[SOLVED] Compile error when calling std::from

Compile error when calling std::from_chars with a double in libc++

I have a small code as follows:

int main() {
    double d;
    const char* str = "26.50";
    std::from_chars(str, str + strlen(str), d);
    std::cout << d;
}

This code works as expected with libstdc++, but it fails with the following error in libc++ 12.0.0:

candidate template ignored: requirement '__or_<std::__or_<std::is_same<double, signed char>, std::is_same<double, short>, std::is_same<double, int>, std::is_same<double, long>, std::is_same<double, long long>>, std::__or_<std::is_same<double, unsigned char>, std::is_same<double, unsigned short>, std::is_same<double, unsigned int>, std::is_same<double, unsigned long>, std::is_same<double, unsigned long long>>, std::is_same<char, double>>::value' was not satisfied [with _Tp = double]

Is this a libc++ bug? or am I missing something? I should say that this code works if I change data type from double to int.

Solution

libc++ does not support it yet for floating point types.

std::to_chars with floating point types seems to work since clang-16 (godbolt). According to cppreference, it is supported in libc++-14.

std::from_chars for floating point types is not implemented in libc++ as of now.

If you need to use these functions, you will need to link a different C++ standard library, e.g. libstdc++.