Question

foo();

(*foo)();

(&foo)();

What exactly is the difference between these function calls (assuming foo() is defined somewhere)? and are there any situations where one might be used over another?

Also, why don’t &foo() and *foo() work?

Answer 1

There is no difference between the actual calls themselves (rather, they will all do the same thing depending on how foo() is declared)

All function calls in C and C++ take place via a function-pointer expression which appears before the function call parentheses. Implicit address-of of non-pointer types takes place if necessary.

Here’s an ideone demonstrating the behavior in C++.

The reason &foo() and *foo() don’t work is that the function call operator () takes precedence over * and &. So they might work, depending on what you were doing with the return value. &foo() would take the return value’s address, and *foo() would dereference it. Under some circumstances, either of these operations, or both, might be legal. Consider a function returning a reference-to-pointer type.

Part of this answer taken from R..’s comment.