动态内存分配的变量使用指针复制给另一个变量如何释放

问题:
使用new申请了一块空间,然后使用指针给另一个变量,那么该delete哪个变量?

测试代码:(代码来源百度,然后我发现没有delete释放new对象)

cout << "****进行排序****" << endl;
//第一位地址可以存放指示器,从第二位开始保存数据
node *mylist = new node[sizeof(node)];
mylist->data = 0;
mylist->next = NULL;

int len = length(head);
int i = 0;
node * cur = mylist;


node *headcopy = head;
while (len--)
{
    //node * newNode = (node *)malloc(sizeof(node));   
    node *newNode = new node[sizeof(node)];            
    newNode->data = headcopy->data;
    newNode->next = NULL;
    cur->next = newNode;
    cur = cur->next;
    headcopy=headcopy->next;
}
head = insertSort(mylist);
head = del(head, 0);
printL(head);

return 0;

}

我百度看到这么一串代码,原代码是没有写delete的,我私自认为有内存泄露,就自己尝试加上了delete,但是delete newNode这个是没有问题的,但是再delete mylist时,VS提示错误。

因为考虑循环内部的new对象无法delete(对于局部变量,要在所在的模块中delete),于是自己将newNode写在了循环体外。

代码:

cout << "****进行排序****" << endl;
//第一位地址可以存放指示器,从第二位开始保存数据
node *mylist = new node[sizeof(node)];
mylist->data = 0;
mylist->next = NULL;

int len = length(head);
int i = 0;
node * cur = mylist;


node *headcopy = head;
node *newNode = new node[0];
while (len--)
{
    //node * newNode = (node *)malloc(sizeof(node));   
    newNode = new node[sizeof(node)];
    newNode->data = headcopy->data;
    newNode->next = NULL;
    cur->next = newNode;
    cur = cur->next;
    headcopy = headcopy->next;
}
head = insertSort(mylist);
head = del(head, 0);
printL(head);


if (newNode)
    delete[] newNode;

if(mylist)
    delete[] mylist;

return 0;

}

clipboard.png

附加:
1.如果觉得不好解释请直接添加代码解决方案,我在摸索一下。
2.关于new动态内存分配,我记得之前也看过不要使用指针复制之类的,再去百度找不到了,需要注意容易引起内存泄露的情况也请各位解释一下。(PS:当然使用智能指针比较好,但就怕有的版本不支持嘛QAQ)

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    2 个回答
    • 39
    #include <iostream>
    #include <stdio.h>
    #include <string>
    #include <conio.h>
    
    /**
    * cstdio是将stdio.h的内容用C++头文件的形式表示出来。
    *stdio.h是C标准函数库中的头文件,即:standard buffered input&output。
    *提供基本的文字的输入输出流操作(包括屏幕和文件等)。
    */
    
    /**
    *conio是Console Input/Output(控制台输入输出)的简写,其中定义了通过控制台进行数据输入和数据输出的函数,
    *主要是一些用户通过按键盘产生的对应操作,比如getch()()函数等等。
    */
    
    using namespace std;
    
    struct node
    {
        int data;
        node *next;
    };
    typedef struct node node, *list;
    
    // 创建单链表
    node *creat()
    {
        node *head, *p;
        head = new node;
        p = head;
    
        int x, cycle = 1;
        while (cycle)
        {
            cout << "Please input the data for single linker : ";
            cin >> x;
    
            if (x != 0)
            {
                node *s = new node;
                s->data = x;
                cout << "Input data : " << x << endl;
    
                p->next = s;
                p = s;
            }
            else
            {
                cycle = 0;
                cout << "Input done! " << endl;
            }
        }
    
        head = head->next;
        p->next = NULL;
        //cout << "\nFirst data of single linker is " << head->data << endl;
    
        return head;
    }
    
    // 单链表测长
    int length(node *head)
    {
        int n = 0;
        node *p = head;
    
        while (p != NULL)
        {
            p = p->next;
            n++;
        }
    
        return n;
    }
    
    // 单链表打印
    void printL(node *head)
    {
        node *p = head;
    
        while (p != NULL)
        {
            cout << "Single Linker data is " << p->data << endl;
            p = p->next;
        }
    }
    
