constexpr specifier (since C23)
A scalar object declared with the constexpr storage-class specifier is a constant. It must be fully and explicitly initialized according to the static initialization rules. It still has linkage appropriate to its declaration and it exist at runtime to have its address taken; it simply cannot be modified at runtime in any way, i.e. the compiler can use its knowledge of the object’s fixed value in any other constant expression.
# Example
#include <fenv.h>
#include <stdio.h>
int main(void)
{
constexpr float f = 23.0f;
constexpr float g = 33.0f;
fesetround(FE_TOWARDZERO);
constexpr float h = f / g; // is not affected by fesetround() above
printf("%f\n", h);
}