OC-NSString除去两边的空格，类似java中的trim

OC-NSString去掉两边的空格，类似java中的trim

NSString *str = @"  abcd   ";NSString *str2 = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];NSLog(@"%@",str);NSLog(@"%@",str2);