ifstream a_file;

ifstream a_file ( "filename" );

 
#include <fstream>
#include <iostream>

using namespace std;

int main()
{
  char str[10];

  //Creates an instance of ofstream, and opens example.txt
  ofstream a_file ( "example.txt" );
  // Outputs to example.txt through a_file
  a_file<<"This text will now be inside of example.txt";
  // Close the file stream explicitly
  a_file.close();
  //Opens for reading the file
  ifstream b_file ( "example.txt" );
  //Reads one string from the file
  b_file>> str;
  //Should output 'this'
  cout<< str <<"\n";
  // b_file is closed implicitly here
}

 
ios::app   -- Append to the file
ios::ate   -- Set the current position to the end
ios::trunc -- Delete everything in the file

 
ofstream a_file ( "test.txt", ios::app );

 
ifstream a_file ( "example.txt" );

if ( !a_file.is_open() ) {
  // The file could not be opened
}
else {
  // Safely use the file stream
}