jett jett - 28 days ago 17
C++ Question

Concatenating strings (and numbers) in variadic template function

I am attempting to write a function that takes a variety of strings or numbers (that work with

std::to_string
and concatenate them. I've got it working with just strings, but I am having trouble with specializing depending on input as string or number.

My code is called like this:

stringer("hello", "world", 2, 15, 0.2014, "goodbye", "world")


And here is what I've got:

inline std::string stringer(const std::string &string)
{
return string;
}

template <typename T, typename... Args>
inline std::string stringer(const std::string &string, T &&val, Args &&...args)
{
return stringer(string+std::to_string(val), std::forward<Args>(args)...);
}

template <typename... Args>
inline std::string stringer(const std::string &string, Args &&...args)
{
return stringer(string, std::forward<Args>(args)...);
}


Currently it is breaking on any more than one string added unless the following are all numbers (due to the to_string). How can I specialize based on string or number to make the above work? Thanks.

Answer
inline std::string const& to_string(std::string const& s) { return s; }

template<typename... Args>
std::string stringer(Args const&... args)
{
    std::string result;
    using ::to_string;
    using std::to_string;
    int unpack[]{0, (result += to_string(args), 0)...};
    static_cast<void>(unpack);
    return result;
}