Constructing Input Stream Objects

If you use only the cin object, you do not need to construct an input stream. You must construct an input stream if you use:

• Input File Stream Constructors

• Input String Stream Constructors

Input File Stream Constructors

There are two ways to create an input file stream:

• Use the void argument constructor, then call the open member function:

  ifstream myFile; // On the stack
  myFile.open( "filename" );
  
  ifstream* pmyFile = new ifstream; // On the heap
  pmyFile->open( "filename" );
  

• Specify a filename and mode flags in the constructor invocation, thereby opening the file during the construction process:

  ifstream myFile( "filename" );
  

Input String Stream Constructors

Input string stream constructors require the address of preallocated, preinitialized storage:

char s[] = "123.45";
double amt;
istrstream myString( s );
myString >> amt; // Amt should contain 123.45

See Also

Concepts

Input Streams