是否有必要在 free() 之前检查指针是否为空

Question

Ì 用于确保指针在释放之前不为空，所以我通常会像这样销毁动态创建的结构：

Node *destroy_node(Node *node) {
    if (node) {
        free(node);
    }
    return NULL;
}

但是CERT MEM34建议因为 free() 接受空指针，我也可以写

Node *destroy_node(Node *node) {
    free(node);
    return NULL;
}

对吗？

Answer 1

是的，将 NULL（空指针常量）传递给 free() 是完全有效的。

引用 C11，章节 §7.22.3.3，（强调我的）

The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. [...]

Answer 2

是的，将 NULL 传递给 free 是空操作。

摘自n1570（C11终稿）：

7.22.3.3 The free function Synopsis
1 #include void free(void *ptr);
Description
2 The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by a memory management function, or if the space has been deallocated by a call to free or realloc, the behavior is undeﬁned.
Returns
3 The free function returns no value.

是否有必要在 free() 之前检查指针是否为空

Is it necessary to check whether a pointer is null before free()

c

free

struct

pointers

memory-management