Is there any generic conversion from std::string to numeric type?

Question

There are many ways to convert strings to numbers in C++: stoi, stod, stof, etc. Just like how std::invoke is a nice way to call any callable, I am looking for a method that converts string value to a generic numeric value.

For instance, instead of something like this:

int x = std::stoi("5");
long y = std::stol("5555555555");

Something like this:

int x = num_convert("55");
long y = num_convert("5555555555");

Is there any standard functionality for what I am trying to do?

Answer 1

This can be considered as a generic conversion:

#include<sstream>

int main() {
  int x;
  std::stringstream("55") >> x;

  long y;
  std::stringstream("5555555555") >> y;
}

A function can return only a single type, thus long y = num_convert("5555555555") with a regular function is impossible.

One more hack, help the function to deduce the returned type with the unused parameter:

#include <string>

template<typename T>
T num_convert(const char* s, const T&) {
  return static_cast<T>(std::stoll(s));
}

int main() {
  int x = num_convert("55", x);
  long y = num_convert("5555555555", y);
}