如何在已经加载到双链表中的二进制文本中输入和删除节点？ C++

Question

我的代码是产品数据库的双链表，我可以选择输入产品、搜索、删除、修改、显示、保存（.bin）和上传（.bin） 在我使用加载二进制选项之前，所有选项都有效。 我的问题是，当我上传包含产品的 .bin 时，输入产品选项不起作用，并且当我想删除列表中的最后一个产品（所有其他选项都有效）时，删除产品不起作用。

这是输入一个产品代码：

void inP() {
    product* nuevo = new product();
    cout << "Ingrese el nombre del producto: ";
    cin >> nuevo->name;

    if (first == NULL) {
        first = nuevo;
        first->next = NULL;
        first->previous = NULL;
        last = first;
    }
    else {
        last->next = nuevo;
        nuevo->next = NULL;
        nuevo->previous = last;
        last = nuevo;
    }

    cout << "Producto agregado correctamente a la lista" << endl;
}

这是删除一个产品代码：

void deleteP() {

    product* current = new product();
    current = first;
    product* prev = new product();
    prev = NULL;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a eliminar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                cout << "\n" << current->name << " " << current->cant << " " << current->code << " " << current->marca << " " << current->descr << " " << current->monto << "\n";

                if (current == first) {
                    if (first->next == NULL) {
                        first = NULL;
                    }
                    else {
                        first = first->next;
                        first->previous = NULL;
                    }
                }
                else if (current == last) {
                    prev->next = NULL;
                    last = prev;
                }
                else {
                    prev->next = current->next;
                    current->next->previous = prev;
                
                }

                cout << "\n Producto Eliminado" << endl;
                found = true;
            }
            prev = current;
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

这是加载二进制代码：

void loadBin() {
    ifstream is(registryName, ios::in | ios::binary);
    product* reader;
    
    if (is.is_open()) {
        is.seekg(0, ios::end);
        int size = is.tellg();
        is.seekg(0, ios::beg);

        while (is.tellg() < size) {
            reader = new product;
            is.read((char*)reader, sizeof(product));
            reader->next = NULL;
            cout << reader->name << endl;
            
            if (first == NULL) {
                first = reader;
            }
            else {
                product* indice = first;
                while (indice->next != NULL) {
                    indice = indice->next;
                }
                indice->next = reader;
            }
        }
        is.close();
    }
}

以及所有代码：

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

string registryName = "products.bin";

struct product {
    string name;
    product* next;
    product* previous;
}*first, * last;

void inP();
void outP();
void searchP();
void modifyP();
void deleteP();
void saveBin();
void loadBin();

int main() {

    
    int op;
    do {
        system("CLS");
        cout << "Menu:" << endl;
        cout << "1. Input a Product " << endl;
        cout << "2. Show the list " << endl;
        cout << "3. Search a Product " << endl;
        cout << "4. Modify a product " << endl;
        cout << "5. Delete a product " << endl;
        cout << "6. Save List " << endl;
        cout << "7. Load Binary List " << endl;
        cout << "8. Exit" << endl;
        cin >> op;
        cout << "\n";

        switch (op) {
        case 1: {
            inP();
            cout << "\n";
            system("PAUSE");
            break;
        }
        case 2: {
            outP();
            system("PAUSE");
            break;
        }
        case 3: {
            searchP();
            system("PAUSE");
            break;
        }
        case 4: {
            modifyP();
            system("PAUSE");
            break;
        }
        case 5:
        {
            deleteP();
            system("PAUSE");
            break;
        }
        case 6: {
            saveBin();
            break;
        }
        case 7: {
            loadBin();
            break;
        }
        case 8: {
            return 0;
        }
        default: cout << "No ingreso una opcion disponible" << endl;
            break;
        }
    } while (op!=8);

    return 0;
}

void inP() {
    product* nuevo = new product();
    cout << "Ingrese el nombre del producto: ";
    cin >> nuevo->name;

    if (first == NULL) {
        first = nuevo;
        first->next = NULL;
        first->previous = NULL;
        last = first;
    }
    else {
        last->next = nuevo;
        nuevo->next = NULL;
        nuevo->previous = last;
        last = nuevo;
    }

    cout << "Producto agregado correctamente a la lista" << endl;
}

void outP() {
    product* current = new product();
    current = first;

    if (first != NULL) {

        while (current != NULL) {
            cout << "\n" << current->name;
            current = current->next;
        }
    }
    else {
        cout << "No hay productos en la lista" << endl;
        cout << "\n";
    }
    cout << "\n" << endl;
}

void searchP() {

    product* current = new product();
    current = first;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a buscar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                found = true;
            }
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void modifyP() {

    product* current = new product();
    current = first;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a modificar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                cout << "\n Ingrese el nuevo nombre del Producto: ";
                cin >> current->name;
                cout << "\n Producto Modificado Correctamente \n" << endl;
                found = true;
            }
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void deleteP() {

    product* current = new product();
    current = first;
    product* prev = new product();
    prev = NULL;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a eliminar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;

                if (current == first) {
                    if (first->next == NULL) {
                        first = NULL;
                    }
                    else {
                        first = first->next;
                        first->previous = NULL;
                    }
                }
                else if (current == last) {
                    prev->next = NULL;
                    last = prev;
                }
                else {
                    prev->next = current->next;
                    current->next->previous = prev;
                
