<cstdbool> (stdbool.h)

Boolean type
The purpose in C of this header is to add a bool type and the true and false values as macro definitions.

In C++, which supports those directly, the header simply contains a macro that can be used to check if the type is supported:

Macro constants

Macrodescriptiondefined as
__bool_true_false_are_definedSpecifies whether bool, true and false are defined1