The
<stdbool.h> header defines four macros:
1.
bool, which expands to _Bool;
2.
true, which expands to the integer constant 1;
3.
false, which expands to the integer constant 0; and
4.
__bool_true_false_are_defined, which expands to the constant 1.
The ability to undefine and redefine the macros
bool,
true, and
false is an obsolescent feature that may be withdrawn in a future version of a standard.