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:

string s("123.45");

double amt;
istringstream myString(s);

//istringstream myString("123.45") also works
myString>> amt; // amt contains 123.45

See also

Input Streams