                }

                cout << "\n Producto Eliminado" << endl;
                found = true;
            }
            prev = current;
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void saveBin() {

    ofstream os(registryName, ios::out | ios::binary);

    if (os.is_open()) {
        product* indice = first;
        while (indice != NULL) {
            os.write((char*)indice, sizeof(product));
            indice = indice->next;
        }
        os.close();
    }

}

void loadBin() {
    ifstream is(registryName, ios::in | ios::binary);
    product* reader;
    
    if (is.is_open()) {
        is.seekg(0, ios::end);
        int size = is.tellg();
        is.seekg(0, ios::beg);

        while (is.tellg() < size) {
            reader = new product;
            is.read((char*)reader, sizeof(product));
            reader->next = NULL;
            cout << reader->name << endl;
            
            if (first == NULL) {
                first = reader;
            }
            else {
                product* indice = first;
                while (indice->next != NULL) {
                    indice = indice->next;
                }
                indice->next = reader;
            }
        }
        is.close();
    }
}

Answer 1

很多很多问题和误解。 。 。

首先。我在代码中的任何地方都看不到链接列表。没有任何地方有带有列表的语句或变量。

相反，您有一个名为“product”的 Node 和 2 个指向该数据类型的全局指针。然后，您手动将 Node 实例链接在一起并相应地更新全局指针。

没有“职责分离”，而且有很多重复。

正常的方法是创建一个 class 或 struct DoublyLinkedList，其中包含节点以及第一个和最后一个指针。然后这个class或struct将提供您需要的所有接口函数，并从oudsite世界隐藏所有内部实现。

然后，进行存储和保存。当然，您永远不会存储节点“products”的指针，也不能将 std::string 存储为二进制文件。 std::string是一种复杂的数据类型，具有一些对您不可见的内部状态。这是行不通的。

相反，您需要对数据进行序列化/反序列化。这意味着您只需将重要数据存储为可读文本即可。

标准方法是覆盖自定义数据类型（此处为“产品”）的插入运算符 << 和提取运算符 >>。

这可以通过简单地添加这些语句（放入您的 struct 定义中）来完成

friend std::ostream& operator << (std::ostream& os, const product& p) { return os << p.name << '\n'; }
friend std::istream& operator >> (std::istream& is, product& p) { return std::getline(is, p.name); }

，这些语句将覆盖 << 和 >> 运算符为您的结构。在函数中，我们只需将“名称”写入流或从流中读取“名称”即可。

定义这些覆盖后，我们可以编写：

product p;
std::cin >> p;
std::cout << p;

编译器将识别与 >> 或 << 运算符一起使用的数据类型“product”并调用函数在您的struct中定义。

---

另外：您对 new 和指针有一些误解。即使不需要，您也总是会创建新的产品。

例如，在“deleteP”函数中，您编写“

    product* current = new product();
    current = first;
    product* prev = new product();
    prev = NULL;

为什么要创建新的“产品”？你只需要定义一个指针。

因此，必须改用以下方法：

    product* current = first;
    product* prev = NULL;

---

这将导致我们遇到代码中的下一个也是最严重的问题。您没有释放使用函数new分配的内存。 new 将通过操作系统/标准库分配/获取内存。并且您分配的所有内存都必须稍后使用 delete 函数再次释放。

由于您没有删除任何内容，因此您正在造成内存泄漏。

所有新建的内容都必须删除。

基本上，C++ 中不应该使用自有内存的 new、delete 和原始指针。

---

但是，一步接着一步。首先，我们用最少的必要修正来修复代码（仍然存在内存泄漏）。但添加反/序列化。

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

string registryName = "products.bin";

struct product {
    string name;
    product* next;
    product* previous;
    friend std::ostream& operator << (std::ostream& os, const product& p) { return os << p.name << '\n'; }
    friend std::istream& operator >> (std::istream& is, product& p) { return std::getline(is, p.name); }
}*first, * last;

void inP();
void outP();
void searchP();
void modifyP();
void deleteP();
void saveBin();
void loadBin();

