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 
      
        9 10 int main(int argc, const char * argv[])11 {12     @autoreleasepool13     {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 = 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

 

说明：可以明显看出，NSString是不适用引用计数机制的。