Printing integers in hex

[skapykat]

Hello.
I am currently reteaching myself C (early stages of learning yet) and I am having an issue with printing the values of an integer in Hex. In the code below, it works correctly until i get to 128 then it decides to print a few f's in front of the the first byte of the hex.

Example print out should look like
FF 00 00 00
but it prints
FFFFFFFF 00 00 00.

Is there an issue in my pointer? it tells me there is a bad ptr when I debug it, but i don't know what is bad about it. Here is my code. Any tips would be appreciated.

#include <stdio.h>
#include <stdlib.h>

int i = 0;

void print_hex_signed_unsigned (int i)
{
 char*
	 hex_ptr = (char*)&i;
 printf("%02x ", hex_ptr[0]);
 printf("%02x ", hex_ptr[1]);
 printf("%02x ", hex_ptr[2]);
 printf("%02x\t", hex_ptr[3]);
 printf("%14d\t", i);
 printf("%14u\n", i);
}

int main ()
{
int index;
    for (index = 0; index < 256; index++)
        print_hex_signed_unsigned(index * 1);
	printf("press enter to continue");
    getchar();
return(0);
}

[tabstop]

This assignment seems familiar, somehow. Anyway, as a char, 128 is actually -128. Since it gets promoted to an int when passed to printf, it is copied by value (so the sign extends with all those 1s, which look like f's when printed in hex). If you don't want that, try (unsigned char *) instead.

[master5001]

Is there a reason you don't just do one printf() call?

[skapykat]

This assignment seems familiar, somehow. Anyway, as a char, 128 is actually -128. Since it gets promoted to an int when passed to printf, it is copied by value (so the sign extends with all those 1s, which look like f's when printed in hex). If you don't want that, try (unsigned char *) instead.

Thanks. That worked perfectly. I think i half tried that before, but forgot to make both unsigned.

[skapykat]

Is there a reason you don't just do one printf() call?

Not really. Just helps me visualize the output a little better.

[master5001]

Fair 'nuff. I once got to thinking about how cool it would be if the optimizer could optimize code by making all encompassing *printf() passes. I guess manual optimizations will always have their place.