C语言结构体指针问题?报错

ubuntu15.04环境下报错：段错误

涉及函数代码：

void copyExp(struct elem **head, struct elem * from){
	struct elem * result = (struct elem*)malloc(sizeof(struct elem));
	result->c = from->c;
	result->n = from->n;
	result->next = NULL;
	(*head) = result;
	from = from->next;
	while(from != NULL){
		struct elem *p = (struct elem*)malloc(sizeof(struct elem));
		p->c = from->c;
		p->n = from->n;
		p->next = NULL;
		result->next = p;
		result = p;
		from = from->next;
	}
}

copyExp(&f[n+1], f[n]);	// 将f[n]的值赋值给f[n+1]

下面是我用gdb调试的错误信息：

Program received signal SIGSEGV, Segmentation fault.
0x00000000004010c6 in copyExp (head=0x7fffffffdbc8, from=0xf63d4e2e)
    at expression.c:31
31		result->c = from->c;
(gdb)