Why does clang's stdbool.h contain #define false false

Question

After being pointed there by a compiler error, I noticed clang\'s stdbool.h file includes (among other things) the following lines:

#define bool  bool
#defin         


        

Answer 1

It was added to suport GNU mode in C++, as we can see from this patch [cfe-commits] r115028 :

Define _Bool, bool, true, and false macros in when we're in a GNU-compatible C++ dialect. Fixes .

so gcc supports this as an extension and this modification was made to support that extension.

Although I can not find the original problem report mentioned in the patch.

This is non-conforming as we can see from the draft C++11 standard section 18.10 Other runtime support [support.runtime]:

The header and the header shall not define macros named bool, true, or false.

but gcc is not meant to be strictly conforming in GNU mode.

stdbool.h is part of C99 and so was not supported by the C++ standard until C++11 which in Annex D says:

For compatibility with the C standard library and the C Unicode TR, the C++ standard library provides the 25 C headers, as shown in Table 154

and includes .