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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<TITLE>File Descriptor Devices</TITLE>
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<LINK REL="stylesheet" HREF="../../../../boost.css">
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<STYLE> H3 CODE { font-size: 110% } </STYLE>
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<!-- Begin Banner -->
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<H1 CLASS="title">File Descriptors</H1>
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<DL class="page-index">
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<DT><A href="#overview">Overview</A></DT>
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<DT><A href="#acknowledgments">Acknowledments</A></DT>
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<DT><A href="#installation">Installation</A></DT>
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<DT><A href="#headers">Headers</A></DT>
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<DT><A href="#reference">Reference</A>
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<UL>
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<LI CLASS="square"><A href="#file_descriptor_source">Class <CODE>file_descriptor_source</CODE></A></LI>
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<LI CLASS="square"><A href="#file_descriptor_sink">Class <CODE>file_descriptor_sink</CODE></A></LI>
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<LI CLASS="square"><A href="#file_descriptor">Class <CODE>file_descriptor</CODE></A></LI>
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</DT>
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</DL>
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<A NAME="overview">
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<H2>Overview</H2>
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<P>
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The classes <CODE>file_descriptor_source</CODE>, <CODE>file_descriptor_sink</CODE> and <CODE>file_descriptor</CODE> provide file access via operating system file handles or file descriptors. These <A HREF="../guide/concepts.html#device_concepts">Devices</A> behave much like the <A HREF="file.html">File Wrappers</A> <CODE>basic_file_source</CODE>, <CODE>basic_file_sink</CODE> and <CODE>basic_file</CODE>, with the following important differences:
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<UL>
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<LI CLASS="square">A file descriptor Device may be constructed from a file descriptor which is already open.
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<LI CLASS="square">The only <A HREF="../guide/buffering.html">buffering</A> is provded by the Boost Iostreams library.
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<LI CLASS="square">There is no automatic line-ending conversion.
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<LI CLASS="square">Wide-character streams are not supported.
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</UL>
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<P>
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When a file descriptor Device is copied, the result represents the same underlying file descriptor. The underlying file descriptor is <I>not</I> duplicated.
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</P>
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<P>
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The classes <CODE>file_descriptor</CODE> supports 64-bit seek offsets whenever they are supported by the underlying operating system or runtime library. Currently, file descriptor Devices may not work corectly with file descriptors opened in non-blocking mode.
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Line-ending conversion can be provided, if desired, using the class <A HREF="newline_filter.html"><CODE>newline_filter</CODE></A>. Wide-character versions of the file descriptor Devices may be defined as follows, using the template <A HREF="code_converter.html"><CODE>code_converter</CODE></A>:
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<PRE CLASS="broken_ie"> <SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/code_converter.hpp"><SPAN CLASS="literal"><boost/iostreams/code_converter.hpp></SPAN></A>
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<SPAN CLASS="preprocessor">#include</SPAN> <A CLASS="header" HREF="../../../../boost/iostreams/device/file_descriptor.hpp"><SPAN CLASS="literal"><boost/iostreams/maped_file.hpp></SPAN></A>
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<SPAN CLASS='keyword'>typedef</SPAN> code_converter<file_descriptor_source> wfile_descriptor_source;
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<SPAN CLASS='keyword'>typedef</SPAN> code_converter<file_descriptor_sink> wfile_descriptor_sink;</PRE>
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</P>
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<A NAME="acknowledgments">
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<H2>Acknowledgments</H2>
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<P>
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The file descriptor Devices are based on work of Nicolai Josuttis (<A CLASS="bib_ref" HREF="../bibliography.html#josuttis1">[Josuttis1]</A> <I>pp.</I> 672-3 and <A CLASS="bib_ref" HREF="../bibliography.html#josuttis2">[Josuttis2]</A>).
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</P>
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<A NAME="installation">
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<H2>Installation</H2>
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<P>
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The file descriptor Devices depends on the source file <A CLASS="header" HREF="../../src/file_descriptor.cpp"><CODE><libs/iostreams/src/file_descriptor.cpp></CODE></A>, which makes use of Windows or POSIX headers depending on the user's operating system. For installation instructions see <A HREF="../installation.html">Installation</A>.
