Compile error with templates - no matching function for call

Question

I'm trying to convert a string to a number. For that, I found the following way:

#include <iostream>
#include <string>

template <typename T>
T stringToNumber(const std::string &s)
{
    std::stringstream ss(s);
    T result;
    return ss >> result ? result : 0;
}

int main()
{
    std::string a = "254";
    int b = stringToNumber(a);

    std::cout << b*2 << std::endl;
}

The problem is that I am getting the following error:

error: no matching function for call to ‘stringToNumber(std::string&)’

May anyone tell me why I am getting such error and how to fix it?

Thank you in advance.

Answer 1

Try

int b = stringToNumber<int>(a);

Because the template type T can not be deduced from any of the parameters (in this case std::string) you need to explicitly define it.

Answer 2

You haven't supplied a template argument. Note that in C++11, you can use std::stoi:

std::string a = "254";
int b = std::stoi(a);