    // 单链表插入
    node *insert(node *head, int num)
    {
        node *p0, *p1, *p2;
        p1 = head;
    
        p2 = new node;
        p0 = new node; // 插入节点
        p0->data = num;// 插入数据
    
        while (p0->data > p1->data && p1->next != NULL)
        {
            p2 = p1;
            p1 = p1->next;// p0,p1和p2位置: p2->p1->p0
        }
    
        if (p0->data <= p1->data)
        {
            if (p1 == head)
            {// 头部前段插入 p0和p1位置: p0->p1->...
                head = p0;
                p0->next = p1;
            }
            else
            {// 插入中间节点 p0,p1和p2位置: p2-> p0 -> p1
                p2->next = p0;
                p0->next = p1;
            }
        }
        else
        {   // 尾部插入节点 p0,p1和p2位置: p2->p1->p0->NULL
            p1->next = p0;
            p0->next = NULL;
        }
        return head;
    }
    
    // 单链表删除
    node *del(node *head, int num)
    {
        node *p1, *p2;
        p2 = new node;
        p1 = head;
    
        while (num != p1->data && p1->next != NULL)
        {
            p2 = p1;
            p1 = p1->next;// p1和p2位置: p2->p1        
        }
    
        if (num == p1->data)
        {
            if (p1 == head)// 删除头节点
            {
                head = p1->next;
                delete p1;
            }
            else
            {
                p2->next = p1->next;
                delete p1;
            }
        }
        else
        {
            cout << num << " could not been found in the current single linker!" << endl;
        }
        return head;
    }
    
    //=============插入排序====================
    node *insertSort(node *head)
    {
        node  *p1, *prep1, *p2, *prep2, *temp;
        prep1 = head->next;
        p1 = prep1->next;
        //prep1和p1是否需要手动后移
        bool flag;
    
        while (p1 != NULL)
        {
            flag = true;
            temp = p1;
            //由于是单向链表,所以只能从头部开始检索
            for (prep2 = head, p2 = head->next; p2 != p1; prep2 = prep2->next, p2 = p2->next)
            {
                //发现第一个较大值
                if (p2->data > p1->data)
                {
                    p1 = p1->next;
                    prep1->next = p1;
                    prep2->next = temp;
                    temp->next = p2;
                    flag = false;
                    break;
                }
            }
            //手动后移prep1和p1
            if (flag)
            {
                prep1 = prep1->next;
                p1 = p1->next;
            }
        }
        return head;
    }
    
    int main()
    {
        cout << "***创建单链表***" << endl;
        node *head = creat();
        cout << endl;
    
        cout << "***计算链表长***" << endl;
        int n = length(head);
        cout << "The length of input single linker is " << n << "." << endl;
        cout << endl;
    
        cout << "***打印单链表***" << endl;
        printL(head);
        cout << endl;
    
        cout << "****插入节点****" << endl;
        cout << "Please input the data for inserting operate : ";
        int inData;
        cin >> inData;
        head = insert(head, inData);
        printL(head);
        cout << endl;
    
        cout << "****删除节点****" << endl;
        cout << "Please input the data for deleting operate : ";
        int outData;
        cin >> outData;
        head = del(head, outData);
        printL(head);
        cout << endl;
    
        cout << "****进行排序****" << endl;
        //第一位地址可以存放指示器,从第二位开始保存数据
        node *mylist = new node[sizeof(node)];
        mylist->data = 0;
        mylist->next = NULL;
    
        int len = length(head);
        int i = 0;
        node * cur = mylist;
    
    
        node *headcopy = head;
        //node *newNode = new node[0];
        while (len--)
        {
            //node * newNode = (node *)malloc(sizeof(node));   
            node * newNode = new node;
            newNode->data = headcopy->data;
            newNode->next = NULL;
            cur->next = newNode;
            cur = cur->next;
            headcopy = headcopy->next;
        }
        head = insertSort(mylist);
        head = del(head, 0);
        printL(head);
    
    
        //if (newNode)
        //    delete[] newNode;
    
        //if(mylist)
        //    delete[] mylist;
    
        while (mylist != NULL) {
            node *t = mylist->next;
            delete mylist;
            mylist = t;
        }
    
        return 0;
    }
    

    这是我的完整代码。麻烦你看一下。QAQ

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