string format with auto conversion of std::string

stringformat.cpp

#include <string>
#include <iostream>
#include <memory>

template<typename T, typename U=T>
U convert(T&& t) {
  return std::forward<T>(t);
}

const char* convert(const std::string& s) {
  return s.c_str();
}

const char* convert(std::string& s) {
  return s.c_str();
}

template<typename ... Args>
std::string stringFormatInternal(const std::string& format, Args&& ... args)
{
  size_t size = snprintf(nullptr, 0, format.c_str(), std::forward<Args>(args) ...) + 1;
  std::unique_ptr<char[]> buf(new char[size]);
  snprintf(buf.get(), size, format.c_str(), args ...);
  return std::string(buf.get(), buf.get() + size - 1);
}

template<typename ... Args>
std::string stringFormat(std::string fmt, Args&& ... args) {
  return stringFormatInternal(fmt, convert(std::forward<Args>(args))...);
}

int main() {
  std::string s = "ctest";
  const std::string s2 = "test";
  const char* cc = "uff";

  std::cout << stringFormat("%s %s %s %s\n", s, s2, "a", cc);

  return 0;
}