Finding out whether a string is numeric or not

Question

How can we check if a string is made up of numbers only. I am taking out a substring from a string and want to check if it is a numeric substring or not.

NSString *newString = [myString substringWithRange:NSMakeRange(2,3)]; 

Answer 1

Here's one way that doesn't rely on the limited precision of attempting to parse the string as a number:

NSCharacterSet* notDigits = [[NSCharacterSet decimalDigitCharacterSet] invertedSet]; if ([newString rangeOfCharacterFromSet:notDigits].location == NSNotFound) {     // newString consists only of the digits 0 through 9 } 

See +[NSCharacterSet decimalDigitCharacterSet] and -[NSString rangeOfCharacterFromSet:].

Answer 2

I'd suggest using the numberFromString: method from the NSNumberFormatter class, as if the number is not valid, it will return nil; otherwise, it will return you an NSNumber.

NSNumberFormatter *nf = [[[NSNumberFormatter alloc] init] autorelease]; BOOL isDecimal = [nf numberFromString:newString] != nil;