[c++] std::is_constant

[c++] std::is_constant_evaluated()

11 Dec 2023

Example

Here’s an example of how you can use std::is_constant_evaluated() in your code:

#include <iostream>
#include <type_traits>

constexpr int square(int x) {
    if (std::is_constant_evaluated()) {
        return x * x;
    } else {
        return x + x;
    }
}

int main() {
    std::cout << square(5) << std::endl;  // Output will be 10 at runtime
    constexpr int res = square(5);  // Compile-time evaluation result is 25
    return 0;
}

In this example, std::is_constant_evaluated() is used to conditionally perform different computations based on whether the function is being evaluated at compile time or run time.

References

cppreference - std::is_constant_evaluated