Check if NSString contains alphanumeric + underscore characters only in Xcode

Step 1. First create your own character set.

NSCharacterSet *set = [NSCharacterSet characterSetWithCharactersInString:
@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_"];

 Step 2. Once you have that, you invert it to everything that's not in your original string:

set = [set invertedSet];

Step : 3


NSRange r = [string rangeOfCharacterFromSet:s];
if (r.location != NSNotFound) {
  NSLog(@"the string contains illegal characters");
}