Converting pre-ANSI C function declarations with fixed array sizes to ANSI

Question

I'm new to C (well, RUSTY in C at least) and I'm working on some pre-ANSI C code in Visual Studio 2010. It compiles fine, but Intellisense is going crazy over the function declarations:

int add()
    int a, int b;
{
    return a + b;
}

instead of the ANSI

int add(int a, int b) 
{
    return a + b;
}

But I'm running into a few instances of arrays with bounds in function declarations, and I don't think that can be converted directly to ANSI C.

int add() 
    int a[5], int b[5];
{
    ...
}

The below compiles cleanly, but does this mean the exact same thing?

int add(int a[5], int b[5]) {
}

Answer 1

Yes, it means the same thing, but it doesn't (and never did) really mean what it looked like it should mean.

The parameters are really pointers. By inference, there should be 5 elements in the arrays that they point to, but that isn't going to be guaranteed. In particular, given:

extern int add(int a[5], int b[5]);

int x[4];
int y[6];

add(x, y);

This is not going to cause the compiler to throw warnings.

With C99, you could let the optimizer assume that there will be at least 5 entries using the (weird) notation:

int add(int a[static 5], int b[static 5]) { ... }

Even this doesn't necessarily cause warnings at the call site; it is information to the compiler (though whether it uses it or not is up to the compiler).