I made a test for NSString.

```
int a = 10;
NSString *str1 = @"str";
NSString *str2 = [NSString stringWithFormat:@"str"];
NSString *str3 = @"str";
NSString *str4 = @"str2";
NSLog(@"%p %p | 3 %p | 4 %p | a %p", str1,str2,str3,str4,&a);

```

result is

```
0x1286287c8 0xa000000007274733 | 3 0x1286287c8 | 4 0x1286287e8 | a 0x7ffeeb215b14

```

this test placed in iPhone 6s(11.1) Simulator. So what's the place of `str1` in memory? is it Stack or Heap?