Objective-C中的字符串操作

NSString *str1 = @"Hello";
NSString *str2 = @"World";
NSString *result = [str1 stringByAppendingString:str2];

NSString *str = @"Hello World";
NSString *result = [str substringFromIndex:6];

NSString *str1 = @"Hello";
NSString *str2 = @"World";
NSComparisonResult result = [str1 compare:str2];

NSString *str = @"Hello World";
NSRange range = [str rangeOfString:@"World"];