int main() {


    int op;
    do {
        system("CLS");
        cout << "Menu:" << endl;
        cout << "1. Input a Product " << endl;
        cout << "2. Show the list " << endl;
        cout << "3. Search a Product " << endl;
        cout << "4. Modify a product " << endl;
        cout << "5. Delete a product " << endl;
        cout << "6. Save List " << endl;
        cout << "7. Load Binary List " << endl;
        cout << "8. Exit" << endl;
        cin >> op;
        cout << "\n";

        switch (op) {
        case 1: {
            inP();
            cout << "\n";
            system("PAUSE");
            break;
        }
        case 2: {
            outP();
            system("PAUSE");
            break;
        }
        case 3: {
            searchP();
            system("PAUSE");
            break;
        }
        case 4: {
            modifyP();
            system("PAUSE");
            break;
        }
        case 5:
        {
            deleteP();
            system("PAUSE");
            break;
        }
        case 6: {
            saveBin();
            break;
        }
        case 7: {
            loadBin();
            break;
        }
        case 8: {
            return 0;
        }
        default: cout << "No ingreso una opcion disponible" << endl;
            break;
        }
    } while (op != 8);

    return 0;
}

void inP() {
    product* nuevo = new product();
    cout << "Ingrese el nombre del producto: ";
    cin >> nuevo->name;

    if (first == NULL) {
        first = nuevo;
        first->next = NULL;
        first->previous = NULL;
        last = first;
    }
    else {
        last->next = nuevo;
        nuevo->next = NULL;
        nuevo->previous = last;
        last = nuevo;
    }

    cout << "Producto agregado correctamente a la lista" << endl;
}

void outP() {
    product* current = new product();
    current = first;

    if (first != NULL) {

        while (current != NULL) {
            cout << "\n" << current->name;
            current = current->next;
        }
    }
    else {
        cout << "No hay productos en la lista" << endl;
        cout << "\n";
    }
    cout << "\n" << endl;
}

void searchP() {

    product* current = first;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a buscar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                found = true;
            }
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void modifyP() {

    product* current = first;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a modificar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                cout << "\n Ingrese el nuevo nombre del Producto: ";
                cin >> current->name;
                cout << "\n Producto Modificado Correctamente \n" << endl;
                found = true;
            }
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void deleteP() {

    product* current = first;
    product* prev = NULL;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a eliminar: ";
    cin >> searchP;

    if (first != NULL) {

        while (current != NULL && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;

                if (current == first) {
                    first = current->next;
                    first->previous = NULL;
                }
                else if (current == last) {
                    prev->next = NULL;
                    last = prev;
                }
                else {
                    prev->next = current->next;
                    current->next->previous = prev;
                }
                cout << "\n Producto Eliminado" << endl;
                found = true;
            }
            prev = current;
            current = current->next;
        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void saveBin() {

    ofstream os(registryName);
    if (os) {
        product* indice = first;
        while (indice != NULL) {
            os << *indice;
            indice = indice->next;
        }
    }
}

void loadBin() {
    ifstream is(registryName );
    if (is) {
        std::string name;
        while (is >> name) {
            product *reader = new product;
            reader->name = name;
            reader->next = NULL;
            cout << reader->name << endl;

            if (first == NULL) {
                first = reader;
                first->next = NULL;
                first->previous = NULL;
                last = first;
            }
            else {
                last->next = reader;
                reader->next = NULL;
                reader->previous = last;
                last = reader;
            }
        }
    }
}

这段代码仍然存在很多问题。最大的问题是内存泄漏。而且，还有一个。您没有“clearP”功能，该功能将删除所有节点。这样的“clearP”函数通常必须在任何“loadBin”函数之前调用。否则，如果已经有可用元素，“loadBin”将从磁盘中附加数据到节点末尾。

所以，我们需要添加一个“clearP”函数。在下一步重构中，我们还将释放分配的内存。我们将在“deleteP”函数中执行此操作，并在 main 末尾和“loadBin”函数中调用“clearP”。

通过此更正，我们将得到：

#include <iostream>
#include <fstream>
#include <string>
#include <limits>

using namespace std;

string registryName = "products.bin";

struct product {
    string name;
    product* next;
    product* previous;
    friend ostream& operator << (ostream& os, const product& p) { return os << p.name << '\n'; }
    friend istream& operator >> (istream& is, product& p) { return getline(is, p.name); }
}*first{ nullptr }, * last{ nullptr };

void inP();
void outP();
void searchP();
void modifyP();
void deleteP();
void saveP();
void loadP();
void clearP();

