What is CrtIsValidHeapPointer(pUserData)

[ahmed mahmoud]

I am new to C programming language
i am trying to implement linked list using C
but i found that error CrtIsValidHeapP ointer(pUserDat a)
i don't know what is it

my code

struct node
{
	int value;
	struct node * next;
};

void addNode(struct node * t)
{
	t->next = (struct node *)malloc(sizeof(struct node));
	if(t->next != NULL)
	{
		(t->next)->value = 5;
		(t->next)->next = NULL;
	}
	else
	{
	   printf("FATAL ERROR NO MEMORY");
	}
}


int main(array<System::String ^> ^args)
{
	struct node * p;
    struct node head;
	head.value = 1;
	head.next = NULL;
	p = & head;
       addNode(p);
	while(p != NULL)
	{
		printf("%d\n",(*p).value);
		p = (*p).next;
	}
	p = &head;
	free(p->next);
	p->next = NULL;
	free(p);
	p = NULL;
    return 0;
}

i know that there is lot of things that is not implemented efficiently but now i am focusing only on this error
thanks in advance

[Banfa]

You call free(p) but p has been set to &head and not malloced so you are trying to free memory that is not allocated on the heap and hence you get the error.