C++ 链表插入 运行时错误

Question

void push_front (const T &newItem)
{
Node *newHead = new Node;
newHead -> item = newItem;
newHead -> next = head;
head = newHead;
} // push_front

void pop_front ()
{
Node *oldHead = head;
head = head->next ;
delete oldHead;
}// pop_front

void push_back (const T &newItem )
{
Node *newNode = new Node;
newNode->item = newItem;
Node *middleNode = head;
while( middleNode->next != NULL)
{
middleNode = middleNode ->next ;
}
middleNode->next = newNode;
}

void pob_back()
{
Node *middleNode = head;
Node *middleNode_next = middleNode->next ;
while(middleNode_next->next != NULL)
{
middleNode = middleNode->next ;
middleNode_next = middleNode->next ;
}
middleNode->next = NULL:
delete middleNode_next;
}

该头文件的一部分 用来在一个单向链表中插入和删除头尾节点 并进行一个时间复杂度的实验 .cpp 文件中的一部分如下

cin >> n;
start_time = clock();
for (int i = 0; i < n; i++)
myLinked.push_front (i);
// Calculate how long the task took:
finish_time = clock();
elapsed_time = finish_time - start_time;
cout << "front_push"<<elapsed_time<<endl;

start_time = clock();
for (int i = 0; i < n; i++)
myLinked.push_back (i);
// Calculate how long the task took:
finish_time = clock();
elapsed_time = finish_time - start_time;
cout << "front_back << elapsed_time << endl;

编译能够通过 但是运行时出现问题 而且只有在尾部插入时才会有问题 我猜好像是那个循环有问题 但具体不知道怎么解决 请哪位帮帮忙 谢谢了

Answer 1

head要初始化为NULL。当head为NULL时，push_back，pop_front，pop_back会出错。其他的没看出来什么问题。