Objective-C：MRC(引用计数器)在OC内部的可变对象是适用的，不可变对象是不适用的(例如 NSString、NSArray等)

引用计数和字符串

内存中的常量字符串的空间分配与其他对象不同，他们没有引用计数机制

凡是自定义的对象都有引用计数机制；

OC内部中对象分为可变对象(NSMutableString等)和不可变对象(NSString、NSArray等)，

不可变对象不适用于引用计数的机制,可变的对象适用引用计数机制。

 1 //  main.m
 2 //  03-unmutableobject
 3 //
 4 //  Created by ma c on 15/8/13.
 5 //  Copyright (c) 2015年 bjsxt. All rights reserved.
 6 //
 7
 8 #import <Foundation/Foundation.h>
 9
10 int main(int argc, const char * argv[])
11 {
12     @autoreleasepool
13     {
14         //不可变对象不适用于引用计数
15         //1.创建3个对象
16         NSString *str1 = @"hello world";//不可变对象
17
18         NSString *str2 = [NSString stringWithString:@"how arer you"];//不可变对象
19
20         NSMutableString *str3 = [NSMutableString stringWithString:@"I am fine"];//可变对象
21
22         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);
23
24
25         //2.将3个对象添加到可变数组中
26         NSMutableArray *array = [NSMutableArray array];
27         [array addObject:str1];
28         [array addObject:str2];
29         [array addObject:str3];
30         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);
31
32
33         //3.对3个对象做retain操作
34         [str1 retain];
35         [str2 retain];
36         [str3 retain];
37         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);
38
39         //4.将3个对象从数组中删除
40         [array removeObject:str1];
41         [array removeObject:str2];
42         [array removeObject:str3];
43         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);
44
45         //5.对对象做release操作---对应上面的retain操作
46         [str1 release];
47         [str2 release];
48         [str3 release];
49         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);
50
51
52         //6.对对象做release操作---对应上面的对象创建操作(避免内存泄露)
53         [str1 release];
54         [str2 release];
55         [str3 release];
56     }
57     return 0;
58 }

　　　　测试结果是：

2015-08-13 17:41:26.569 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 1
2015-08-13 17:41:26.570 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 2
2015-08-13 17:41:26.571 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 3
2015-08-13 17:41:26.571 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 2
2015-08-13 17:41:26.571 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 1
Program ended with exit code: 0

说明：可以明显看出，NSString是不适用引用计数机制的。