
            <CODE>closable_tag</CODE><BR><CODE>localizable_tag</CODE><BR>
            <CODE>direct_tag</CODE><BR><CODE>peekable_tag</CODE><BR>
            <CODE>multichar_tag</CODE>
        </TD>
        <TD>
            Used to indicate <A href="concepts.html#optional_behavior">optional behavior</A> implemented by a Filter or Device type
        </TD>
    </TR>
    <TR>
        <TD VALIGN="top">
            <CODE>source_tag</CODE><BR>
            <CODE>sink_tag</CODE><BR>
            <CODE>bidirectional_device_tag</CODE><BR>
            <CODE>seekable_device_tag</CODE><BR>
            <CODE>input_filter_tag</CODE><BR>
            <CODE>output_filter_tag</CODE><BR>
            <CODE>bidirectional_filter_tag</CODE><BR>
            <CODE>seekable_filter_tag</CODE><BR>
            <CODE>multichar_input_filter_tag</CODE><BR>
            <CODE>multichar_output_filter_tag</CODE><BR>
            <CODE>multichar_bidirectional_filter_tag</CODE><BR>
            <CODE>multichar_seekable_filter_tag</CODE>
        </TD>
        <TD>
            Convenience tags for defining models of the various <A href="../concepts/filter.html">Filter</A> and <A href="../concepts/device.html">Device</A> refinements
        </TD>
    </TR>
    <TR>
        <TD VALIGN="top">
            <CODE>istream_tag</CODE><BR>
            <CODE>ostream_tag</CODE><BR>
            <CODE>iostream_tag</CODE><BR>
            <CODE>streambuf_tag</CODE>
        </TD>
        <TD>
            Used internally to distinguish standard stream and stream buffer types
        </TD>
    </TR>
    <TR>
        <TD VALIGN="top"><CODE>insert_iterator_tag</CODE></TD>
        <TD>Used internally to distinguish specialization of <CODE>std::back_insert_iterator</CODE></TD>
    </TR>
</TABLE>

<!-- Begin Footnotes -->

<HR>

<P>
    <A CLASS="footnote_ref" NAME="note_1" HREF="#note_1_ref"><SUP>[1]</SUP></A><A CLASS="bib_ref" href="../bibliography.html#iso">[I<SPAN STYLE="font-size:80%">SO</SPAN>]</A> 24.3.1. <I>See</I> <A HREF="http://www.boost.org/more/generic_programming.html#tag_dispatching" TARGET="_top">Tag Dispatching</A> for a discussion.
</P>

<!-- End Footnotes -->

<!-- Begin Footer -->

<HR>

<P CLASS="copyright">&copy; Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>&copy; Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a></P>
<P CLASS="copyright"> 
    Use modification and distribution are subject to the Boost Software License Version 1.0. (See accompanying file <A href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
</P>