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</P>
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<A NAME="headers">
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<H2>Headers</H2>
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<DL class="page-index">
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<DT><A CLASS="header" HREF="../../../../boost/iostreams/device/file_descriptor.hpp"><CODE><boost/iostreams/device/file_descriptor.hpp></CODE></A></DT>
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</DL>
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<A NAME="reference">
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<H2>Reference</H2>
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<A NAME="file_descriptor_source">
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<H3>Class <CODE>file_descriptor_source</CODE></H3>
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<H4>Description</H4>
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<P>Model of <A HREF="../concepts/source.html">Source</A> providing read-only access to a file through an operating system file descriptor.</P>
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<H4>Synopsis</H4>
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<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
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<SPAN CLASS="keyword">class</SPAN> file_descriptor_source {
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<SPAN CLASS="keyword">public</SPAN>:
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<SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='keyword'>char</SPAN> char_type;
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<SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN> category;
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file_descriptor_source( <SPAN CLASS="keyword">const</SPAN> std::string& pathname,
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std::ios_base::open_mode mode =
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std::ios_base::in );
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file_descriptor_source( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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<SPAN CLASS='comment'>// Windows-only</SPAN>
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file_descriptor_source( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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};
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} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>
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<A NAME="file_descriptor_source_ctor"></A>
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<H4><CODE>file_descriptor_source::file_descriptor_source</CODE></H4>
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<A NAME="file_descriptor_source_ctor"></A>
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<PRE CLASS="broken_ie"> file_descriptor_source( <SPAN CLASS="keyword">const</SPAN> std::string& pathname,
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std::ios_base::open_mode mode =
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std::ios_base::in );
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file_descriptor_source( <SPAN CLASS="keyword">int </SPAN>fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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<SPAN CLASS='comment'>// Windows-only</SPAN>
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file_descriptor_source( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>
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<P>
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The first member constructs a <CODE>file_descriptor_source</CODE> to access the file with the given pathname. The parameter <CODE>mode</CODE> has the same interpretation as <CODE>(mode | std::ios_base::in)</CODE> in <CODE>std::basic_filebuf::open</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref" HREF="#note_1"><SUP>[1]</SUP></A>
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</P>
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<P>
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The second member constructs a <CODE>file_descriptor_source</CODE> to access the file with the given operating system or runtime-library file descriptor. If the second argument is <CODE>true</CODE>, the file descriptor is closed when the <CODE>file_descriptor_source</CODE> being constructed — or one of its copies — is closed.
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</P>
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<P>
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The third member is the same as the second, except that it accepts a Windows file handle instead of a file descriptor. If the second argument is <CODE>true</CODE>, the file descriptor is closed when the <CODE>file_descriptor_source</CODE> being constructed — or one of its copies — is closed.
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</P>
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<A NAME="file_descriptor_sink">
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<H3>Class <CODE>file_descriptor_sink</CODE></H3>
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<H4>Description</H4>
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<P>Model of <A HREF="../concepts/sink.html">Sink</A> providing write-only access to a file through an operating system file descriptor.
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<H4>Synopsis</H4>
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<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
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<SPAN CLASS="keyword">class</SPAN> file_descriptor_sink {
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<SPAN CLASS="keyword">public</SPAN>:
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<SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='keyword'>char</SPAN> char_type;
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<SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN> category;
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file_descriptor_sink( <SPAN CLASS="keyword">const</SPAN> std::string& pathname,
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std::ios_base::open_mode mode =
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std::ios_base::out );
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file_descriptor_sink( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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<SPAN CLASS='comment'>// Windows-only</SPAN>
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file_descriptor_sink( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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};
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} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>
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<A NAME="file_descriptor_sink_ctor"></A>
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<H4><CODE>file_descriptor_sink::file_descriptor_sink</CODE></H4>
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<PRE CLASS="broken_ie"> file_descriptor_sink( <SPAN CLASS="keyword">const</SPAN> std::string& pathname,
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std::ios_base::open_mode mode =
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std::ios_base::out );
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file_descriptor_sink( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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<SPAN CLASS='comment'>// Windows-only</SPAN>
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file_descriptor_sink( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>
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<P>
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The first member constructs a <CODE>file_descriptor_sink</CODE> to access the file with the given pathname. The parameter <CODE>mode</CODE> has the same interpretation as <CODE>(mode | std::ios_base::out)</CODE> in <CODE>std::basic_filebuf::open</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref" HREF="#note_1"><SUP>[1]</SUP></A>
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</P>
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<P>
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The second member constructs a <CODE>file_descriptor_sink</CODE> to access the file with the given operating system or runtime-library file descriptor. If the second argument is <CODE>true</CODE>, the file descriptor is closed when the new <CODE>file_descriptor_sink</CODE> — or one of its copies — is closed.
