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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

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
    ifstream* pmyFile = new ifstream; // On the heap
  • 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