Passing by pointer

Question

I am confused between these two functions:

void Swap_byPointer1(int *x, int *y){
    int *temp=new int;
    temp=x;
    x=y;
    y=temp;
}

---

void Swap_byPointer2(int *x, int *y){
    int *temp=new int;
    *temp=*x;
    *x=*y;
    *y=*temp;
}

Why Swap_byPointer2 succeeds to swap between x and y, and Swap_byPointer1does not?

Answer 1

In your first function you're swapping the pointers themselves, and in the second you're swapping the values of what the pointers point to, ie pointers dereferenced.

If you want to change what a pointer points to, you should pass a pointer to a pointer (ie int**x) and change the second pointer.

Like so

void Swap_byPointer1(int **x, int **y){
    int *temp;
    temp=*x;
    *x=*y;
    *y=*temp;
}