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, %tx for a ptrdiff_t, etc.

What conversion format specifier do I use for a _Bool? Does one exist in the standard?

Or do I have to cast it like this:

_Bool foo = 1;
printf("foo: %i\n", (int)foo);

Answer 1

There is no specific conversion length modifier for _Bool type.

_Bool is an unsigned integer type large enough to store the values 0 and 1. You can print a _Bool this way:

_Bool b = 1;
printf("%d\n", b);

Because of the integer promotions rules, _Bool is guaranteed to promote to int.