关于C结构体内存管理的查询

发布于 2025-01-19 10:25:02 字数 422 浏览 4 评论 0原文

假设有一个结构体 a 和其他结构体作为成员

struct a {
struct b* b;
struct c* c;
};
struct a* a1;

现在我动态分配内存给 a 的对象 a1 = (struct a*) malloc(sizeof(a));

现在我同样创建了 struct b 的新对象 struct b* b1 = (struct b*) malloc(sizeof(b));

现在，在代码中一段时间后，我在 a1 中创建了 b1 的引用。

a1.b = b1;
b1 = NULL;

稍后，如果我释放 a1，分配的内存是否会分配给 a1？ b1也被释放了？ 免费（a1）；

原文

Suppose there is a struct a with other structs as members

struct a {
struct b* b;
struct c* c;
};
struct a* a1;

Now I allocate memory dynamically to an object of a
a1 = (struct a*) malloc(sizeof(a));

Now I similarly create a new object of struct b
struct b* b1 = (struct b*) malloc(sizeof(b));

Now after some time in code I create a reference for b1 in a1

a1.b = b1;
b1 = NULL;

Later if I free a1, will the memory allocated to b1 also get freed?
free(a1);

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南渊 2025-01-26 10:25:02

稍后，如果我释放A1，将分配给B1的内存也会被释放

则不会。规则非常简单：

每个恰好一个 malloc（假设我们确实要自由记忆）
传递给free的地址必须完全是以前的malloc返回的内容。

这里malloc当然也适用于任何其他分配功能，例如calloc，realloc等调用是：

free(a1.b);
free(a1);

Later if I free a1, will the memory allocated to b1 also get freed

No it will not. The rules are very simple:

Exactly one free for each malloc (assuming we do want to free memory)
The address passed to free must be exactly what was returned by a previous malloc.

Here malloc of course applies also to any other allocation function such as calloc, realloc, etc. So in your example the required free calls are: