引用計數和字符串 內存中的常量字符串的空間分配與其他對象不同，他們沒有引用計數機制 凡是自定義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)， 不可變對象不適用于引用計數的機制,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. All rights reserved. 6 // 7 8 #import <Foundation/Foundation.h> 9 10 int main(int argc, const char * argv[]) 11 { 12 @autoreleasepool 13 { 14 //不可變對象不適用于引用計數 15 //1.創建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---對應上面的對象創建操作(避免內存泄露) 53 [str1 release]; 54 [str2 release]; 55 [str3 release]; 56 } 57 return 0; 58 }

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　　　　測試結果是：

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

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說明：可以明顯看出，NSString是不適用引用計數機制的。

轉載于:https://www.cnblogs.com/XYQ-208910/p/4728026.html

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