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</P>
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<P>
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The third member is the same as the second, except that it accepts a Windows file handle instead of a file descriptor. If the second argument is <CODE>true</CODE>, the file descriptor is closed when the new <CODE>file_descriptor_sink</CODE> — or one of its copies — is closed.
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</P>
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<A NAME="file_descriptor">
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<H3>Class <CODE>file_descriptor</CODE></H3>
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<H4>Description</H4>
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<P>Model of <A HREF="../concepts/seekable_device.html">SeekableDevice</A> providing read-write access to a file through an operating system file descriptor.
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<H4>Synopsis</H4>
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<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {
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<SPAN CLASS="keyword">class</SPAN> file_descriptor {
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<SPAN CLASS="keyword">public</SPAN>:
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<SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='keyword'>char</SPAN> char_type;
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<SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN> category;
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file_descriptor( <SPAN CLASS="keyword">const</SPAN> std::string& pathname,
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std::ios_base::open_mode mode =
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std::ios_base::in | std::ios_base::out );
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file_descriptor( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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<SPAN CLASS='comment'>// Windows-only</SPAN>
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file_descriptor( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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};
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} } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE>
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<A NAME="file_descriptor_constructor"></A>
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<H4><CODE>file_descriptor::file_descriptor</CODE></H4>
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<PRE CLASS="broken_ie"> file_descriptor( <SPAN CLASS="keyword">const</SPAN> std::string& pathname,
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std::ios_base::open_mode mode =
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std::ios_base::in | std::ios_base::out );
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file_descriptor( <SPAN CLASS="keyword">int</SPAN> fd, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );
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<SPAN CLASS='comment'>// Windows-only</SPAN>
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file_descriptor( HANDLE hFile, <SPAN CLASS="keyword">bool</SPAN> close_on_exit = <SPAN CLASS="keyword">false</SPAN> );</PRE>
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<P>
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The first member constructs a <CODE>file_descriptor</CODE> to access the file with the given pathname. The parameter <CODE>mode</CODE> has the same interpretation as in <CODE>std::basic_filebuf::open</CODE>.<A CLASS="footnote_ref" NAME="note_1_ref" HREF="#note_1"><SUP>[1]</SUP></A>
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</P>
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<P>
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The second member constructs a <CODE>file_descriptor</CODE> to access the file with the given operating system or runtime-library file descriptor. If the second argument is <CODE>true</CODE>, the file descriptor is closed when the new <CODE>file_descriptor</CODE> — or one of its copies — is closed.
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</P>
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<P>
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The third member is the same as the second, except that it accepts a Windows file handle instead of a file descriptor. If the second argument is <CODE>true</CODE>, the file descriptor is closed when the new <CODE>file_descriptor</CODE> — or one of its copies — is closed.
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</P>
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<!-- Begin Footnotes -->
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<HR>
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<P>
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<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>, Table 92.
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</P>
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<!-- End Footnotes -->
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<!-- Begin Footer -->
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<HR>
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<P CLASS="copyright">Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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20 May, 2004
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<!--webbot bot="Timestamp" endspan i-checksum="38504" -->
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</P>
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<P CLASS="copyright">© Copyright Jonathan Turkanis, 2004</P>
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<P CLASS="copyright">
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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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