format specifiers for uint32_t and size_t

Question

Hello,

gcc 4.4.4 c89 -Wall -Wextra

I have the following

size_t   i = 0;
uint32_t k = 0;

printf("i [ %lu ] k [ %u ]\n", i, k);

I get the following warning when compiling:

format ‘%lu’ expects type ‘long unsigned int’, but argument has type ‘uint32_t’

When I ran this using splint I got the following:

Format argument 1 to printf (%u) expects unsigned int gets size_t: k

Many thanks for any advice,

Steve

Answer 1

Sounds like you're expecting size_t to be the same as unsigned long (possibly 64 bits) when it's actually an unsigned int (32 bits). Try using %u in both cases.

I'm not entirely certain though.

Answer 2

Try

#include <inttypes.h>
...

printf("i [ %zu ] k [ %"PRIu32" ]\n", i, k);

The z represents an integer of length same as size_t, and the PRIu32 macro, defined in the C99 header inttypes.h, represents an unsigned 32-bit integer.

Answer 3

If you don't want to use the PRI* macros, another approach for printing ANY integer type is to cast to intmax_t or uintmax_t and use "%jd" or %ju, respectively. This is especially useful for POSIX (or other OS) types that don't have PRI* macros defined, for instance off_t.