C++ :: Template Function Don't Work As Inline Function?

I have this:

string input;
unsigned short choice;
...
istringstream valid(input);
...
if(!(valid >> choice))
{
//some error
}

Ok. My code is almost 1000 lines, and I have splited some functions in headers. But the same function doesn't work:

template <typename T> bool valid_input(const string& input, T var)
{
istringstream valid(input);
return (valid >> var);
}

You can check it here: [URL] The output is correct, but in my machine with C++11, MinGW 4.8 (64 bit in a 64bit-Windows8), the output is incorrect. Why?

If you want more specific info, the problem is that I use input, I think. I use std::getline(std::cin, some_string).