while ((nextPoint = getNext()) != null)
时间: 2024-02-12 22:03:19 浏览: 33
这是一个while循环语句,其条件表达式为"(nextPoint = getNext()) != null",其中getNext()是一个方法调用,该方法返回一个值,该值被赋值给nextPoint变量。该循环语句的含义是:当getNext()方法返回的值不为null时,执行循环体内的语句。在循环体内,可以使用nextPoint变量来引用getNext()方法返回的值。
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CDemoDoc::~CDemoDoc() { if (m_pList != NULL) { for (POSITION pos = m_pList->GetHeadPosition(); pos != NULL; ) { CPanCtRgn* pRgn = (CPanCtRgn*) m_pList->GetNext(pos); if (pRgn != NULL) { delete pRgn; } } m_pList->RemoveAll(); delete m_pList; } }
这段代码是在 `CDemoDoc` 类的析构函数 `CDemoDoc::~CDemoDoc()` 中执行的。让我逐行解释:
- `if (m_pList != NULL)`:检查成员变量 `m_pList` 是否为空指针。
- `for (POSITION pos = m_pList->GetHeadPosition(); pos != NULL; )`:使用 `GetHeadPosition()` 函数获取链表的头部位置,并在每次迭代结束后更新 `pos`。
- `CPanCtRgn* pRgn = (CPanCtRgn*) m_pList->GetNext(pos);`:使用 `GetNext()` 函数获取链表中的下一个元素,并将其转换为 `CPanCtRgn*` 类型。
- `if (pRgn != NULL) { delete pRgn; }`:如果获取到有效的区域对象,则调用 `delete` 运算符释放该对象所占用的内存。
- `m_pList->RemoveAll();`:调用链表对象的 `RemoveAll()` 函数,移除所有的元素。
- `delete m_pList;`:最后,使用 `delete` 运算符释放链表对象所占用的内存。
这段代码的作用是在销毁 `CDemoDoc` 类的对象时,释放动态分配的资源。它首先遍历链表中的每个元素,将每个区域对象删除并释放内存。然后,它调用链表对象的 `RemoveAll()` 函数来移除所有元素,最后使用 `delete` 运算符释放链表对象的内存。这样做可以确保在销毁对象时,释放了与之关联的资源,避免内存泄漏。
检查代码并修改:class Node: def init(self, data): self.data = data self.prev = None self.next = None Class DoublyLinkedlist: # def init(self) self.head = None def remove(self,item): current = self.head previous = None found = False while not found: if current.getData() == item found = True else: previous = current current = current.getNext() if previous == None: self.head = current.getNext() current.prev = None else: previous.setNext(current.getNext()) current.prev = previous
class Node:
def __init__(self, data):
self.data = data
self.prev = None
self.next = None
class DoublyLinkedList: # 类名应该是DoublyLinkedList而不是DoublyLinkedlist
def __init__(self):
self.head = None
def append(self, data):
new_node = Node(data)
if self.head is None:
self.head = new_node
else:
current = self.head
while current.next is not None:
current = current.next
current.next = new_node
new_node.prev = current
def prepend(self, data):
new_node = Node(data)
if self.head is None:
self.head = new_node
else:
self.head.prev = new_node
new_node.next = self.head
self.head = new_node
def delete(self, data):
current = self.head
while current is not None:
if current.data == data:
if current.prev is not None:
current.prev.next = current.next
else:
self.head = current.next
if current.next is not None:
current.next.prev = current.prev
return
current = current.next
def print_list(self):
current = self.head
while current is not None:
print(current.data)
current = current.next