printf conversion specifier for _Bool?

Question

With printf(), I can use %hhu for unsigned char, %hi for a short int, %zu for a size_t

Answer 1

There is no. Just handling it like an int by using %d or %i specifier.

_Bool

In C99, a new keyword, _Bool, is introduced as the new boolean type. In many aspects, it behaves much like an unsigned int, but conversions from other integer types or pointers always constrained to 0 and 1. Other than for other unsigned types, and as one would expect for a boolean type, such a conversion is 0 if and only if the expression in question evaluates to 0 and it is 1 in all other cases. The header stdbool.h provides macros bool, true and false that are defined as _Bool, 1 and 0, respectively.

The first way to implement it that come from into mind is by using a char or(int8_t) an enum and with bit fields. But actually, it depends. It can be a typedef for an int(as I've mentioned, it's used, but is not recommend, subject to bugs) or char or unsigned int or an enum and #define that's commonly used.

For exampe, Apple's implementation uses int,as you can see:

#ifndef _STDBOOL_H_
#define _STDBOOL_H_ 

#define __bool_true_false_are_defined   1

#ifndef __cplusplus

#define false   0
#define true    1

#define bool    _Bool
#if __STDC_VERSION__ < 199901L && __GNUC__ < 3
typedef int _Bool;
#endif

#endif /* !__cplusplus */

#endif /* !_STDBOOL_H_ */

Others implementations:

typedef int8_t _Bool;

typedef enum { false = 0, true = 1 } bool;

typedef unsigned char Boolean; typedef _Bool Boolean;