iOS copy与strong声明属性时的区别

xcode版本：8.3.3

//
//  ViewController.m
//  内存管理
//
//  Created by walg on 2017/8/9.
//  Copyright © 2017年 walg. All rights reserved.
//

#import "ViewController.h"
#import "SecondViewController.h"
@interface ViewController ()

@property (nonatomic, strong) NSMutableString *strM;
@property (nonatomic, strong) NSString *str;

@property (nonatomic, copy) NSString *strC1;
@property (nonatomic, copy) NSString *strC2;
@property (nonatomic, copy) NSMutableString *strC3;
@property (nonatomic, copy) NSMutableString *strC4;

@property (nonatomic, strong) NSString *strS1;
@property (nonatomic, strong) NSString *strS2;
@property (nonatomic, strong) NSMutableString *strS3;
@property (nonatomic, strong) NSMutableString *strS4;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
//    self.strM = [NSString stringWithFormat:@"abc"];
    
    self.strM = [NSMutableString stringWithFormat:@"abc"];
    
    
    self.strC1 = self.strM;
    self.strS1 = self.strM;
    
    self.strC3 = self.strM;
    self.strS3 = self.strM;
    
    self.strC2 =  [NSString stringWithFormat:@"%@",self.strM];
    self.strS2 =  [NSString stringWithFormat:@"%@",self.strM];
    
    self.strC4 =  (NSMutableString*)[NSString stringWithFormat:@"%@",self.strM];
    self.strS4 =  (NSMutableString*)[NSString stringWithFormat:@"%@",self.strM];
    
    NSLog(@"---------->>>开始<<<----------");
    NSLog(@"Ori_address----->>>>>>：value:%@---%p==%p",_strM,_strM,&_strM);
    NSLog(@"address----->>>>>>C1：value:%@---%p==%p",_strC1,_strC1,&_strC1);
    NSLog(@"address----->>>>>>S1：value:%@---%p==%p",_strS1,_strS1,&_strS1);
    NSLog(@"address----->>>>>>C2：value:%@---%p==%p",_strC2,_strC2,&_strC2);
    NSLog(@"address----->>>>>>S2：value:%@---%p==%p",_strS2,_strS2,&_strS2);
    NSLog(@"address----->>>>>>C3：value:%@---%p==%p",_strC3,_strC3,&_strC3);
    NSLog(@"address----->>>>>>S3：value:%@---%p==%p",_strS3,_strS3,&_strS3);
    NSLog(@"address----->>>>>>C4：value:%@---%p==%p",_strC4,_strC4,&_strC4);
    NSLog(@"address----->>>>>>S4：value:%@---%p==%p",_strS4,_strS4,&_strS4);
    NSLog(@"---------->>>结束<<<----------\n");

}

-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    
    
//    self.strM = [_strM stringByAppendingString:@"de"];
    [_strM appendString:@"de"];
    
    NSLog(@"---------->>>点击开始输出<<<----------");
    NSLog(@"Ori_address<<<<<<----->>>>>>：value:%@---%p==%p",_strM,_strM,&_strM);
    NSLog(@"address<<<<<<----->>>>>>C1：value:%@---%p==%p",_strC1,_strC1,&_strC1);
    NSLog(@"address<<<<<<----->>>>>>S1：value:%@---%p==%p",_strS1,_strS1,&_strS1);
    NSLog(@"address<<<<<<----->>>>>>C2：value:%@---%p==%p",_strC2,_strC2,&_strC2);
    NSLog(@"address<<<<<<----->>>>>>S2：value:%@---%p==%p",_strS2,_strS2,&_strS2);
    NSLog(@"address<<<<<<----->>>>>>C3：value:%@---%p==%p",_strC3,_strC3,&_strC3);
    NSLog(@"address<<<<<<----->>>>>>S3：value:%@---%p==%p",_strS3,_strS3,&_strS3);
    NSLog(@"address<<<<<<----->>>>>>C4：value:%@---%p==%p",_strC4,_strC4,&_strC4);
    NSLog(@"address<<<<<<----->>>>>>S4：value:%@---%p==%p",_strS4,_strS4,&_strS4);
    NSLog(@"---------->>>点击结束输出<<<----------\n");

