What should the return type be when the function might not have a value to return?

Question

In the old days, you might have a function like this:

const char* find_response(const char* const id) const;

If the item could not be found

Answer 1

I think the second way is better. Or you can write like this:

int find_response(const std::string& id, std::string& value) const;

if this function return -1, it tells that you don't find the response.