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<A HREF="basic-fstream.html"><IMG SRC="images/bprev.gif" WIDTH=20 HEIGHT=21 ALT="Previous file" BORDER=O></A><A HREF="noframes.html"><IMG SRC="images/btop.gif" WIDTH=56 HEIGHT=21 ALT="Top of Document" BORDER=O></A><A HREF="booktoc.html"><IMG SRC="images/btoc.gif" WIDTH=56 HEIGHT=21 ALT="Contents" BORDER=O></A><A HREF="tindex.html"><IMG SRC="images/bindex.gif" WIDTH=56 HEIGHT=21 ALT="Index page" BORDER=O></A><A HREF="basic-ios.html"><IMG SRC="images/bnext.gif" WIDTH=25 HEIGHT=21 ALT="Next file" BORDER=O></A><DIV CLASS="DOCUMENTNAME"><B>Apache C++ Standard Library Reference Guide</B></DIV>
<H2>basic_ifstream</H2>
<P><B>Library:</B>&nbsp;&nbsp;<A HREF="2-11.html">Input/output</A></P>
<PRE><HR><B><I>basic_ifstream</I></B> <IMG SRC="images/inherits.gif"> <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> <IMG SRC="images/inherits.gif"> <B><I><A HREF="basic-ios.html">basic_ios</A></I></B> <IMG SRC="images/inherits.gif"> <B><I><A HREF="ios-base.html">ios_base</A></I></B><HR></PRE>
<UL>
<LI><A HREF="#sec1">Local Index</A></LI>
<LI><A HREF="#sec2">Summary</A></LI>
<LI><A HREF="#sec3">Synopsis</A></LI>
<LI><A HREF="#sec4">Description</A></LI>
<LI><A HREF="#sec5">Interface</A></LI>
<LI><A HREF="#sec6">Member Types</A></LI>
<LI><A HREF="#sec7">Nonmember Types</A></LI>
<LI><A HREF="#sec8">Constructors</A></LI>
<LI><A HREF="#sec9">Member Functions</A></LI>
<LI><A HREF="#sec10">Example</A></LI>
<LI><A HREF="#sec11">See Also</A></LI>
<LI><A HREF="#sec12">Standards Conformance</A></LI>
</UL>
<A NAME="sec1"><H3>Local Index</H3></A>
<H4>Members</H4>
<UL><TABLE CELLPADDING=3>
<TR><TD VALIGN=top>
<A HREF="#idx94">basic_ifstream()</A><BR>
<A HREF="#idx87">char_type</A><BR>
<A HREF="#idx99">close()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx88">int_type</A><BR>
<A HREF="#idx100">is_open()</A><BR>
<A HREF="#idx89">off_type</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx101">open()</A><BR>
<A HREF="#idx90">pos_type</A><BR>
<A HREF="#idx105">rdbuf()</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx91">traits_type</A><BR>
</TD></TR>
</TABLE></UL>
<H4>Non-Members</H4>
<UL><TABLE CELLPADDING=3>
<TR><TD VALIGN=top>
<A HREF="#idx92">ifstream</A><BR>
</TD>
<TD VALIGN=top><A HREF="#idx93">wifstream</A><BR>
</TD>
<TD VALIGN=top></TD></TR>
</TABLE></UL>
<A NAME="sec2"><H3>Summary</H3></A>
<P>Class that supports reading from named files or other devices associated with a file descriptor</P>
<A NAME="sec3"><H3>Synopsis</H3></A>
<PRE>#include &lt;fstream&gt;
namespace std {
template&lt;class charT, class traits = char_traits&lt;charT&gt; &gt;
class basic_ifstream;
}
</PRE>
<A NAME="sec4"><H3>Description</H3></A>
<P>The class template <B><I>basic_ifstream</I></B> supports reading from named files or other devices associated with a file descriptor. It uses a <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> object to control the associated sequences. It inherits from <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> and can therefore use all the formatted and unformatted input functions.</P>
<A NAME="sec5"><H3>Interface</H3></A>
<UL><PRE>namespace std {
template&lt;class charT, class traits = char_traits&lt;charT&gt; &gt;
class basic_ifstream
: public basic_istream&lt;charT, traits&gt;
