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| <TITLE>basic_ifstream</TITLE> |
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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> <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 <fstream> |
| |
| namespace std { |
| template<class charT, class traits = char_traits<charT> > |
| 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<class charT, class traits = char_traits<charT> > |
| class basic_ifstream |
| : public basic_istream<charT, traits> |
| { |
| 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<char_type, traits_type> *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 <SAMP>char</SAMP>:</P> |
| <P><SAMP>typedef basic_ifstream<char> 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<wchar_t> 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<char_type, traits_type>(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<char_type, traits_type>(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<char_type, traits_type>(rdbuf())</SAMP>. The constructor then calls <SAMP>rdbuf()->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 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<char_type, traits_type>(rdbuf())</SAMP>.The constructor then calls <SAMP>rdbuf()->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 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<char_type, traits_type>(rdbuf ())</SAMP>. The constructor then calls <SAMP>rdbuf()->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 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()->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()->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()->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()->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 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()->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 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()->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 B</A> for a complete list of extensions of this implementation. |
| </B><HR></BLOCKQUOTE> |
| |
| <A NAME="idx105"></A><PRE>basic_filebuf<charT,traits>* |
| <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 <fstream> // for fstream |
| #include <iomanip> // for setw |
| #include <iostream> // 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 << ntbs << 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 << std::endl; |
| else |
| std::cout << c; |
| } |
| |
| std::cout << 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 << 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 >> buf) { |
| std::cout.width (10); |
| std::cout << buf << std::endl; |
| } |
| |
| std::cout << std::endl; |
| |
| // clear flags, last in >> buf set fail bit |
| // because of a newline at end of string |
| in.clear (); |
| |
| // output the base info before each integer |
| out << std::showbase; |
| |
| std::ostream::pos_type pos= out.tellp (); |
| |
| const long l = 10; |
| |
| // output l in hex with a field with of 10 |
| out << std::hex << std::setw (10) << l << std::endl; |
| |
| // output l in oct with a field with of 10 |
| out << std::oct << std::setw (10) << l << std::endl; |
| |
| // output l in dec with a field with of 10 |
| out << std::dec << std::setw (10) << l << std::endl; |
| |
| // move back to the beginning of the file |
| in.seekg (0); |
| |
| // output the entire file |
| std::cout << in.rdbuf () << 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 >> a >> b >> d; |
| |
| // output 3 times 10 |
| std::cout << a << std::endl << b << std::endl << d |
| << std::endl; |
| } |
| catch (std::ios::failure e) { |
| std::cout << 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> |
| <HR> |
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