字符串中的retain与copy

 NSMutableString *mStr = [NSMutableString
string];

    

    [mStr setString:@"我没变"];

    

    

    

    self.retainStr   = mStr;

    

    self.cpStr     = mStr;

    

    self.retainMStr = mStr;

    

    self.cpMStr   = mStr;

    

    

    

    NSLog(@"retainStr:%@", 
self.retainStr);

    

    NSLog(@"copyStr:%@",   
self.cpStr);

    

    NSLog(@"retainMStr:%@",
self.retainMStr);

    

    NSLog(@"copyMStr:%@",  
self.cpMStr);

    

    NSLog(@"\n");

    

    

    

    [mStr setString:@"我变了"];

    

    

    

    NSLog(@"retainStr:%@", 
self.retainStr);

    

    NSLog(@"copyStr:%@",   
self.cpStr);

    

    NSLog(@"retainMStr:%@",
self.retainMStr);

    

    NSLog(@"copyMStr:%@",  
self.cpMStr);

    

    NSLog(@"\n");

    

    

    

    NSString *str =
@"我来了";//[[NSString alloc] initWithFormat:@"我来了"];//两种方式都一样。

    

    self.retainStr  = str;

    

    self.cpStr    = str;

    

    self.retainMStr = [str
mutableCopy];

    

    self.cpMStr   = [str
mutableCopy];

    

    

    

    NSLog(@"retainStr:%@", 
self.retainStr);

    

    NSLog(@"copyStr:%@",   
self.cpStr);

    

    NSLog(@"retainMStr:%@",
self.retainMStr);

    

    NSLog(@"copyMStr:%@",  
self.cpMStr);

    

    NSLog(@"\n");

    

    

    

    str =@"我走了";//[[NSStringalloc]
initWithFormat:@"我走了"];//两种方式都一样

    

    

    

    NSLog(@"retainStr:%@", 
self.retainStr);

    

    NSLog(@"copyStr:%@",   
self.cpStr);

    

    NSLog(@"retainMStr:%@",
self.retainMStr);

    

    NSLog(@"copyMStr:%@",  
self.cpMStr);

    

    NSLog(@"\n");

结果：

2016-04-07 17:39:00.780 FMDBTest[1305:504297] retainStr:我没变

2016-04-07 17:39:00.780 FMDBTest[1305:504297] copyStr:我没变

2016-04-07 17:39:00.780 FMDBTest[1305:504297] retainMStr:我没变

2016-04-07 17:39:00.780 FMDBTest[1305:504297] copyMStr:我没变

2016-04-07 17:39:00.780 FMDBTest[1305:504297] 

2016-04-07 17:39:00.780 FMDBTest[1305:504297] retainStr:我变了

2016-04-07 17:39:00.780 FMDBTest[1305:504297] copyStr:我没变

2016-04-07 17:39:00.781 FMDBTest[1305:504297] retainMStr:我变了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] copyMStr:我没变

2016-04-07 17:39:00.781 FMDBTest[1305:504297] 

2016-04-07 17:39:00.781 FMDBTest[1305:504297] retainStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] copyStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] retainMStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] copyMStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] 

2016-04-07 17:39:00.781 FMDBTest[1305:504297] retainStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] copyStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] retainMStr:我来了

2016-04-07 17:39:00.781 FMDBTest[1305:504297] copyMStr:我来了

2016-04-07 17:39:00.782 FMDBTest[1305:504297]