int main() {

    int op = 0;
    do {
        op = 0;
        while (op == 0) {
            system("CLS");
            cout << "Menu:" << endl;
            cout << "1. Input a Product " << endl;
            cout << "2. Show the list " << endl;
            cout << "3. Search a Product " << endl;
            cout << "4. Modify a product " << endl;
            cout << "5. Delete a product " << endl;
            cout << "6. Save List " << endl;
            cout << "7. Load List " << endl;
            cout << "8. Exit" << endl;
            if (not (cin >> op)) {
                op = 0;
                cin.clear();
                cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // skip bad input)
            }
        }
        cout << "\n";

        switch (op) {
        case 1: {
            inP();
            cout << "\n";
            system("PAUSE");
            break;
        }
        case 2: {
            outP();
            system("PAUSE");
            break;
        }
        case 3: {
            searchP();
            system("PAUSE");
            break;
        }
        case 4: {
            modifyP();
            system("PAUSE");
            break;
        }
        case 5:
        {
            deleteP();
            system("PAUSE");
            break;
        }
        case 6: {
            saveP();
            break;
        }
        case 7: {
            loadP();
            break;
        }
        case 8: {
            return 0;
        }
        default: cout << "No ingreso una opcion disponible" << endl;
            break;
        }
    } while (op != 8);

    clearP();

    return 0;
}

void inP() {
    product* nuevo = new product();
    cout << "Ingrese el nombre del producto: ";
    cin >> nuevo->name;

    if (first == nullptr) {
        first = nuevo;
        first->next = nullptr;
        first->previous = nullptr;
        last = first;
    }
    else {
        last->next = nuevo;
        nuevo->next = nullptr;
        nuevo->previous = last;
        last = nuevo;
    }

    cout << "Producto agregado correctamente a la lista" << endl;
}

void outP() {
    product* current = new product();
    current = first;

    if (first != nullptr) {

        while (current != nullptr) {
            cout << "\n" << current->name;
            current = current->next;
        }
    }
    else {
        cout << "No hay productos en la lista" << endl;
        cout << "\n";
    }
    cout << "\n" << endl;
}

void searchP() {

    product* current = first;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a buscar: ";
    cin >> searchP;

    if (first != nullptr) {

        while (current != nullptr && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                found = true;
            }
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void modifyP() {

    product* current = first;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a modificar: ";
    cin >> searchP;

    if (first != nullptr) {

        while (current != nullptr && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;
                cout << "\n Ingrese el nuevo nombre del Producto: ";
                cin >> current->name;
                cout << "\n Producto Modificado Correctamente \n" << endl;
                found = true;
            }
            current = current->next;

        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void deleteP() {

    product* current = first;
    product* prev = nullptr;
    product* toDelete = nullptr;
    bool found = false;

    string searchP;

    cout << "Ingrese el producto a eliminar: ";
    cin >> searchP;

    if (first != nullptr) {

        while (current != nullptr && found != true) {

            if (current->name == searchP) {
                cout << "\n Producto ( " << searchP << " ) Encontrado \n" << endl;

                if (current == first) {
                    toDelete = first;
                    first = current->next;
                    first->previous = nullptr;
                    delete toDelete;
                }
                else if (current == last) {
                    toDelete = last;
                    prev->next = nullptr;
                    last = prev;
                    delete toDelete;
                }
                else {
                    toDelete = current;
                    prev->next = current->next;
                    current->next->previous = prev;
                    delete toDelete;
                }
                cout << "\n Producto Eliminado" << endl;
                found = true;
            }
            prev = current;
            current = current->next;
        }
        if (!found) {
            cout << "\n Producto no encontrado \n" << endl;
        }
    }
    else {
        cout << "\n La lista de productos esta vacia \n" << endl;
    }
}

void saveP() {

    ofstream os(registryName);
    if (os) {
        product* indice = first;
        while (indice != nullptr) {
            os << *indice;
            indice = indice->next;
        }
    }
}

void loadP() {
    ifstream is(registryName );
    if (is) {
        clearP();
        string name;
        while (is >> name) {
            product *reader = new product;
            reader->name = name;
            reader->next = nullptr;
            cout << reader->name << endl;

            if (first == nullptr) {
                first = reader;
                first->next = nullptr;
                first->previous = nullptr;
                last = first;
            }
            else {
                last->next = reader;
                reader->next = nullptr;
                reader->previous = last;
                last = reader;
            }
        }
    }
}

void clearP() {

    product* current = first;
    product* next = nullptr;

    if (first != nullptr) {

        while (current != nullptr) {
            next = current->next;
            delete current;
            current = next;
        }
    }
    first = nullptr;
    last = nullptr;
}

仍然不是真正的链接列表，但已经可以工作。

不幸的是，我无法向您展示真实列表的一些示例实现，因为 SO 将答案的长度限制为 30000 。 。 。