how do I check if input from cin is a double?

Question

Possible Duplicates:
How to validate numeric input C++
how do I validate user input as a double in C++?

I need to get input from the command line and check if it is a valid number... storing it as a double. If the input is invalid, I need to keep asking for a number.

double x;
cout << '>';
cin >> x;


while (/*x is invalid*/){
 cout << "Invalid Input! Please input a number." << endl;
 cout << '>';
 cin >> x;
}

So how do I check if it is valid?

Answer 1

parse the string and check if there are numbers and 0 or one dot. If these rules aren't met, you just print an error message.

Answer 2

See "How to validate numeric input in C++" - already asked and answered on the site.