运行-时间的三指针异常规则（Graph-Node）

Question

问题描述

我正在尝试为图表编写 class 节点。每个节点由 :

表示

ID
距离
父节点

我编写了以下三个函数：

Node(const Node &);
Node & operator=(const Node & );
~Node();

我将父节点分配给现有节点的那一刻。在运行的时候我得到了一个巨大的异常。幸好我没有炸毁电脑。我是否正确编码了以下三个函数？

我删除了distance和id的getter和setter函数以缩短代码。

谢谢。

Node.h

#ifndef NODE_H
#define NODE_H

class Node{
    public:
        Node(int);
        //rule of three
        Node(const Node &);
        Node & operator=(const Node & );
        ~Node();
        
        //getters and setters
        int getId() const;
        int getDistance() const;
        Node* getParent() const;
        
        void setParent(Node *);
        void setDistance(int);
    private:
        int _distance;
        int _id;
        Node * _parent;
};

#endif

node.cpp

#include "node.h"

Node::Node(int id):_id(id),_distance(INT_MAX),_parent(nullptr){}

Node::Node(const Node & other):_distance(other.getDistance()),_parent(nullptr){
    cout << "copy constructor " << endl;
     _parent = new Node(other.getId());
     if(other.getParent() != nullptr){
        _parent->setParent(other.getParent());
     }
}

Node::~Node(){
    cout <<"destructor" << endl;
    if(_parent != nullptr)
        delete _parent;
}
Node & Node::operator=(const Node& other){
    cout << "assignment " << endl;
    //self reference
    if(this == &other){
        return *this;
    }

    if(other.getParent() != nullptr){
        _parent->setParent(other.getParent());
     }
   _id = other.getId();
   _distance = other.getDistance();
    
    return *this;
}

Node* Node::getParent() const{
    return _parent;
}

int Node::getId() const{
    return _id;  
}

void Node::setParent(Node * parent){
    _parent = parent;
}

问题

总的来说一切顺利:

    Node n0(0); 
    Node n1(1);
    Node n2(2); 
    Node n3(3); 
    
   // constructor(n0);
    Node n4 = n0;
    cout << n4.getParent() << endl;
    cout << n0.getParent() << endl;

直到我这样做：

====>n3.setParent(&n4);<======。在运行时，我得到以下信息：

*** Error in `./graph': free(): invalid pointer: 0x00007ffecf36b250 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x777e5)[0x7fd4b50637e5]
/lib/x86_64-linux-gnu/libc.so.6(+0x7fe0a)[0x7fd4b506be0a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7fd4b506f98c]
./graph[0x401007]
./graph[0x406128]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fd4b500c830]
./graph[0x400df9]
======= Memory map: ========
00400000-0040a000 r-xp 00000000 08:08 1442084                            /home/hani/Documents/dataStructurecplusplus/graph/graph
00609000-0060a000 r--p 00009000 08:08 1442084                            /home/hani/Documents/dataStructurecplusplus/graph/graph
0060a000-0060b000 rw-p 0000a000 08:08 1442084                            /home/hani/Documents/dataStructurecplusplus/graph/graph
009f1000-00a23000 rw-p 00000000 00:00 0                                  [heap]
7fd4b0000000-7fd4b0021000 rw-p 00000000 00:00 0 
7fd4b0021000-7fd4b4000000 ---p 00000000 00:00 0 
7fd4b4cdc000-7fd4b4de4000 r-xp 00000000 08:08 3932346                    /lib/x86_64-linux-gnu/libm-2.23.so
7fd4b4de4000-7fd4b4fe3000 ---p 00108000 08:08 3932346                    /lib/x86_64-linux-gnu/libm-2.23.so
7fd4b4fe3000-7fd4b4fe4000 r--p 00107000 08:08 3932346                    /lib/x86_64-linux-gnu/libm-2.23.so
7fd4b4fe4000-7fd4b4fe5000 rw-p 00108000 08:08 3932346                    /lib/x86_64-linux-gnu/libm-2.23.so
7fd4b4fec000-7fd4b51ab000 r-xp 00000000 08:08 3932341                    /lib/x86_64-linux-gnu/libc-2.23.so
7fd4b51ab000-7fd4b53ab000 ---p 001bf000 08:08 3932341                    /lib/x86_64-linux-gnu/libc-2.23.so
7fd4b53ab000-7fd4b53af000 r--p 001bf000 08:08 3932341                    /lib/x86_64-linux-gnu/libc-2.23.so
7fd4b53af000-7fd4b53b1000 rw-p 001c3000 08:08 3932341                    /lib/x86_64-linux-gnu/libc-2.23.so
7fd4b53b1000-7fd4b53b5000 rw-p 00000000 00:00 0 
7fd4b53bc000-7fd4b53d2000 r-xp 00000000 08:08 3936718                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd4b53d2000-7fd4b55d1000 ---p 00016000 08:08 3936718                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd4b55d1000-7fd4b55d2000 rw-p 00015000 08:08 3936718                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7fd4b55d4000-7fd4b5746000 r-xp 00000000 08:08 7211138                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7fd4b5746000-7fd4b5946000 ---p 00172000 08:08 7211138                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7fd4b5946000-7fd4b5950000 r--p 00172000 08:08 7211138                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7fd4b5950000-7fd4b5952000 rw-p 0017c000 08:08 7211138                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7fd4b5952000-7fd4b5956000 rw-p 00000000 00:00 0 
7fd4b595c000-7fd4b5982000 r-xp 00000000 08:08 3932330                    /lib/x86_64-linux-gnu/ld-2.23.so
7fd4b5b80000-7fd4b5b81000 rw-p 00000000 00:00 0 
7fd4b5b81000-7fd4b5b82000 r--p 00025000 08:08 3932330                    /lib/x86_64-linux-gnu/ld-2.23.so
7fd4b5b82000-7fd4b5b83000 rw-p 00026000 08:08 3932330                    /lib/x86_64-linux-gnu/ld-2.23.so
7fd4b5b83000-7fd4b5b85000 rw-p 00000000 00:00 0 
7fd4b5b85000-7fd4b5b8b000 rw-p 00000000 00:00 0 
7ffecf34c000-7ffecf36d000 rw-p 00000000 00:00 0                          [stack]
7ffecf3bc000-7ffecf3be000 r--p 00000000 00:00 0                          [vvar]
7ffecf3be000-7ffecf3c0000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]

Answer 1

问题不是n3.setParent(&n4)引起的；您可以通过添加 {char c; cin >> c;} 在此语句之后，main() 结束之前。

问题是if (_parent != nullptr) delete _parent;

节点n0-n4是在main()的栈上创建的，所以当main()结束时会被删除。但是，其中一个节点已经被析构函数中的 delete 语句删除，这给了你 free(): invalid pointer: 0x00007ffecf36b250 error.

对使用 new 创建的对象使用 delete。

运行-时间的三指针异常规则（Graph-Node）

Rule of three pointer exception at run-time (Graph-Node)

c++

graph

operator-overloading

destructor

copy-constructor

问题描述

Node.h

node.cpp

问题