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 doubleToString(double num)
{
    stringstream s;
    s << num;
    return s.str();
}

Answer 1

You want the strtod function.

bool isOnlyDouble(const char* str)
{
    char* endptr = 0;
    strtod(str, &endptr);

    if(*endptr != '\0' || endptr == str)
        return false;
    return true;
}