Meaning of const pointers as function parameters

Question

I have this function signature:

void myFunction(int *const ptr);

What's the point of the const keyword in this particular context?

Even if ptr wasn't a const variable, I couldn't modify to what address it points to, because it's passed by value, so if I had another function like this:

void myAnotherFunction(int *ptr);

And inside its implementation did something like this:

//...
ptr = malloc(1023);
//...

This wouldn't affect the passed value (outside this function, of course).

So the question is: what's the point of using myFunction() signature instead of myAnotherFunction() one? (beside that you get a compile-time error).

Answer 1

It might make more sense if you consider that the function

void myFunction(int *const ptr);

might be manipulating many pointers, and assigning them and reassigning them, and an invariant of the algorithm it is executing is that the input pointer should never be changed. Then, labeling it const might be very helpful, or at least make you feel more confident that its been implemented correctly.