Why is <inttypes.h>'s PRIx16 not equal to “hx”?

Question

Why is PRIx16 == "x" in C (and in C++ ) under GCC?

I would expect it to be "hx" , so that the following works:

#include <inttypes.h>

int16_t v = -1;
printf("%04" PRIx16 "\n", v);  // prints ffffffff, not ffff

Answer 1

Short answer:

To print signed types use d , i .

To print unsigned types, use x , u , o .

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int16_t v is a signed integer type.

PRIxN as in PRIx16 is listed as a "fprintf macros for unsigned integers". PRIxN is not listed for "fprintf macros for signed integers". @Kerrek SB

To print v , as decimal text, use PRId16 or PRIi16 .

printf("%04" PRId16 "\n", v);

To print v as a hexadecimal text, cast/convert to some unsigned.

printf("%04" PRIx16 "\n", (uint16_t)v);

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I also would expect "hx" for PRIx16 and that is the way with my GCC compilation (GNU C11 (GCC) version 6.4.0) yet this is more likely a standard library version issue (mine: ldd (cygwin) 2.9.0). I have doubts about the up-to-date-ness of OP's compiler/library.

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

int main(void) {
  printf(PRIx16);
  return 0;
}

Output

hx