Pass reference to output location vs using return

Question

Which is better for performance when calling a function that provides a simple datatype -- having it fill in a memory location (passed by pointer) or having it return the simple data?

I've oversimplified the example returning a static value of 5 here, but assume the lookup/functionality that determines the return value would be dynamic in real life...

Conventional logic would tell me the first approach is quicker since we are operating by reference instead of having to return a copy as in the 2nd approach... But, I'd like others' opinions.

Thanks

void func(int *a) { *a = 5; }

or...

int func() { return 5; }

Answer 1

In general, if your function acts like a function (that is, returning a single logical value), then it's probably best to use int func(). Even if the return value is a complex C++ object, there's a common optimisation called Return Value Optimisation that avoids unnecessary object copying and makes the two forms roughly equivalent in runtime performance.