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。

 

 //  main.m
 //  03-unmutableobject
 //
 //  Created by ma c on 15/8/13.
 //  Copyright (c) 2015年. All rights reserved.
 //

 #import <Foundation/Foundation.h>

 int main(int argc, const char * argv[])
 {
     @autoreleasepool
     {
         //不可变对象不适用于引用计数
         //1.创建3个对象
         NSString *str1 = @"hello world";//不可变对象

         NSString *str2 = [NSString stringWithString:@"how arer you"];//不可变对象

         NSMutableString *str3 = [NSMutableString stringWithString:@"I am fine"];//可变对象

         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);

         //2.将3个对象添加到可变数组中
         NSMutableArray *array = [NSMutableArray array];
         [array addObject:str1];
         [array addObject:str2];
         [array addObject:str3];
         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);

         //3.对3个对象做retain操作
         [str1 retain];
         [str2 retain];
         [str3 retain];
         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);

         //4.将3个对象从数组中删除
         [array removeObject:str1];
         [array removeObject:str2];
         [array removeObject:str3];
         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);

         //5.对对象做release操作---对应上面的retain操作
         [str1 release];
         [str2 release];
         [str3 release];
         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);

         //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)
         [str1 release];
         [str2 release];
         [str3 release];
     }
     return ;
 }

　　　　测试结果是：

-- ::26.569 -unmutableobject[:] str1 = ,str2 = ,str3 =
-- ::26.570 -unmutableobject[:] str1 = ,str2 = ,str3 =
-- ::26.571 -unmutableobject[:] str1 = ,str2 = ,str3 =
-- ::26.571 -unmutableobject[:] str1 = ,str2 = ,str3 =
-- ::26.571 -unmutableobject[:] str1 = ,str2 = ,str3 =
Program ended with exit code: 

说明：可以明显看出，NSString是不适用引用计数机制的。