Objective-C：MRC(引用計數器)在OC內部的可變對象是適用的，不可變對象是不適用的(例如 NSString、NSArray等)

標籤：

引用計數和字串 記憶體中的常量字串的空間分配與其他對象不同，他們沒有引用計數機制 凡是自訂的對象都有引用計數機制； OC內部中對象分為可變對象(NSMutableString等)和不可變對象(NSString、NSArray等)，不可變對象不適用於引用計數的機制,可變的對象適用引用計數機制。      

 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     @autoreleasepool13     {14         //不可變對象不適用於引用計數15         //1.建立3個對象16         NSString *str1 = @"hello world";//不可變對象17         18         NSString *str2 = [NSString stringWithString:@"how arer you"];//不可變對象19         20         NSMutableString *str3 = [NSMutableString stringWithString:@"I am fine"];//可變對象21         22         NSLog(@"str1 = %lu,str2 = %lu,str3 = %lu",[str1 retainCount],[str2 retainCount],[str3 retainCount]);23         24         25         //2.將3個對象添加到可變數組中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.對3個對象做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.將3個對象從數組中刪除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.對對象做release操作---對應上面的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.對對象做release操作---對應上面的對象建立操作(避免記憶體泄露)53         [str1 release];54         [str2 release];55         [str3 release];56     }57     return 0;58 }

  

　　　　測試結果是：

2015-08-13 17:41:26.569 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 12015-08-13 17:41:26.570 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 22015-08-13 17:41:26.571 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 32015-08-13 17:41:26.571 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 22015-08-13 17:41:26.571 03-unmutableobject[1622:105614] str1 = 18446744073709551615,str2 = 18446744073709551615,str3 = 1Program ended with exit code: 0

 

說明：可以明顯看出，NSString是不適用引用計數機制的。

Objective-C：MRC(引用計數器)在OC內部的可變對象是適用的，不可變對象是不適用的(例如 NSString、NSArray等)