Construct an object and optionally open a file.
  Constructs an object of class ifstream. This implies the initialization of the associated filebuf object and the call to its base class' constructor with the filebuf object as constructor parameter.
  Additionally, in case the second constructor syntax is used, the stream's file is associated with a physical file as if a call to member open with the same parameters was made.

Parameters.

filename

String containing the name of the file to be opened.

mode

Flags describing the requested i/o mode for the file. This is an object of type ios_base::openmode, it generally consist of a combination of the following flags (member constants):

bit	effect
app	(append) Seek to the end of the stream before each output operation.
ate	(at end) Seek to the end of the stream when opening.
binary	Consider stream as binary rather than text.
in	Allow input operations on a stream.
out	Allow output operations on a stream.
trunc	(truncate) Truncate file to zero when opening.

Return Value.
  none

Example.

// using ifstream constructors.
#include <iostream>
#include <fstream>
using namespace std;

int main () {

  ifstream infile ("test.txt");

  while (infile.good())
    cout << (char) infile.get();

  infile.close();

  return 0;
}

Basic template member declaration ( basic_ifstream<charT,traits> ):

basic_ifstream(); explicit basic_ifstream ( const char * filename, openmode mode = in );

See also.
  open
  ifstream class