How to form a string using variadic templates without recursion in c++ 11

Question

template <typename ...Args>
void logImpl(tloglevel level, Args&& ...args)
{
    ostringstream stream;
    (stream << ... << std::forward<Args>(args)) << '\n';
    syslog(level, stream.str());
}

func A()
{
int a =10;
std::string b = "test";
logImpl(LOG_INFO, "printing",a,b);
}

func B()
{
unsigned long t = 6700;
logImpl(LOG_INFO, t);
}

I understand that we can achieve it using variadic templates. But is it possible to do it without recursion? fold expression is not an option as only c++ 11 is supported. Please let me know if anyone else has better idea using variadic templates without recursion or fold expression. I want to do it in c++11.

Answer 1

You don't need to use recursion to make this work.

You can create fake array with expanding parameters pack when filling it:

template<class ... Args>
std::string makeString(Args...args){
    std::string s;
    int temp[] = { (s += toString(args),0)... }; // concatenation
    static_cast<void>(temp);
    return s;
}

for toString you provide overloads for handling all types you want.

For example:

template<class T>
std::string toString(T t){
    return std::to_string(t);   // for numbers 
}

std::string toString(const std::string& str){
    return str;
}

std::string toString(const char* str){
    return str;
}

Full demo

---

Hmm, you don't even use toString, version with ostringstream is:

template<class ... Args>
std::string makeString(Args&&...args){
    std::ostringstream os;
    int temp[] = { ((os << std::forward<Args>(args)),0)... };
    static_cast<void>(temp);
    return os.str();
}