Question

Hey there,
I wonder if it’s worth passing primitive single values like int, float, double or char by pointer? Probably it’s not worth!? But if you would simply pass everything by pointer, is this making the program slower?
Should you always just pass arrays as pointer?
Thanks!

Answer 1

I wonder if it’s worth passing primitive single values like int, float, double or char by pointer?

What are you trying to accomplish? Do you want to be able to write to the passed in value? Or do you just need to use it? If you want to write to it, the idiomatic way is to pass by reference. If you don’t need to write to it, you’re best avoiding any risk that you’ll write to it accidentally and pass by value. Pass by value will make a copy of the variable for local use. (as an aside, if you don’t want to make a copy AND want some level of safety, you can pass by const reference)

But if you would simply pass everything by pointer, is this making the program slower?

Difficult to say. Depends on a lot of things. In both pass by value and pass by reference (or pointer) your making a new primitive type. In pass by value, you’re making a copy. In pass by reference/pointer you’re passing an address to the original. In the latter case, however, you’re requiring an extra fetch of memory that may or may not be cached. Its very difficult to say 100% without measuring it.

That all being said, I doubt the difference is even noticeable. The compiler may be able to optimize out the copy in many pass-by-value cases, as indicated in this article. (thanks Space C0wb0y).

Should you always just pass arrays as pointer?

From this.

In C++ it is not possible to pass a complete block of memory by value as a parameter to a function, but we are allowed to pass its address.

To pass an array:

 int foo(int bar[], unsigned int length)
 {
       // do stuff with bar but don't go past length
 }

I’d recommended avoiding arrays and using std::vector which has more easily understood copy semantics.