Question

I am writing some code to get a hex dump of the stack in c. I keep getting a compile error on this following line when I compile it using gcc in ubuntu however it compiles fine under gcc in windows.

char buffer[10];
for (int i=0;i<20;i++)
    printf("0x%lx => 0x%lx\n", &(buffer[i]), ((long *)buffer)[i]);

This is the message the compiler gives.

warning: format ‘%lx’ expects type ‘long unsigned int’, but argument 2 has type ‘char *’

Can someone please tell me if I am doing someting wrong?

Answer 1

Try:

char buffer[10];
for (int i=0;i<20;i++)
    printf("%p => 0x%lx\n", (void*)&(buffer[i]), ((long *)buffer)[i]);

The 2nd arg, &(buffer[i]) is of type char*, so it needs a cast and a %p.

The 3rd arg, ((long *)buffer)[i], is of type long, so it needs a %lx.

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Aside: Please realize that if buffer is not long-aligned, you might get the right answer, the wrong answer, or a core dump, all depending upon your CPU, OS, OS settings, and/or compiler.

If it were me, I’d try:

long l;
for(int i = 0; i < 20; i++)
    printf("%p => 0x%lx\n", (void*)(&l+i), *(&l+i));