objective-C类是否在堆上存储基本类型属性？

Suppose I have a custom class:

假设我有一个自定义类：

@interface someClass : NSObject
@property (nonatomic, assign) int intProperty;
@end

and it has a method:

它有一个方法：

- (void)test {
    NSLog(@"%p", &(_intProperty));
}

Execute the following code:

执行以下代码：

SomeClass* someClass = [[SomeClass alloc] init];
someClass.intProperty = 3;
[someClass test];

The output is:

输出是：

2016-12-05 19:42:33.001951 test[2316:881536] 0x17401d078

Looks like an address on the heap. But as we know, you can't store a primitive type variable on the heap. So how does it read an int from a pointer to a heap address?

看起来像堆上的地址。但正如我们所知，您无法在堆上存储基本类型变量。那么它如何从指向堆地址的指针读取int？

Providing relevant links will be appreciated. Thanks in advance:)

提供相关链接将不胜感激。提前致谢：）

1 个解决方案

#1

When you call SomeClass alloc method, it allocates memory on the heap, the memory stores variables of SomeClass instance including intProperty.

当你调用SomeClass alloc方法时，它会在堆上分配内存，内存存储SomeClass实例的变量，包括intProperty。

We suppose you didn't use @synthesize to rename the instance variable of intProperty, so the backup variable of intProperty property is _intProperty.

我们假设您没有使用@synthesize重命名intProperty的实例变量，因此intProperty属性的备份变量是_intProperty。

someClass.intProperty = 3; this line of code stores 3 to the address of _intProperty. The compiler can figure out the address of _intProperty which is the address of someClass plus the a offset, the offset is the distance of the _intProperty variable address from the begin of someClass. As we know the address of _intProperty, we can read from it or write to it.

someClass.intProperty = 3;这行代码将3存储到_intProperty的地址。编译器可以找出_intProperty的地址，它是someClass的地址加上一个偏移量，偏移量是_intProperty变量地址与someClass开头的距离。我们知道_intProperty的地址，我们可以从中读取或写入它。

But as we know, you can't store a primitive type variable on the heap

但正如我们所知，您无法在堆上存储基本类型变量

It's wrong, we can store a primitive on heap, the code below store a integer value on the heap.

这是错误的，我们可以在堆上存储一个原语，下面的代码在堆上存储一个整数值。

int *a = (int *)malloc(sizeof(int)); // a is a pointer, its value is the address on the heap
*a = 4;  // store the value 4 to the address on the heap
free(a); // you must free the memory.

#1