记录一次对NSString和NSMutableString的引用计数操作

记录一次对NSString和NSMutableString的引用计数操作

先将项目变成MRC模式（target->build Settings）

加入下面代码

- (void)viewDidLoad {
    [super viewDidLoad];
    NSString *str0 = [[NSString alloc] init];
    NSMutableString *mStr0 = [[NSMutableString alloc] init];
    NSLog(@"%ld<>%ld",[str0 retainCount],[mStr0 retainCount]); //-1<>1
    NSString *str1 = @"abc";
    NSLog(@"%ld",[str1 retainCount]);//-1
    [str1 retain];
    NSLog(@"%ld",[str1 retainCount]);//-1
    [str1 release];
    NSLog(@"%ld",[str1 retainCount]);//-1
    self.str2 = str1;
    NSLog(@"%ld",[self.str2 retainCount]);//-1
    NSMutableString *str3 = [NSMutableString stringWithFormat:@"%@ccc",str1];
    NSLog(@"str3 = %ld,str4 = %ld",[str3 retainCount],[self.str4 retainCount]);//str3 = 1,str4 = 0
    self.str4 = str3;
    NSLog(@"str3 = %ld,str4 = %ld",[str3 retainCount],[self.str4 retainCount]);//str3 = 2,str4 = 2
    [str3 retain];
    NSLog(@"str3 = %ld,str4 = %ld",[str3 retainCount],[self.str4 retainCount]);//str3 = 3,str4 = 3
}

结论

分析

• NSString是在栈中，栈中变量的生命周期由系统管理，所以对它进行操作是 -1；
• NSMutableString是在堆中分配内存，retainCount表示有多少根强引用线引用着这个对象，当为 0 的时候就回收。