{
public:
typedef traits traits_type;
typedef charT char_type;
typedef typename traits::int_type int_type;
typedef typename traits::pos_type pos_type;
typedef typename traits::off_type off_type;
basic_ifstream();
explicit basic_ifstream(const char*,
ios_base::openmode = ios_base::in);
// extensions:
explicit basic_ifstream(const char*,
ios_base::openmode, long);
explicit basic_ifstream(int, char_type* = 0,
streamsize = /* default size */);
explicit basic_ifstream(FILE*, char_type* = 0,
streamsize = /* default size */);
basic_filebuf&lt;char_type, traits_type&gt; *rdbuf() const;
bool is_open() const;
void open(const char*, ios_base::openmode mode =
ios_base::in);
// extensions:
void open(const char*, ios_base::openmode, long);
void open(int, char_type* = 0,
streamsize = /* default size */);
void open(FILE*, char_type* = 0,
streamsize = /* default size */);
void close();
};
</PRE></UL>
<A NAME="sec6"><H3>Member Types</H3></A>
<A NAME="idx87"></A><PRE><B>char_type</B></PRE>
<UL>
<P>The type <SAMP>char_type</SAMP> is a synonym for the template parameter <SAMP>charT</SAMP>.</P>
</UL>
<A NAME="idx88"></A><PRE><B>int_type</B></PRE>
<UL>
<P>The type <SAMP>int_type</SAMP> is a synonym of type <SAMP>traits::in_type</SAMP>.</P>
</UL>
<A NAME="idx89"></A><PRE><B>off_type</B></PRE>
<UL>
<P>The type <SAMP>off_type</SAMP> is a synonym of type <SAMP>traits::off_type</SAMP>.</P>
</UL>
<A NAME="idx90"></A><PRE><B>pos_type</B></PRE>
<UL>
<P>The type <SAMP>pos_type</SAMP> is a synonym of type <SAMP>traits::pos_type</SAMP>.</P>
</UL>
<A NAME="idx91"></A><PRE><B>traits_type</B></PRE>
<UL>
<P>The type <SAMP>traits_type</SAMP> is a synonym for the template parameter <SAMP>traits</SAMP>.</P>
</UL>
<A NAME="sec7"><H3>Nonmember Types</H3></A>
<A NAME="idx92"></A><PRE><B>ifstream</B></PRE>
<UL>
<P>The type <SAMP>ifstream</SAMP> is a specialization of class template <B><I>basic_ifstream</I></B> on type&nbsp;<SAMP>char</SAMP>:</P>
<P><SAMP>typedef basic_ifstream&lt;char&gt; ifstream;</SAMP></P>
</UL>
<A NAME="idx93"></A><PRE><B>wifstream</B></PRE>
<UL>
<P>The type <SAMP>wifstream</SAMP> is a specialization of class template <B><I>basic_ifstream</I></B> on type <SAMP>wchar_t</SAMP>:</P>
<P><SAMP>typedef basic_ifstream&lt;wchar_t&gt; wifstream;</SAMP></P>
</UL>
<A NAME="sec8"><H3>Constructors</H3></A>
<A NAME="idx94"></A><PRE><B>basic_ifstream</B>();</PRE>
<UL>
<P>Constructs an object of class <B><I>basic_ifstream</I></B>, initializing the base class <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> with the associated file buffer. This buffer is initialized by calling the <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> constructor <SAMP>basic_filebuf&lt;char_type, traits_type&gt;(rdbuf())</SAMP>. After construction, a file can be attached to the <B><I>basic_ifstream</I></B> object by using the <SAMP>open()</SAMP> member function.</P>
</UL>
<A NAME="idx95"></A><PRE><B>basic_ifstream</B>(const char* s,
ios_base::openmode mode = ios_base::in); </PRE>
<UL>
<P>Constructs an object of class <B><I>basic_ifstream</I></B>, initializing the base class <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> with the associated file buffer. This buffer is initialized by calling the <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> constructor <SAMP>basic_filebuf&lt;char_type, traits_type&gt;(rdbuf())</SAMP>. The constructor then calls <SAMP>open(s,mode) </SAMP>in order to attach the file, whose name is pointed to by <SAMP>s</SAMP>, to the <B><I>basic_ifstream</I></B> object. </P>
