Determining if a string is a double

Question

I would like to see if a string contains a double as its sole contents. In other words, if it could possibly be the output of the following function:

string          


        

Answer 1

Or use streams directly:

#include 
#include 
#include 

template
bool isValid(std::string const& num)
{
    T  value;
    std::stringstream stream(num);
    stream >> value;

    // If the stream is already in the error state peak will not change it.
    // Otherwise stream should be good and there should be no more data
    // thus resulting in a peek returning an EOF
    return (stream) &&
           stream.peek() == std::char_traits::eof();
}

int main()
{
    isValid("55");
}