NSMutableString *mStr = [NSMutableString stringWithCapacity:100]; NSLog(@"%@", mStr); [mStr appendFormat:@"%@",@"123"]; NSLog(@"%@", mStr); NSRange r = {0,2}; [mStr replaceCharactersInRange:r withString:@"hehe"]; NSLog(@"%@", mStr); [mStr deleteCharactersInRange:r]; NSLog(@"%@", mStr);