22.5.2 Assigning Function Pointers

Assuming we have declared the variable binary_op as in the previous section, giving it a value requires a suitable function to use. So let’s define a function suitable for the variable to point to. Here’s one:

double
double_add (double a, double b)
{
  return a+b;
}

Now we can give it a value:

binary_op = double_add;

The target type of the function pointer must be upward compatible with the type of the function (see Compatible Types).

There is no need for ‘&’ in front of double_add. Using a function name such as double_add as an expression automatically converts it to the function’s address, with the appropriate function pointer type. However, it is ok to use ‘&’ if you feel that is clearer:

binary_op = &double_add;