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Commit	Line	Data
7c673cae FG	1	<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
	2	<HTML>
	3	<HEAD>
	4	<TITLE>I/O Traits and Categories</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">I/O Traits and Categories</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="#char_type_of_ref">Class template <CODE>char_type_of</CODE></A></DT>
	21	<DT><A href="#int_type_of_ref">Class template <CODE>int_type_of</CODE></A></DT>
	22	<DT><A href="#category_ref">Class template <CODE>category_of</CODE></A></DT>
	23	<DT><A href="#category_tags">Category Tags</A></DT>
	24	</DT>
	25	</DL>
	26
	27	<HR>
	28
	29	<A NAME="overview"></A>
	30	<H2>Overview</H2>
	31
	32	<P>
	33	The header <A CLASS="header" href="../../../../boost/iostreams/categories.hpp"><CODE><boost/iostreams/categories.hpp></CODE></A> contains <A href="#category_tags">category tags</A> for classifying models of the various <A href="concepts.html#filter_concepts">Filter</A> and <A href="concepts.html#device_concepts">Device</A> concepts. The header <A CLASS="header" href="../../../../boost/iostreams/traits.hpp"><CODE><boost/iostreams/traits.hpp></CODE></A> contains the definitions of the metafunctions <A HREF="#char_type_of_ref"><CODE>char_type_of</CODE></A> and <A HREF="#category_ref"><CODE>category</CODE></A>, used to associate two fundamental types with each model of one the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts:
	34	</P>
	35
	36	<A NAME="char_type"></A>
	37	<H4>Character Type</H4>
	38
	39	<P>The type of characters which a Filter or Device reads or writes.</P>
	40
	41	<A NAME="category"></A>
	42	<H4>Category</H4>
	43
	44	<P>
	45	A tag structure which the Iostreams library relies on to determine which operations a Filter or Device supports. It indicates, for a given type <CODE>T</CODE>:
	46	</P>
	47	<UL>
	48	<LI CLASS="square">whether <CODE>T</CODE> is a <A href="concepts.html#filter_concepts">Filter</A> or a <A href="concepts.html#device_concepts">Device</A>
	49	<LI CLASS="square">the <A href="modes.html">mode</A> of <CODE>T</CODE>
	50	<LI CLASS="square">any <A href="concepts.html#optional_behavior">optional_behavior</A> <CODE>T</CODE> implements
	51	</UL>
	52	<P>
	53	Its function is similar to the <CODE>iterator_category</CODE> member of <CODE>std::iterator_traits</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref" HREF="#note_1"><SUP>[1]</SUP></A> Types which serve as categories are called <A HREF="#category_tags">category tags</A>.
	54	</P>
	55
	56	<A NAME="headers"></A>
	57	<H2>Headers</H2>
	58
	59	<DL class="page-index">
	60	<DT><A CLASS="header" href="../../../../boost/iostreams/categories.hpp"><CODE><boost/iostreams/categories.hpp></CODE></A></DT>
	61	<DT><A CLASS="header" href="../../../../boost/iostreams/traits.hpp"><CODE><boost/iostreams/traits.hpp></CODE></A></DT>
	62	</DL>
	63
	64	<A NAME="char_type_of_ref"></A>
65	<H2>Class Template <CODE>char_type_of</CODE></H2>
66
67	<H4>Description</H4>
68
69	<P><A HREF="http://www.boost.org/libs/mpl/doc/refmanual/metafunction.html" TARGET="_top">Metafunction</A> associating a <A HREF="#char_type">character type</A> to each <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> type. Although <CODE>char_type_of</CODE> is designed to be specialized for new Filter and Device types, the default implementation should be suitable for most purposes.
70
71	<H4>Synopsis</H4>
72
73	<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
74
75	<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A HREF="#char_type_template_params" CLASS="documented">T</A>>
76	<SPAN CLASS="keyword">struct</SPAN> <A CLASS="documented" HREF="#char_type_template_params">char_type_of</A> {
77	<SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> <A HREF="#char_type_of_type" CLASS="documented">type</A>;
78	};
79
80	} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
81
82	<A NAME="char_type_template_params"></A>
83	<H4>Template parameters</H4>
84
85	<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
86	<TR>
87	<TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
88	<TD>A model of one of the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts</TD>
89	</TR>
90	</TABLE>
91
92	<A NAME="char_type_of_type"></A>
93	<H4><CODE>io_traits::type</CODE></H4>
94
95	<PRE CLASS="broken_ie"> <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> char_type;</PRE>
96
97	<P>The value of the nested type <CODE>type</CODE> depends on the template parameter <CODE>T</CODE> as follows:</P>