</UL>
<A NAME="idx96"></A><PRE><B>basic_ifstream</B>(const char* s, ios_base::openmode mode,
long protection = 0666);</PRE>
<UL>
<P>Constructs an object of class <B><I>basic_ifstream</I></B>, initializing the base class <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> with the associated file buffer. This buffer is initialized by calling the <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> constructor <SAMP>basic_filebuf&lt;char_type, traits_type&gt;(rdbuf())</SAMP>. The constructor then calls <SAMP>rdbuf()-&gt;open (s, mode, protection)</SAMP> in order to attach the file, whose name is pointed to by <SAMP>s</SAMP>, to the <B><I>basic_ifstream</I></B> object. The third argument, <SAMP>protection</SAMP>, holds file permissions. It determines the read/write/execute file permissions under UNIX, but is more limited elsewhere.</P>
</UL>
<BLOCKQUOTE><HR><B>
NOTE -- This function is not part of the C++ Standard, but is included here as a convenience extension. See <A HREF="B.html">Appendix&nbsp;B</A> for a complete list of extensions of this implementation.
</B><HR></BLOCKQUOTE>
<A NAME="idx97"></A><PRE><B>basic_ifstream</B>(int fd, char_type *buf, streamsize n); </PRE>
<UL>
<P>Constructs an object of class <B><I>basic_ifstream</I></B>, initializing the base class <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> with the associated file buffer. This buffer is initialized by calling the <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> constructor <SAMP>basic_filebuf&lt;char_type, traits_type&gt;(rdbuf())</SAMP>.The constructor then calls <SAMP>rdbuf()-&gt;open (fd, buf, n)</SAMP> in order to attach the file descriptor, <SAMP>fd</SAMP>, to the <B><I>basic_ifstream</I></B> object. If the function fails, it sets <SAMP>ios_base::failbit</SAMP>. </P>
</UL>
<BLOCKQUOTE><HR><B>
NOTE -- This function is not part of the C++ Standard, but is included here as an extension in order to manipulate pipes, sockets, or other UNIX devices that can be accessed through file descriptors. See <A HREF="B.html">Appendix&nbsp;B</A> for a complete list of extensions of this implementation.
</B><HR></BLOCKQUOTE>
<A NAME="idx98"></A><PRE><B>basic_ifstream</B>(FILE *fp, char_type* buf, streamsize n); </PRE>
<UL>
<P>Constructs an object of class <B><I>basic_ifstream</I></B>, initializing the base class <B><I><A HREF="basic-istream.html">basic_istream</A></I></B> with the associated file buffer. This buffer is initialized by calling the <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> constructor <SAMP>basic_filebuf&lt;char_type, traits_type&gt;(rdbuf ())</SAMP>. The constructor then calls <SAMP>rdbuf()-&gt;open (fp, buf, n)</SAMP> in order to attach the file pointer, <SAMP>fp,</SAMP> to the <B><I>basic_ifstream</I></B> object. If the function fails, it sets <SAMP>ios_base::failbit</SAMP>.</P>
</UL>
<BLOCKQUOTE><HR><B>
NOTE -- This function is not part of the C++ Standard, but is provided here as a convenience extension. See <A HREF="B.html">Appendix&nbsp;B</A> for a complete list of extensions of this implementation.
