C pointers - Point to the same address

Question

#include 
#include 

void foo(int *a, int *b);

void foo(int *a, int *b) {
    *a = 5;
    *b = 6;
    a = b;
}

int main(void) {
    int          


        

Answer 1

The call to foo() ends with its local variables pointing to the same addres, the one of stored in b. This change is not reflected in main(), the caller.

I you liked to actually do this and make this change pemanent, then you would have to pass a pointer to a pointer to foo() (so you can change them), instead of their simple values:

void foo(int **a, int **b) {
    **a = 5;
    **b = 6;
    *a = *b;
}

I have just observed that your code is incompatible with that modification, anyway, since you cannot change two normal variables to point to each other. You'd have to also modify main() this way:

int main(void) {
    int a, b;
    int * ptrA = &a;
    int * ptrB = &b;

    foo(&ptrA, &ptrB);
    printf("%d, %d (%d, %d)", *ptrA, *ptrB, a, b);
    return 0;
}