test.cpp

#ifdef _MSC_VER
#define CORRADE_CXX_STANDARD _MSVC_LANG
#else
#define CORRADE_CXX_STANDARD __cplusplus
#endif

#if defined(__clang__) && __clang_major__ >= 9 || defined(__GNUG__) && __GNUG__ >= 9 || defined(_MSC_VER) && _MSC_VER >= 1931
#define CORRADE_CONSTEVAL (__builtin_is_constant_evaluated())
#elif CORRADE_CXX_STANDARD >= 202002L
#define CORRADE_CONSTEVAL (std::is_constant_evaluated()) /*include type_traits*/
#elif __cpp_if_constexpr >= 201606
#define CORRADE_CONSTEVAL constexpr(false)
#else
#define CORRADE_CONSTEVAL (false)
#define CORRADE_NO_CONSTEVAL
#endif

#define STRINGIFY2(x) #x
#define STRINGIFY(x) STRINGIFY2(x)
#define _USE_MATH_DEFINES
#include <cmath>
#include <cstdio>

constexpr float maybe_get_pi()
{
    if CORRADE_CONSTEVAL
        return 3.14;
    else
        return std::atan(1.f)*4;
}

template<typename T> constexpr float my_abs(T x) { return x < 0 ? -x : x; }

#ifdef _MSC_VER
#define VERSION msvc _MSVC_LANG
#elif defined __clang__
#define VERSION clang __clang__ __clang_minor__ 
#elif defined __GNUG__
#define VERSION gcc __GNUC__ __GNUC_MINOR__ 
#else
#define VERSION dunno
#endif

extern const volatile char* str;
const volatile char* str = STRINGIFY(VERSION);

static_assert(my_abs(maybe_get_pi() - M_PI) > 1e-3, "");