98
99	<TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
100	<TR><TH><CODE>T</CODE></TH><TH><CODE>char_type</CODE></TH></TR>
101	<TR>
102	<TD VALIGN="top">Sepcialization of <CODE>std::back_insert_iterator</CODE></TD>
103	<TD>The <CODE>value_type</CODE> of the iterator's <CODE>container_type</CODE></TD>
104	</TR>
105	<TR>
106	<TD VALIGN="top">All other types</TD>
107	<TD><CODE>T::char_type</CODE></TD>
108	</TR>
109	</TABLE>
110
111	<A NAME="int_type_of_ref"></A>
112	<H2>Class Template <CODE>int_type_of</CODE></H2>
113
114	<H4>Description</H4>
115
116	<P><A HREF="http://www.boost.org/libs/mpl/doc/refmanual/metafunction.html" TARGET="_top">Metafunction</A> associating an integral type to each <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> type. Although <CODE>int_type_of</CODE> is designed to be specialized for new Filter and Device types, the default implementation should be suitable for most purposes.
117
118	<H4>Synopsis</H4>
119
120	<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
121
122	<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A HREF="#int_type_template_params" CLASS="documented">T</A>>
123	<SPAN CLASS="keyword">struct</SPAN> <A CLASS="documented" HREF="#int_type_template_params">int_type_of</A> {
124	<SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> <A HREF="#int_type_of_type" CLASS="documented">type</A>;
125	};
126
127	} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
128
129	<A NAME="int_type_template_params"></A>
130	<H4>Template parameters</H4>
131
132	<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
133	<TR>
134	<TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
135	<TD>A model of one of the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts</TD>
136	</TR>
137	</TABLE>
138
139	<A NAME="int_type_of_type"></A>
140	<H4><CODE>io_traits::type</CODE></H4>
141
142	<PRE CLASS="broken_ie"> <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> char_type;</PRE>
143
144	<P>Equal to <CODE>std::char_traits<char_type>::int_type</CODE>, where <CODE>char_type</CODE> is <A HREF="#char_type_of_ref"><CODE>char_type_of<T>::type</CODE></A>.
145
146	<A NAME="category_ref"></A>
147	<H2>Class Template <CODE>category_of</CODE></H2>
148
149	<H4>Description</H4>
150
151	<P><A HREF="http://www.boost.org/libs/mpl/doc/refmanual/metafunction.html" TARGET="_top">Metafunction</A> associating a <A HREF="#category_tags">category tag</A> to each <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> type. Although <CODE>category</CODE> is designed to be specialized for new Filter and Device types, the default implementation should be suitable for most purposes.
152
153	<H4>Synopsis</H4>
154
155	<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
156
157	<SPAN CLASS="keyword">template</SPAN><<SPAN CLASS="keyword">typename</SPAN> <A HREF="#category_template_params" CLASS="documented">T</A>>
158	<SPAN CLASS="keyword">struct</SPAN> <A CLASS="documented" HREF="#category_template_params">category_of</A> {
159	<SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> <A HREF="#category_type" CLASS="documented">type</A>;
160	};
161
162	} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>
163
164	<A NAME="category_template_params"></A>
165	<H4>Template parameters</H4>
166
167	<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
168	<TR>
169	<TD VALIGN="top"><I>T</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
170	<TD>A model of one of the <A href="concepts.html#filter_concepts">Filter</A> or <A href="concepts.html#device_concepts">Device</A> concepts</TD>
171	</TR>
172	</TABLE>
173
174	<A NAME="category_type"></A>
175	<H4><CODE>category::type</CODE></H4>
176
177	<PRE CLASS="broken_ie"> <SPAN CLASS="keyword">typedef</SPAN> <SPAN CLASS="omitted">see below</SPAN> type;</PRE>
178
179	<P>The value of the nested type <CODE>type</CODE> depends on the template parameter <CODE>T</CODE> as follows:</P>
180
181	<TABLE STYLE="margin-left:2em" BORDER=1 CELLPADDING=4>
182	<TR><TH><CODE>T</CODE></TH><TH><CODE>category</CODE></TH></TR>
183	<TR>
184	<TD VALIGN="top">Specialization of <CODE>std::basic_iostream</CODE>, or derived from such a specialization</TD>
185	<TD><CODE>iostream_tag</CODE></TD>
186	</TR>
187	<TR>
188	<TD VALIGN="top">Specialization of <CODE>std::basic_istream</CODE>, or derived from such a specialization</TD>
189	<TD><CODE>istream_tag</CODE></TD>
190	</TR>
191	<TR>
