是在栈上还是堆上？

发布于 2024-07-25 05:49:11 字数 628 浏览 3 评论 0原文

我有一些令人困惑的 C 代码。由于与此代码有关的原因，我想知道如何判断 struct 对象最终位于堆还是堆栈上？

这些对象是 不是使用 malloc 或 calloc 创建的。它们以数组的形式开始它们的生命。出于本文的目的，我将将该结构称为 Emp。

Emp myEmp[6];

/* Each myEmp[?] item is populated in code */

对象以各种方式排序和操作，在某些时候，对象被复制然后传递给数组指针。复制是通过memcpy完成的。然后将对象放入类似：Emp* emps_a[6] 中。

这些对象来自副本并分配给上面的 emps_a。

int i;
for( i = 0; i < n; i++ )
{
    emps_a[i] = myEmpsCopy + i;
}

我不确定这是否与我的问题有关。我从不需要 free() 或进行内存清理...恐怕我对 C 不太了解。

非常感谢您的帮助。

原文

I have some C code that is something of a puzzle. For a reason to do with this code, I'm wondering how I can tell if a struct object is ending up on the heap or stack?

The objects are not being created with malloc or calloc. They start their life in the form of an array. For the purposes of this post, I'm going to call the struct Emp.

Emp myEmp[6];

/* Each myEmp[?] item is populated in code */

The objects are sorted and manipulated in various ways and at some point, the objects are copied and then handed to a array-pointer. The copy is done via memcpy. The objects are then put in to something like: Emp* emps_a[6].

The objects go from a copy and are assigned in to the above emps_a.

int i;
for( i = 0; i < n; i++ )
{
    emps_a[i] = myEmpsCopy + i;
}

I'm not sure if some or any of this has bearing on my question. I never need free() or do memory clean up... I'm afraid I don't know too much about C.

The help is greatly appreciated.

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╰沐子 2024-08-01 05:49:11

除了使用 static 修饰符声明的全局变量和变量（分配在单独的内存区域中）之外，在函数体中声明的局部变量都在堆栈上分配，而无论您调用 malloc for 分配在堆上。此外，C99 可变大小的数组和使用 _alloca 分配的内存最终将位于堆栈上。

int* x[10];   // The addresses are held on the stack
int i;        // On the stack
for(i = 0; i < 10; ++i)
   x[i] = malloc(sizeof(int)*10);  // Allocates memory on the heap

例如，在上面的代码中，堆栈上有一个 int* 值数组，保存堆中 10 个不同位置的地址。

Leaving global variables and variables declared with static modifier (which are allocated in a separate memory region) aside, local variables declared in a function body are allocated on the stack whereas whatever you call malloc for is allocated on the heap. Also, C99 variable sized arrays and memory allocated with _alloca will end up on stack.

int* x[10];   // The addresses are held on the stack
int i;        // On the stack
for(i = 0; i < 10; ++i)
   x[i] = malloc(sizeof(int)*10);  // Allocates memory on the heap

For example, in the above code, there's an array of int* values on the stack holding addresses to 10 different locations in the heap.

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