Safely convert std::string_view to int (like stoi or atoi)

Question

Is there a safe standard way to convert std::string_view to int?

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Since C++11 std::string lets us use stoi

Answer 1

Unfortunately, there is no standard way that would throw an exception for you but std::from_chars has a return value code that you may use:

#include 
#include 

template 
void from_chars_throws(const char* first, const char* last, T &t, Args... args) {
    std::from_chars_result res = std::from_chars(first, last, t, args... );

    // These two exceptions reflect the behavior of std::stoi.
    if (res.ec == std::errc::invalid_argument) {
        throw std::invalid_argument{"invalid_argument"};
    }
    else if (res.ec == std::errc::result_out_of_range) {
        throw std::out_of_range{"out_of_range"};
    }
}

Obviously you can create svtoi, svtol from this, but the advantage of "extending" from_chars is that you only need a single templated function.