Performance difference between accessing via reference or pointer

Question

Is there a performance difference between this code :

struct foo   example;

my_function(&example);

void         my_function(struct foo *example);

And this code :

struct foo   example;

my_function(example);

void         my_function(struct foo &example);

I think that both approaches are different, but is there any performance difference between them ?

Second snippet is invalid in C. There is no pass by reference in C. — haccks, Jun 05 '15 at 22:51
http://stackoverflow.com/questions/6732706/c-passing-arguments-by-reference-and-pointer — Varaquilex, Jun 05 '15 at 22:52
You tagged your question with C, but C doesn't have references. Did you mean C++? Apart from that there shouldn't be any difference performance wise. — Daniel Jour, Jun 05 '15 at 22:55
A reference is a pointer which hides the pointer semantics. As other stated already, C has no references, only (explicit) pointers, so the question is nonsense — too honest for this site, Jun 05 '15 at 23:27

score 1 · Answer 1 · answered Jun 05 '15 at 23:34

The code you posted is C++, not C, as C lacks references.

That said, a reference type in C++ is hardly different from a pointer except that it cannot point to different pointees (cannot store different addresses) after initialization. It practically is a pointer with the pointer semantics to get from pointer to pointee hidden away.

With references, you can get some added safety in cases where the reference should always point to something valid. For example, you can't assign a null to a reference. So from a C++ standpoint, many often encourage using references whenever possible because the fact that it has more constraints and narrows the options might mean fewer ways to misuse it.

From a performance standpoint, in a very theoretical realm, an optimizing compiler may possibly use the fact that a reference cannot change addresses once assigned to its benefit. In practice, most optimizing compilers aren't so dumb as to require this help from the programmer and many have testified that optimizing compilers emit the same assembly regardless of whether you use references or pointers.

So the practical answer to your question is generally no, there is no performance difference.

Performance difference between accessing via reference or pointer

1 Answers1