Calling an Overloaded Operator Function Directly

Ordinarily, we “call” an overloaded operator function indirectly by using the operator on arguments of the appropriate type. However, we can also call an overloaded operator function directly in the same way that we call an ordinary function. We name the function and pass an appropriate number of arguments of the appropriate type:

// equivalent calls to a nonmember operator function
data1 + data2;           // normal expression
operator+(data1, data2); // equivalent function call

These calls are equivalent: Both call the nonmember function operator+, passing data1 as the first argument and data2 as the second.

We call a member operator function explicitly in the same way that we call any other member function. We name an object (or pointer) on which to run the function and use the dot (or arrow) operator to fetch the function we wish to call:

data1 += data2;             // expression-based ''call''
data1.operator+=(data2);    // equivalent call to a member operator function

Each of these statements calls the member function operator+=, binding this to the address of data1 and passing data2 as an argument.