</B><HR></BLOCKQUOTE>
<A NAME="sec9"><H3>Member Functions</H3></A>
<A NAME="idx99"></A><PRE>void
<B>close</B>();</PRE>
<UL>
<P>Calls <SAMP>rdbuf()-&gt;close()</SAMP>; if it fails, calls the <B><I><A HREF="basic-ios.html">basic_ios</A></I></B> member function <SAMP>setstate(failbit)</SAMP>.</P>
</UL>
<A NAME="idx100"></A><PRE>bool
<B>is_open</B>() const;</PRE>
<UL>
<P>Returns <SAMP>rdbuf()-&gt;is_open()</SAMP>.</P>
</UL>
<A NAME="idx101"></A><PRE>void
<B>open</B>(const char* s,ios_base::openmode = ios_base::in);</PRE>
<UL>
<P>Calls <SAMP>rdbuf()-&gt;open(s, mode)</SAMP> to open the file. If the call fails, calls the <B><I><A HREF="basic-ios.html">basic_ios</A></I></B> member function <SAMP>setstate(failbit)</SAMP>.</P>
</UL>
<A NAME="idx102"></A><PRE>void
<B>open</B>(const char* s, ios_base::openmode, long protection);</PRE>
<UL>
<P>Calls <SAMP>rdbuf()-&gt;open (s, mode, protection)</SAMP> to open the file. If the call fails, calls the <B><I><A HREF="basic-ios.html">basic_ios</A></I></B> member function <SAMP>setstate(failbit)</SAMP>. The third argument, <SAMP>protection</SAMP>, holds file permissions. <SAMP>protection</SAMP> determines the read/write/execute file permissions under UNIX. It is more limited under DOS, since files are always readable and do not have special execute permission.</P>
</UL>
<BLOCKQUOTE><HR><B>
NOTE -- The third argument, protection, is not part of the C++ Standard, but is provided here as an extension. See <A HREF="B.html">Appendix&nbsp;B</A> for a complete list of extensions of this implementation to the Standard.
</B><HR></BLOCKQUOTE>
<A NAME="idx103"></A><PRE>void
<B>open</B>(int fd, char_type *buf = 0,
streamsize n = /* default size */);</PRE>
<UL>
<P>Calls <SAMP>rdbuf()-&gt;open (fd, buf, n)</SAMP> to open the file. If the call fails, calls the <B><I><A HREF="basic-ios.html">basic_ios</A></I></B> member function <SAMP>setstate(failbit)</SAMP>. </P>
</UL>
<BLOCKQUOTE><HR><B>
NOTE -- This function is not part of the C++ Standard, but is provided here as an extension. See <A HREF="B.html">Appendix&nbsp;B</A> for a complete list of extensions of this implementation.
</B><HR></BLOCKQUOTE>
<A NAME="idx104"></A><PRE>void
<B>open</B>(FILE *fp, char_type *buf = 0,
streamsize n = /* default size */);</PRE>
<UL>
<P>Calls <SAMP>rdbuf()-&gt;open (fp, buf, n)</SAMP> to open the file. If that call fails, calls <SAMP>setstate (ios::failbit)</SAMP>.</P>
</UL>
<BLOCKQUOTE><HR><B>
NOTE -- This function is not part of the C++ Standard, but is provided here as an extension. See <A HREF="B.html">Appendix&nbsp;B</A> for a complete list of extensions of this implementation.
