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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)

日期：2017-06-08点击：336收藏

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. 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