#if true evaluates to false in C++ and C23 #711

In #if and #elif expressions, simplecpp treats true and false like any other unknown name and replaces them with 0. So #if true is false.

In C++, true and false are keywords. The standard says they are not replaced with 0 in #if expressions; they evaluate to 1 and 0 ([cpp.cond]). C23 made them keywords too, and they also evaluate to 1 and 0 in #if (C23
§6.10.2).

Example

#if true
yes
#else
no
#endif

• Expected (gcc -E -std=c++20 or -std=c23): yes
• Actual (simplecpp): no