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 exists 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 .

Additionally, the constant expression that is used for the initializer of such a constant is checked at compile time.

An initializer of floating-point type must be evaluated with the translation-time floating-point environment.

There are some restrictions on the type of an object that can be declared with constexpr . Namely, the following constructs are not allowed to be constexpr :

• Pointers (except that null pointers can be constexpr ),
• Variably modified types,
• Atomic types ,
• volatile types,
• restrict pointers.

Keywords

constexpr

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);
}

0.696969

References

See also