What are the benefits to passing integral types by const ref

Question

The question: Is there benefit to passing an integral type by const reference as opposed to simply by value.

ie.

void foo(const int& n); // case #1
<         


        

Answer 1

It depends on the compiler, but I'd expect that any reasonable optimizer would give you the same results either way.

I tested with gcc, and the results were indeed the same. here's the code I tested:

inline int foo(const int& n) {
  return n * 2;
}

int bar(int x) {
  int y = foo(x);
  return y;
}

(with and without const & on foo's n parameter)

I then compiled with gcc 4.0.1 with the following command line:

g++ -O3 -S -o foo.s foo.cc

The outputs of the two compiles were identical.