=====open=====
Syntax:

<code>
    #include <fstream>
    void fstream::open(const char *filename, openmode mode = default_mode);
</code>
The function open() is used with file streams. It opens filename and associates
it with the current stream. The mode parameter defaults to
ios::in for ifstream, ios::out for ofstream, and ios::in|ios::out for fstream.
If open() fails, the stream is put into a non-good state which may be checked. For example:

<code>
   ifstream inputStream;
   inputStream.open("file.txt");

   if( !inputStream ) {
     cerr << "Error opening input stream" << endl;
   }
   // or
   if ( inputStream ) {
     // use inputStream
   }
</code>

Related Topics: [[IO/Constructors]], [[close]], [[io_flags#mode_flags|C++ I/O Mode Flags]]