Thread: How to print uint32_t variable in hex?

Use "...%x ... "

%x doesn't work. It gives a warning.

Code:

warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]

Should you include stdio.h?

I'm pretty sure I need to use the PRI macros here because I don't know a head of time what size the variable is. For example, uint32_t might be different sizes on different systems (ie, 32-bit vs 64-bit).
Here's the output when I compile with -m32

Code:

sizeof(u32): 4.
sizeof(PRIx16): 2.
sizeof(PRIx32): 2.
sizeof(PRIx64): 4.

Here's the output when I don't compile with -m32

Code:

sizeof(u32): 4.
sizeof(PRIx16): 2.
sizeof(PRIx32): 2.
sizeof(PRIx64): 3.

I'm asking about uint32_t, but I'm using everything in my types.h header, so I need to find away to properly print without knowing the size of the printf specifiers.

Originally Posted by Satya

Should you include stdio.h?

Yes, I do include stdio.h, I just didn't copy and paste it into my post. I didn't think it was necessary. Sorry. It is included though.

The correct PRIx* macro is the way to go. Note that these macros are usually strings and sizeof won't tell you much that is interesting. That result is the size of the memory needed for the string.

Originally Posted by Nominal Animal

Why are you printing the sizes of the printf format patterns? (Edit: Whiteflags already pointed that out; ninja'd me.)

Examine the following instead:

Code:

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

int main(void)
{
    uint8_t  x8  = 240U;
    uint16_t x16 = ~(uint16_t)x8;
    uint32_t x32 = ~(uint32_t)x16;
    uint64_t x64 = ~(uint64_t)x32;

    printf("sizeof x8  = %zu\n", sizeof x8);
    printf("sizeof x16 = %zu\n", sizeof x16);
    printf("sizeof x32 = %zu\n", sizeof x32);
    printf("sizeof x64 = %zu\n", sizeof x64);

    printf("x8 = 0x%02" PRIx8 "\n", x8);
    printf("x16 = 0x%04" PRIx16 "\n", x16);
    printf("x32 = 0x%08" PRIx32 "\n", x32);
    printf("x64 = 0x%016" PRIx64 "\n", x64);
    printf("x64 = %" PRIu64 "\n", x64);

    return EXIT_SUCCESS;
}

Thank you. So PRIx32 works for unsigned and signed? I don't have to specify that it's unsigned?

I made a mistake, actually, I've made a few. Guess it's time to call it a night and relook at things tomorrow. Just been a long day. I figure when I'm making mistakes like this, there's no sense in continuing writing code. Just gonna make more of them.