Printing values with C Format Strings

In order to ensure compiler and platform portability use the following rules for C format strings.

Assumption: A value of 16/32 or 64bit length needs to be printed with a C99 format string.

• Until 16-bit length: use %d for signed and %u for unsigned. No casts are needed.
• 32-bit length: use %ld for signed and %lu for unsigned. Cast to long or unsigned long, respectively.
• 64-bit length: use %lld for signed and %llu for unsigned. Cast to long long or unsigned long long, respectively.
• size_t: use %zu.
• Hex:
  • Until 16-bit length use %x.
  • 32-bit length use %lx and cast to unsigned long.
  • 64-bit length use %llx and cast to unsigned long long.

Individual cases:

Value	Format string	Reason
char	"%d"	Is promoted to int.
short	"%d"	Is promoted to int. Minimal width: 16bit.
int	%d	Minimal width: 16bit (int16_t).
long	%d or %ld	Minimal width: 32bit (int32_t).
long long	%lld	Minimal width: 64bit (int64_t).
int8_t	%d	Is promoted to int.
int16_t	%d	Is promoted to int.
int32_t	%ld	Cast to long required.
int64_t	%lld	Cast to long long required.
unsigned char	%d	Is promoted to int
unsigned short	%u
unsigned int	%u	Minimal width: 16bit (uint16_t)
unsigned long	%lu	Minimal width: 32bit (uint32_t)
unsigned long long	%llu	Minimal width: 64bit (uint64_t)
uint8_t	%u or %d	Is promoted to int.
uint16_t	%u	Is promoted to int.
uint32_t	%lu	Cast to unsigned long required.
uint64_t	%llu	Cast to unsigned long long required.
size_t	%zu
float	%f or %g	Promoted to double for printing (compiler dependent).
double	%f or %g
void *	%p
hex(uint8_t)	%x or %X
hex(uint16_t)	%x or %X
hex(uint32_t)	%lx or %lX	Cast to unsigned long required.
hex(uint64_t)	%llx or %llX	Cast to unsigned long long required.

For more information see this manpage.