C++分段故障链表元素添加

Question

我在用C++编写链表实现时遇到了一个问题。每当我试图添加一个元素，我得到分段错误错误。

 #include <iostream>


    class node{
    public:
        int data;
        class node *next;
    };
    class LinkedList {
    public:
        node *head;
        LinkedList(int num);

        void add(int number);
        void display();
    };

    const int null = 0;
    LinkedList::LinkedList(int num) {
        // TODO Auto-generated constructor stub
        std::cout<<"Constructor Called"<<std::endl;
        head->data = num;
        head->next = null;
        std::cout<<"Constructor Call completed"<<std::endl;
    }



    void LinkedList::add(int num) {
        struct node *n=new node;
        n->data = num;
        n->next = null;
        struct node *current = head;
        while (current->next != null) {
            current = current->next;
        }
        current->next = n;
    }
    void LinkedList::display() {
        std::cout<<"Display"<<std::endl;
        struct node *current = head;

        while (current!= null) {
            std::cout << current->data << "->";
            current = current->next;
        }
        std::cout << "null"<<std::endl;
    }

    int main() {
        LinkedList l(1);
        l.display();
        l.add(2);
        l.display();
        return 0;
    }

提前感谢！

struct node *n=new node;

Constructor Called
Constructor Call completed

Breakpoint 1, main () at SampleCPP.cpp:60
60      l.display();
(gdb) s
LinkedList::display (this=0xbffff03c) at SampleCPP.cpp:48
48      std::cout
(gdb) n
51      while (current!= null) {
(gdb) n
52          std::cout data ";
(gdb) n
53          current = current->next;
(gdb) n
51      while (current!= null) {
(gdb) n
55      std::cout null
56  }
(gdb) n
main () at SampleCPP.cpp:61
61      l.add(2);
(gdb) s
LinkedList::add (this=0xbffff03c, num=2) at SampleCPP.cpp:38
38      struct node *n=new node;
(gdb) print n
$2 = (node *) 0x0
(gdb) 

Answer 1

您从不为head分配内存。那是你的问题.

在构造函数中分配它：

LinkedList::LinkedList(int num) {
    std::cout<<"Constructor Called"<<std::endl;
    head = new node; // This is missing!
    head->data = num;
    head->next = null;
    std::cout<<"Constructor Call completed"<<std::endl;
}

在程序完成之前释放所有的内存也是很好的…