NSArray的大小 [英] Size of NSArray

问题描述

当我试图检查声明没有任何容量的NSArray的大小时，我发现它4.现在问题是为什么它总是4？请帮我找到它....
谢谢

When I tried to check the size of NSArray which is declared without any capacity, I found it 4. Now the question is why it is always 4? please help me out to find it.... Thanks

推荐答案

鉴于此：

NSArray *foo;
NSLog(@"%d", sizeof(foo));

您将获得4或8，具体取决于您使用的是32位还是64位系统。请注意，我非常有目的地没有初始化 foo ;没有必要这样做 sizeof（foo）给 foo 和 foo 只是指向对象的随机指针。如果那是 id foo就没关系;无效* foo的; NSString * foo; all都是4或8.

You'll either get 4 or 8, depending on if you are on a 32 or 64 bit system. Note that I quite purposefully didn't initialize foo; there is no need to do so as sizeof(foo) is giving the bytesize of foo and foo is just a random pointer to an object. Wouldn't matter if that were id foo; void*foo; NSString*foo; all would be 4 or 8.

如果你想要特定类的实例的分配大小，那么Objective- C运行时提供了可以完全实现的内省API。但是，我真的没有想到为什么这会比程序中的有趣更多。

If you want the allocated size of an instance of a particular class, the Objective-C runtime provides introspection API that can do exactly that. However, I can't really think of any reason why that would be more than passingly interesting in a program.

请注意，实例的分配大小不会占用任何子分配。即NSArray可能有一个支持商店，这是一个单独的分配。

Note that the allocation size of an instance does not account for any sub-allocations. I.e. an NSArray likely has a backing store which is a separate allocation.

重申：

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