What is the use of null pointer in C++?

Null pointer in C++ represents a pointer that does not point to valid memory. It is usually assigned a nullptr value. Its usage includes initializing an unallocated pointer, serving as a sentinel value for loop or linked list traversal, and indicating the release or invalid memory. The advantages are improved code readability, prevention of null pointer dereference errors, and dynamic memory management. In the actual case, a null pointer is used to traverse the linked list, and the nullptr sentinel value is used to terminate the traversal.

Usage of null pointer in C++

The null pointer plays a vital role in C++ and is used to represent Pointer not pointing to any valid memory address. They are usually assigned the special value nullptr, which is a C++ keyword defined in the 939b761e2bf861db83e881d55896f840 header file.

Usage

Null pointers can be used to represent various situations:

• Initialize a pointer variable that has not allocated memory.
• As a sentinel value to terminate a loop or linked list traversal.
• When the memory pointed to by the pointer has been released or is no longer valid.

Advantages

Using null pointers has the following advantages:

• Increases the readability and maintainability of the code.
• Helps detect and prevent null pointer dereference errors.
• Allows dynamic memory management and resource release.

Practical case

Suppose we have a linked list that stores integers:

struct Node {
  int data;
  Node* next;
};

We can use a null pointer to traverse the linked list, as follows Shown:

Node* head = nullptr;  // 初始化头指针为空指针

// 添加一些节点到链表
Node* node1 = new Node{1, nullptr};
Node* node2 = new Node{2, nullptr};
node1->next = node2;
head = node1;  // 更新头指针

// 遍历链表，使用空指针作为哨兵值
Node* curr = head;
while (curr != nullptr) {
  cout << curr->data << endl;
  curr = curr->next;
}

End

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