Pass unknown type and quantity of args and concat to char array

Question

Is there a way to pass unknown quantity of args which can be either char strings or integers into a function and then concatenate them to a char array buffer?

For example, to be able to call all the following functions:

bufcat("this", 1, 3, "that");  
// buffer = "this13that"
bufcat(1, "this", "that", 3, 4000000, "other");
// buffer = "1thisthat34000000other"
bufcat(1000000,2,3,4,5,6,7,8,9,10,11,12,13,"onemillionandfiftytwo");
// buffer = "10000002345678910111213onemillionandfiftytwo"

Answer 1

A simple solution is possible in c++11 using variadic templates. If performance matters the boilerplate code needed for the classic printf idiom might be more acceptable than the memory allocations used here.

#include <string>
#include <iostream>
inline std::string bufcat() { return ""; }
template<typename value_type> std::string bufcat(const value_type &value)    { return std::to_string(value); }
template<> std::string bufcat(const bool &b) { return b ? "true" : "false"; }
std::string bufcat(const std::string &str) { return str; }
std::string bufcat(const char *str) { return str; }
template <typename arg0_type, typename ...arg_types>
std::string bufcat(arg0_type arg0, arg_types ... args)
{ return bufcat(arg0).append(bufcat(args...)); }

int main()
{
    std::cout << bufcat(1000000,2,3,4,5,6,7,8,9,10,11,12,13,"onemillionandfiftytwo") << "\n";
}

Answer 2

You can use variadic template plus a string stream:

template<typename... Args>
std::string bufcat(Args&&... args) {
    std::stringstream ss;

    auto iteration = [&ss](auto&& item) { ss << std::forward<decltype(item)>(item); };

    (void)std::initializer_list<int> {(
        iteration(std::forward<Args>(args))
    , 0)..., 0};

    return ss.str();
}

This will concat anything that you pass in parameters into the string stream. It will call the iteration lambda for each arguments in Args.

Then, you can simply call your function like this:

bufcat(1000000,2,3,4,5,6,7,8,9,10,11,12,13,"onemillionandfiftytwo");

And it will yield 10000002345678910111213onemillionandfiftytwo