Strong vs copy, strongvs

Strong vs copy, strongvs

I. Preface here, I will introduce the differences between strong and copy (the address of the object printed by % p) through an instance ViewController. h

#import <UIKit/UIKit.h>@interface ViewController : UIViewController@property(nonatomic,strong) NSString *name;@endViewController.m  - (void)viewDidLoad {    [super viewDidLoad];    NSMutableString *myName = [NSMutableString stringWithString:@"zhangsan"];    self.name = myName;    NSLog(@"myName's address:%p",myName);    NSLog(@"self.name's address:%p",self.name);} 

The running result is:

2015-07-21 16:38:50.911 Test[4369:2323491] myName's address:0x7967f4c02015-07-21 16:38:50.912 Test[4369:2323491] self.name's address:0x7967f4c0 

When we change strong in. h to copy,

@property(nonatomic,copy) NSString *name;

The running result is:

2015-07-21 16:40:09.938 Test[4394:2330879] myName's address:0x78deb9b02015-07-21 16:40:09.938 Test[4394:2330879] self.name's address:0x78dea270

Comparison shows that when strong is used, the addresses of the myName object and self. name are the same, indicating that the two point to the same address space: 0x7967f4c0 When we change strong of name in. h to copy, the myName and self. name addresses are different, indicating that the two point to different address spaces. MyName is: 0x78deb9b0Self. name is: 0x78dea270This Note: When we use copy, it means that we have different buckets and store the same content. Therefore, if we modify myName, self. name will not be affected. Conclusion: here you should learn: 1. The difference between strong and copy 2. We can print the object address with % p.