}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}


@end

《点了两次》

2017-08-09 18:17:29.112 内存管理[31855:14351521] ---------->>>开始<<<----------
2017-08-09 18:17:29.112 内存管理[31855:14351521] Ori_address----->>>>>>：value:abc---0x60800026ba40==0x7f86d0421748
2017-08-09 18:17:29.112 内存管理[31855:14351521] address----->>>>>>C1：value:abc---0xa000000006362613==0x7f86d0421758
2017-08-09 18:17:29.113 内存管理[31855:14351521] address----->>>>>>S1：value:abc---0x60800026ba40==0x7f86d0421778
2017-08-09 18:17:29.113 内存管理[31855:14351521] address----->>>>>>C2：value:abc---0xa000000006362613==0x7f86d0421760
2017-08-09 18:17:29.113 内存管理[31855:14351521] address----->>>>>>S2：value:abc---0xa000000006362613==0x7f86d0421780
2017-08-09 18:17:29.113 内存管理[31855:14351521] address----->>>>>>C3：value:abc---0xa000000006362613==0x7f86d0421768
2017-08-09 18:17:29.113 内存管理[31855:14351521] address----->>>>>>S3：value:abc---0x60800026ba40==0x7f86d0421788
2017-08-09 18:17:29.113 内存管理[31855:14351521] address----->>>>>>C4：value:abc---0xa000000006362613==0x7f86d0421770
2017-08-09 18:17:29.114 内存管理[31855:14351521] address----->>>>>>S4：value:abc---0xa000000006362613==0x7f86d0421790
2017-08-09 18:17:29.114 内存管理[31855:14351521] ---------->>>结束<<<----------
2017-08-09 18:19:13.818 内存管理[31855:14351521] ---------->>>点击开始输出<<<----------
2017-08-09 18:19:13.819 内存管理[31855:14351521] Ori_address<<<<<<----->>>>>>：value:abcde---0x60800026ba40==0x7f86d0421748
2017-08-09 18:19:13.820 内存管理[31855:14351521] address<<<<<<----->>>>>>C1：value:abc---0xa000000006362613==0x7f86d0421758
2017-08-09 18:19:13.820 内存管理[31855:14351521] address<<<<<<----->>>>>>S1：value:abcde---0x60800026ba40==0x7f86d0421778
2017-08-09 18:19:13.820 内存管理[31855:14351521] address<<<<<<----->>>>>>C2：value:abc---0xa000000006362613==0x7f86d0421760
2017-08-09 18:19:13.820 内存管理[31855:14351521] address<<<<<<----->>>>>>S2：value:abc---0xa000000006362613==0x7f86d0421780
2017-08-09 18:19:13.820 内存管理[31855:14351521] address<<<<<<----->>>>>>C3：value:abc---0xa000000006362613==0x7f86d0421768
2017-08-09 18:19:13.820 内存管理[31855:14351521] address<<<<<<----->>>>>>S3：value:abcde---0x60800026ba40==0x7f86d0421788
2017-08-09 18:19:13.821 内存管理[31855:14351521] address<<<<<<----->>>>>>C4：value:abc---0xa000000006362613==0x7f86d0421770
2017-08-09 18:19:13.845 内存管理[31855:14351521] address<<<<<<----->>>>>>S4：value:abc---0xa000000006362613==0x7f86d0421790
2017-08-09 18:19:13.845 内存管理[31855:14351521] ---------->>>点击结束输出<<<----------
2017-08-09 18:19:19.625 内存管理[31855:14351521] ---------->>>点击开始输出<<<----------
2017-08-09 18:19:19.626 内存管理[31855:14351521] Ori_address<<<<<<----->>>>>>：value:abcdede---0x60800026ba40==0x7f86d0421748
2017-08-09 18:19:19.626 内存管理[31855:14351521] address<<<<<<----->>>>>>C1：value:abc---0xa000000006362613==0x7f86d0421758
2017-08-09 18:19:19.626 内存管理[31855:14351521] address<<<<<<----->>>>>>S1：value:abcdede---0x60800026ba40==0x7f86d0421778
2017-08-09 18:19:19.626 内存管理[31855:14351521] address<<<<<<----->>>>>>C2：value:abc---0xa000000006362613==0x7f86d0421760
2017-08-09 18:19:19.626 内存管理[31855:14351521] address<<<<<<----->>>>>>S2：value:abc---0xa000000006362613==0x7f86d0421780
2017-08-09 18:19:19.627 内存管理[31855:14351521] address<<<<<<----->>>>>>C3：value:abc---0xa000000006362613==0x7f86d0421768
2017-08-09 18:19:19.627 内存管理[31855:14351521] address<<<<<<----->>>>>>S3：value:abcdede---0x60800026ba40==0x7f86d0421788
2017-08-09 18:19:19.627 内存管理[31855:14351521] address<<<<<<----->>>>>>C4：value:abc---0xa000000006362613==0x7f86d0421770
2017-08-09 18:19:19.628 内存管理[31855:14351521] address<<<<<<----->>>>>>S4：value:abc---0xa000000006362613==0x7f86d0421790
2017-08-09 18:19:19.628 内存管理[31855:14351521] ---------->>>点击结束输出<<<----------

可以看到：
一、在接收NSMutableString的值时：
（1）@property (nonatomic, strong) NSString *strS2; 用“=”赋值时，_strS2 与_strC3的值指向同一内存地址。当_strC3改变时，_strS2也跟着改变。
（2）@property (nonatomic, copy) NSString *strC2; 用“=”赋值时，_strC2 与_strC3的值指向新的内存地址。当_strC3改变时，_strC2不跟着改变。
（3）[NSString stringWithFormat:@"%@",self.strC3]当用这种方式赋值时，无论是copy还是strong都会开辟新的地址，与原来的都没有关联。
（4）以上跟NSMutableString还是NSString无关。
二、在接收NSString的值时，都是开辟新的地址。互不影响，与copy和strong无关！