6.12.9 Support for the _Bool Type

The C99 standard added _Bool as a C language keyword naming the boolean type. As an extension, GNU C also recognizes _Bool in C90 mode as well as with -std=c99 and later.

C23 added bool as the preferred name of the boolean type, but _Bool also remains a standard keyword in the language and is supported as such by GCC with -std=c23.

GNU C++ does not support _Bool as a keyword, but including <stdbool.h> defines it as a macro in terms of standard C++s bool type.