Template friendly string to numeric in C++

Question

In C++ standard library there are functions to convert from string to numeric types:

stoi
stol
stoll
stoul
stoull
stof
stod
stold

but I find it tedious to use them in template code. Why there are no template functions something like:

template<typename T>
T sto(...)

to convert strings to numeric types?

I don't see any technical reason to not have them, but maybe I'm missing something. They can be specialised to call the underlying named functions and use enable_if/concepts to disable non numeric types.

Are there any template friendly alternatives in the standard library to convert string to numeric types and the other way around in an efficient way?

Answer 1

Why there are no template functions something like:

C++17 has such generic string to number function, but named differently. They went with std::from_chars, which is overloaded for all numeric types.

As you can see, the first overload is taking any integer type as an output parameter and will assign the value to it if possible.

It can be used like this:

template<typename Numeric>
void stuff(std::string_view s) {
    auto value = Numeric{};

    auto [ptr, error] = std::from_chars(s.data(), s.data() + s.size(), value);

    if (error != std::errc{}) {
        // error with the conversion
    } else {
        // conversion successful, do stuff with value
    }
}

As you can see, it can work in generic context.