[c] printf formatting (%d versus %u)

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

For example:

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

%u is used for unsigned integer. Since the memory address given by the signed integer address operator %d is -12, to get this value in unsigned integer, Compiler returns the unsigned integer value for this address.

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.

%u prints unsigned integer

%d prints signed integer

to get a pointer address use %p

Other List of Formatting Escapes:

Here are the full list of formatting escapes. I am just giving a screen shot from this page

The difference is simple: they cause different warning messages to be emitted when compiling:

1156942.c:7:31: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int *’ [-Wformat=]
     printf("memory address = %d\n", &a); // prints "memory add=-12"
                               ^
1156942.c:8:31: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 2 has type ‘int *’ [-Wformat=]
     printf("memory address = %u\n", &a); // prints "memory add=65456"
                               ^

If you pass your pointer as a void* and use %p as the conversion specifier, then you get no error message:

#include <stdio.h>

int main()
{
    int a = 5;
    // check the memory address
    printf("memory address = %d\n", &a); /* wrong */
    printf("memory address = %u\n", &a); /* wrong */
    printf("memory address = %p\n", (void*)&a); /* right */
}

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