The stdbool.h interface was introduced in the C99 standard of C language. (See the C data types entry in Wikipedia.) This interface defines the integer constant
true
with value 1 and the integer constant
false
with value 0. Also defines the boolean type
bool
that occupies 1 byte and can only assume the values false and true.
(In the previous, C90, standard of C, the boolean type was defined by the programmer through a typedef:
typedef enum {FALSE, TRUE} boolean;
and a variable of this type occupied sizeof (int) bytes.)