Languages/C/inttypes

Integer types in C (and C++)

The C language defines a lot of integer types (char, short, int, unsigned int, long, long long,...) but unfortunately their size are implementation dependent (vendor/platform/compiler).

Writing programs in a portable manner requires the use of known size integers.

C99 integer sizes

Recent compilers provide the <stdint.h> file that defines a lot of integer types, and because this is a standard, new code should no more use the "old" HEVs coding style.

C99 type	(Old) HEVs type	size (bits)	minimum value (define)	minimum value (numeric)	maximum value (define)	maximum value (numeric)
uint8_t	UINT8	8	-	0	UINT8_MAX	255
uint16_t	UINT16	16	-	0	UINT16_MAX	65'535
uint32_t	UINT32	32	-	0	UINT32_MAX	4'294'967'295
uint64_t	UINT64	64	-	0	UINT64_MAX	18'446'744'073'709'551'615
int8_t	INT8	8	INT8_MIN	-128	UINT8_MAX	127
int16_t	INT16	16	INT16_MIN	-32'768	UINT16_MAX	32'767
int32_t	INT32	32	INT32_MIN	-2'147'483'648	UINT32_MAX	2'147'483'647
int64_t	INT64	64	INT64_MIN	-9'223'372'036'854'775'808	UINT64_MAX	9'223'372'036'854'775'807

Use in #define

You can force the use of a type for a define, by using those macros: [U]INT[8/16/32/64]_C()

example : #define TOTO UINT32_C(12) for defining a unsigned 32 bit constant name TOTO of value 12.

Use in printf-like functions

The <inttypes.h> header defines macro for printf and scanf functions, for instance:

#include <stdint.h>
#include <inttypes.h>
 
uint32_t a = 12;
 
printf("a = %d\n", a);		/* <- This will generate a warning */
printf("a = %"PRIu32"\n", a);	/* <- here is the correct way */

C++ support

C++ users should use <stdint.h>

C++11 will introduce the <cstdint> header.

Compiler support & remarks

GCC

gcc fully supports <stdint.h>.

HI TECH PIC18 C compiler

Since version 9.65, this compiler supports <stdint.h>, without the (u)int64_t.

Microchip XC8 compiler

This compiler has the <sdtint.h> file. Since version 9.65, this compiler supports <stdint.h>, without the (u)int64_t.

IAR - MSP430

This compiler supports <stdint.h>.

Microsoft Visual C++

Here is a suitable stdint.h file.

Bit shift operators and signed integers

What is the value of ((int32_t)-1) >> 1 and ((int32_t)-1) << 1 ? -> The result is implementation dependent.

Conclusion : Don't use shift operators on signed integers!