</B><HR></BLOCKQUOTE>
<A NAME="idx105"></A><PRE>basic_filebuf&lt;charT,traits&gt;*
<B>rdbuf</B>() const; </PRE>
<UL>
<P>Returns a pointer to the <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B> associated with the stream.</P>
</UL>
<A NAME="sec10"><H3>Example</H3></A>
<UL><PRE>//
// ifstream.cpp
//
#include &lt;fstream&gt; // for fstream
#include &lt;iomanip&gt; // for setw
#include &lt;iostream&gt; // for cout, endl
int main ( )
{
const char *ntbs = "Le minot passait la piece a frotter.";
char c;
try {
// create a read/write file-stream object
std::ifstream in ("ifstream.results.out",
std::ios::in | std::ios::out |
std::ios::trunc);
if (!in.is_open ())
throw (std::ios::failure ("open error"));
// associate the ostream object's buffer with
// the ifstream object
std::ostream out (in.rdbuf ());
// output ntbs in out
out &lt;&lt; ntbs &lt;&lt; std::endl;
// seek to the beginning of the file
in.seekg (0);
// output each space-separated word on a separate line
while (in.get (c)) {
if (std::isspace (c, in.getloc ()))
std::cout &lt;&lt; std::endl;
else
std::cout &lt;&lt; c;
}
std::cout &lt;&lt; std::endl;
// clear stream state, failbit | eofbit set by last call
// to get ()
in.clear ();
// move back to the beginning of the file
in.seekg (0);
char buf [40];
// guard against buffer overflow
in.width (sizeof buf);
// set right justification
std::cout &lt;&lt; std::right;
// does the same thing as the previous code
// output each word on a separate line in a field
// of width 10
while (in &gt;&gt; buf) {
std::cout.width (10);
std::cout &lt;&lt; buf &lt;&lt; std::endl;
}
std::cout &lt;&lt; std::endl;
// clear flags, last in &gt;&gt; buf set fail bit
// because of a newline at end of string
in.clear ();
// output the base info before each integer
out &lt;&lt; std::showbase;
std::ostream::pos_type pos= out.tellp ();
const long l = 10;
// output l in hex with a field with of 10
out &lt;&lt; std::hex &lt;&lt; std::setw (10) &lt;&lt; l &lt;&lt; std::endl;
// output l in oct with a field with of 10
out &lt;&lt; std::oct &lt;&lt; std::setw (10) &lt;&lt; l &lt;&lt; std::endl;
// output l in dec with a field with of 10
out &lt;&lt; std::dec &lt;&lt; std::setw (10) &lt;&lt; l &lt;&lt; std::endl;
// move back to the beginning of the file
in.seekg (0);
// output the entire file
std::cout &lt;&lt; in.rdbuf () &lt;&lt; std::endl;
// clear the flags
in.clear ();
// seek the input sequence to pos
in.seekg (pos);
int a, b, d;
in.unsetf (std::ios::basefield);
// read the previous outputted integer
in &gt;&gt; a &gt;&gt; b &gt;&gt; d;
// output 3 times 10
std::cout &lt;&lt; a &lt;&lt; std::endl &lt;&lt; b &lt;&lt; std::endl &lt;&lt; d
&lt;&lt; std::endl;
}
catch (std::ios::failure e) {
std::cout &lt;&lt; e.what ();
}
return 0;
}
Program Output:
</PRE></UL>
<UL><PRE>Le
minot
passait
la
piece
a
frotter.
Le
minot
passait
la
piece
a
frotter.
Le minot passait la piece a frotter.
0xa
012
10
10
10
10
</PRE></UL>
<A NAME="sec11"><H3>See Also</H3></A>
<P><B><I><A HREF="char-traits.html">char_traits</A></I></B>, <B><I><A HREF="ios-base.html">ios_base</A></I></B>, <B><I><A HREF="basic-ios.html">basic_ios</A></I></B>, <B><I><A HREF="basic-filebuf.html">basic_filebuf</A></I></B>, <B><I><A HREF="basic-ofstream.html">basic_ofstream</A></I></B>, <B><I><A HREF="basic-fstream.html">basic_fstream</A></I></B></P>
<A NAME="sec12"><H3>Standards Conformance</H3></A>
<P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 27.8.1.5</I></P>
<BR>
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