192	<TD VALIGN="top">Specialization of <CODE>std::basic_ostream</CODE>, or derived from such a specialization</TD>
193	<TD><CODE>ostream_tag</CODE></TD>
194	</TR>
195	<TR>
196	<TD VALIGN="top">Specialization of <CODE>std::basic_streambuf</CODE>, or derived from such a specialization</TD>
197	<TD><CODE>streambuf_tag</CODE></TD>
198	</TR>
199	<TR>
200	<TD VALIGN="top">Specialization of <CODE>std::back_insert_iterator</CODE>, or derived from such a specialization</TD>
201	<TD><CODE>insert_iterator_tag</CODE></TD>
202	</TR>
203	<TR>
204	<TD VALIGN="top">All other types</TD>
205	<TD><CODE>T::category</CODE></TD>
206	</TR>
207	</TABLE>
208
209	<P>For more information, see <A CLASS="header" href="../../../../boost/iostreams/traits.hpp"><CODE><boost/iostreams/traits.hpp></CODE></A>.</P>
210
211	<A NAME="category_tags"></A>
212	<H2>Category Tags</H2>
213
214	<P>
215	In addition to the various <A href="modes.html#mode_tags">mode tags</A>, the header <A CLASS="header" href="../../../../boost/iostreams/categories.hpp"><CODE><boost/iostreams/categories.hpp></CODE></A> provides the category tags shown in the following table. To produce a new category tag which combines several existing tags, simply define a <CODE>struct</CODE> extending the existing tags. <I>E.g.</I>,
216	<PRE CLASS="broken_ie"> <SPAN CLASS="keyword">struct</SPAN> category
217	: seekable,
218	filter_tag,
219	localizable_tag
220	{ };</PRE>
221	This defines a category tag representing <A href="modes.html#seekable">Seekable</A>, <A href="../concepts/localizable.html">Localizable</A> <A href="../concepts/filter.html">Filters</A>.
222	</P>
223
224
225	<TABLE STYLE="margin-left:2em;margin-bottom:2em" BORDER="1" CELLPADDING="6">
226	<TR><TH>Tag</TH><TH>Description</TH></TR>
227	<TR>
228	<TD VALIGN="top"><CODE>filter_tag</CODE></TD>
229	<TD>Indicates that a type models <A href="../concepts/filter.html">Filter</A></TD>
230	</TR>
231	<TR>
232	<TD VALIGN="top"><CODE>device_tag</CODE></TD>
233	<TD>Indicates that a type models <A href="../concepts/device.html">Device</A></TD>
234	</TR>
235	<TR>
236	<TD VALIGN="top">
237	<CODE>closable_tag</CODE><BR><CODE>localizable_tag</CODE><BR>
238	<CODE>direct_tag</CODE><BR><CODE>peekable_tag</CODE><BR>
239	<CODE>multichar_tag</CODE>
240	</TD>
241	<TD>
242	Used to indicate <A href="concepts.html#optional_behavior">optional behavior</A> implemented by a Filter or Device type
243	</TD>
244	</TR>
245	<TR>
246	<TD VALIGN="top">
247	<CODE>source_tag</CODE><BR>
248	<CODE>sink_tag</CODE><BR>
249	<CODE>bidirectional_device_tag</CODE><BR>
250	<CODE>seekable_device_tag</CODE><BR>
251	<CODE>input_filter_tag</CODE><BR>
252	<CODE>output_filter_tag</CODE><BR>
253	<CODE>bidirectional_filter_tag</CODE><BR>
254	<CODE>seekable_filter_tag</CODE><BR>
255	<CODE>multichar_input_filter_tag</CODE><BR>
256	<CODE>multichar_output_filter_tag</CODE><BR>
257	<CODE>multichar_bidirectional_filter_tag</CODE><BR>
258	<CODE>multichar_seekable_filter_tag</CODE>
259	</TD>
260	<TD>
261	Convenience tags for defining models of the various <A href="../concepts/filter.html">Filter</A> and <A href="../concepts/device.html">Device</A> refinements
262	</TD>
263	</TR>
264	<TR>
265	<TD VALIGN="top">
266	<CODE>istream_tag</CODE><BR>
267	<CODE>ostream_tag</CODE><BR>
268	<CODE>iostream_tag</CODE><BR>
269	<CODE>streambuf_tag</CODE>
270	</TD>
271	<TD>
272	Used internally to distinguish standard stream and stream buffer types
273	</TD>
274	</TR>
275	<TR>
276	<TD VALIGN="top"><CODE>insert_iterator_tag</CODE></TD>
277	<TD>Used internally to distinguish specialization of <CODE>std::back_insert_iterator</CODE></TD>
278	</TR>
279	</TABLE>
280
281	<!-- Begin Footnotes -->
282
283	<HR>
284
285	<P>
286	<A CLASS="footnote_ref" NAME="note_1" HREF="#note_1_ref"><SUP>[1]</SUP></A><A CLASS="bib_ref" href="../bibliography.html#iso">[I<SPAN STYLE="font-size:80%">SO</SPAN>]</A> 24.3.1. <I>See</I> <A HREF="http://www.boost.org/more/generic_programming.html#tag_dispatching" TARGET="_top">Tag Dispatching</A> for a discussion.
287	</P>
288
289	<!-- End Footnotes -->
290
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292
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294
295	<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>
296	<P CLASS="copyright">
297	Use modification and distribution are subject to the Boost Software License Version 1.0. (See accompanying file <A href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
298	</P>
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