C Formatting Question (%d versus %u)

Question

What is difference between %d and %u when printing pointer addresses?

For example:

int a=5;
// check the memory address
printf("memory add=%d\n", &a); // prints "memory add=-12"
printf("memory add=%u\n", &a); // prints "memory add=65456"

Please define.

Answer 1

You can find a list of formatting escapes on this page.

%d is a signed integer, while %u is an unsigned integer. Pointers (when treated as numbers) are usually non-negative.

If you actually want to display a pointer, use the %p format specifier.

Answer 2

If I understand your question correctly, you need %p to show the address that a pointer is using, for example:

int main() {
    int a = 5;
    int *p = &a;
    printf("%d, %u, %p", p, p, p);

    return 0;
}

will output something like:

-1083791044, 3211176252, 0xbf66a93c