C ++如何在不丢失内存的情况下删除节点？

Question

我只是无法让这个单链表在不丢失记忆的情况下工作。我已经用谷歌搜索了，据我所知，我做了最建议的事情。我也尝试过“free(deleteNode)”而不是“delete deleteNode”。有人认为他们知道答案吗？

提前谢谢你。

我正在尝试使用此代码插入和删除-p

List l{};
l.insert(5);
l.remove(5);

我敢打赌错误出在我的remove 函数中：

void List::remove(int input){

    if(top -> getValue() == input){
        Node * deleteNode = new Node;
        deleteNode = top;
        top = top -> getNext();
        delete deleteNode;
        amount--;
        return;
    }

    Node * tmpNode;
    tmpNode = new Node(top);

    while(tmpNode -> getValue() != 0){
        if(tmpNode -> getNext() -> getValue() == input){
            Node * deleteNode;
            deleteNode = new Node(tmpNode -> getNext());
            tmpNode -> setNext(deleteNode -> getNext());
            deleteNode -> setNext(nullptr);
            delete deleteNode;
            amount--;
            return;
        }
        tmpNode = tmpNode -> getNext();
    }
}

我的抄送文件：

#include <cstddef>
using namespace std;
#include "List.h"
#include <iostream>

List::List() : amount(0), top(nullptr) {
}

List::List(Node* input) : List(){
    top = input;
}

List::~List(){//destructor
    while( top != nullptr){
        remove( top -> getValue());
    }
}

List::Node::~Node(){//destructor
    next = nullptr;
    //this =NULL;
}

    List::List(List const& other) : List(){
        *this = other;
    }

    List::List(List && other) : List(){ // move constructor
       Node* tmpNode = other.top;
       other.top = top;
       top = tmpNode;
       int tmpAmount = size();
        setSize(other.size());
        other.setSize(tmpAmount);
    }

    List & List::operator=(List && other){ // move assignment
        Node* tmpNode = other.top;
        other.top = top;
        top = tmpNode;
        int tmpAmount = size();
        other.size();
        setSize(other.size());
        other.setSize(tmpAmount);
        return *this;
    }

    List & List::operator=(List const& other){// copy assignment
        Node * tmpNode; 
        tmpNode = other.top;

        while(tmpNode != nullptr){
            insert(tmpNode -> getValue());
            tmpNode = tmpNode -> getNext();
        }

        return *this;
    }

void List::setSize(int input){
    amount = input;
}

void List::insert(int input){
    Node* newNode;
    newNode = new Node(input);
    if(!top){
        top = newNode;
        amount++;
        return;
    }

    if(input > top -> getValue()){
        newNode -> setNext(top);
        top = newNode;
        amount++;
        return;
    }

    top -> putIterator(newNode);
    amount++;
    return;
}

string List::print(){
    if(top == nullptr){
        return "";
    }
    string output = to_string(top -> getValue());
    if(top -> getNext() == nullptr){
        return output;
    }
    return top -> getNext() -> print(output);
}

void List::remove(int input){

    if(top -> getValue() == input){
        Node * deleteNode = new Node;
        deleteNode = top;
        top = top -> getNext();
        delete deleteNode;
        amount--;
        return;
    }

    Node * tmpNode;
    tmpNode = new Node(top);

    while(tmpNode -> getValue() != 0){
        if(tmpNode -> getNext() -> getValue() == input){
            Node * deleteNode;
            deleteNode = new Node(tmpNode -> getNext());
            tmpNode -> setNext(deleteNode -> getNext());
            deleteNode -> setNext(nullptr);
            delete deleteNode;
            amount--;
            return;
        }
        tmpNode = tmpNode -> getNext();
    }
}

List::Node List::find(int input){
    return iterate(input).getNext();
}

List::Node List::iterate(int input){
    return top -> iterate(input);
}

bool List::isEmpty(){
    if(size()==0){
        return true;
    }
    return false;
}

int List::size(){
    return amount;
}

List::Node::Node(int input, Node &nextInput){
    value = input;
    next = &nextInput;
}

List::Node::Node(int input){
    value = input;
    next = nullptr;
}

List::Node::Node(const Node* input){
    *this = *input;
}

List::Node* List::Node::getNext(){
    return next;
}

void List::Node::setNext(Node* input){
    next = input;
}

int List::Node::getValue(){
    return value;
}

/*
void List::Node::deleteNode(){
    delete *this;
}*/

void List::Node::putIterator(Node* newNode){
    if (next == nullptr){
        next = newNode;
        next -> setNext(nullptr);
        return;
    }

    if(getValue() == newNode -> getValue()){
        newNode -> setNext(getNext());
        setNext(newNode);
        return; 
    }

    if(next -> value < newNode -> value && value > newNode -> value){
        newNode -> setNext(getNext());
        setNext(newNode);
        return;
    }

    next -> putIterator(newNode);
    return;
}

string List::Node::print(string input){
    input = input + ", " + to_string(value);
    if(next == nullptr){
        return input;
    }
    return next -> print(input);
}

List::Node List::Node::iterate(int input){
    if (next -> value==input){
        return *this;
    }
    if (next -> value==0){
        return nullptr;
    }

    return next ->iterate(input);
}

bool List::Node::operator!() const{
    if(value == 0){
        return true;
    }
    return false;
}

我的头文件：

#ifndef _LIST_H_
#define _LIST_H_
#include <string>

class List
{
  public:
    List();

    ~List(); //destructor
    List(List const &other);
    List(List &&other);                 // move constructor
    List &operator=(List &&other);      // move assignment
    List &operator=(List const &other); // copy assignment

  class Node
    {
      public:
        Node() = default;
        ~Node();
        Node(int input, Node &nextInput);
        Node(int input);
        Node(const Node *input);
        Node *getNext();
        void setNext(Node *input);
        int getValue();
        Node iterate(int input);
        void putIterator(Node *newNode);
        void deleteNode();
        bool operator!() const;
        std::string print(std::string input);

      private:
        int value;
        Node *next;
    };

    List(Node* input);
    void insert(int input);
    void remove(int input);
    Node iterate(int input);
    int size();
    bool isEmpty();
    Node find(int input);
    std::string print();
    void setSize(int input);

   private:

    Node *top;
    int amount;
};

#endif

Answer 1

你为什么要在remove()中创建一个新节点呢？

接下来，将 getter、setter 和所有其他废话添加到 Node（这是 List 的实现细节）只会使 List 复杂化。将其全部删除（也许除了 ctor）。

考虑使用双重间接或其他方式来消除特殊情况和由此产生的容易出错的重复：

void List::remove(int x) {
    auto p = ⊤
    while (*p && p[0]->value != x)
        p = &p[0]->next;
    if (*p)
        delete std::exchange(*p, p[0]->next);
}

替代方案：

void List::remove(int x) {
    auto curr = top;
    curr = nullptr;
    auto next = top;
    while (next && next->value != x) {
        curr = next;
        next = next->next;
    }
    if (!next)
        return;
    (curr ? curr->next : top) = next->next;
    delete next;
}

Answer 2

您正在调用新的构造函数，然后设置指针，这会造成内存丢失。

Node * deleteNode = new Node;

为您不想要的新节点分配内存。这是您的内存泄漏发生的地方，因为您将 设置为新地址而导致旧内存泄漏。

New的作用是分配堆内存，所以只有在你选择分配更多内存时才调用它。

非常简单的解决方案是在声明对象时不要调用 new。尝试类似：

void List::remove(int input){

    if(top -> getValue() == input){
        Node * deleteNode;
        deleteNode = top;
        top = top -> getNext();
        delete deleteNode;
        amount--;
        return;
    }

    Node * tmpNode;
    tmpNode = top;

    while(tmpNode -> getValue() != 0){
        if(tmpNode -> getNext() -> getValue() == input){
            Node * deleteNode;
            deleteNode = tmpNode -> getNext());
            tmpNode -> setNext(deleteNode -> getNext());
            deleteNode -> setNext(nullptr); // you could probably delete this line
            delete deleteNode;
            amount--;
            return;
        }
        tmpNode = tmpNode -> getNext();
    }

}