C++ 从链表中删除

Question

所以在我当前的程序中，我的任务是存储一个分支向量。这些分支包含一个字符串名称和一个指向节点的指针。

这些节点存储一本书，其中包含作者姓名、标题和副本数。

总的来说，这应该创建一个链表的数据结构。

目前我正在尝试编写一个程序来从分支中删除或“签出”某本书。

将这些书添加到分支AO之后。

斯坦·穆恩

比尔·孙

克里斯地面

兰天空

我尝试查看 Chris 的书 Ground。如果这本书有多个副本（在这种情况下它没有），它只会将副本数量减少一份。如果它只有一个副本，则删除它，将先前指向它的对象设置为 Ground 指向的对象，然后删除 Ground 与其下一个之间的链接。

但是，由于某种原因，在执行此功能后，我的链表没有任何变化。这是有原因的吗？

提前致谢！

#include "Library.h"
#include <vector>
#include <string>
#include <iostream>

using namespace std;
int total;
int index;

Library::Library()
{

}

struct Node //Has everything in it
{
    string author;
    string title;
    int copies;
    Node* next;
};

struct Branch // Stores just the branch, and a point to the node with information in it.
{
    string b_name;
    Node* next;
};

vector<Branch*> lib;

void Library::start()
{
    int choice = 0;
    do
    {
        cout << "Please select a choice." << endl;
        cout << " " << endl;
        cout << "1. Create a branch and insert its books" << endl;
        cout << "2. Given an author name, a title and a branch name, CHECKOUT that book from the branch." << endl;
        cout << "3. Given an author name, title and a branch name, RETURN that book to the branch." << endl;
        cout << "4. Given an author name, title and branch name, FIND the number of copies of that book are available in that branch." << endl;
        cout << "5. PRINT all books contained in a branch." << endl;
        cout << "6. Exit the program." << endl;

        cin >> choice;

        switch (choice)
        {
        case 1:
            insert();
            break;

        case 2:
            checkout();
            break;

        case 3:
            Return();
            break;

        case 4:
            find();
            break;

        case 5:
            printAll();
            break;

            // TODO: other choises
        }
    } while (choice != 6);
}

void Library::insert()
{
    string br;
    string auth;
    string titl;

    cout << "What is the name of the branch?" << endl;
    cin >> br;

    Branch *branch = new Branch();
    branch->b_name = br;
    lib.push_back(branch);
    Node* lastNode = nullptr;

    do
    {
        cout << "What is the author and title of the book?" << endl;
        cin >> auth >> titl;
        if (auth == "NONE" && titl == "NONE") break;

        Node *book = new Node();
        book->author = auth;
        book->title = titl;
        book->copies++;
        if (lastNode == nullptr) {
            branch->next = book;
        }
        else {
            lastNode->next = book;
        }
        lastNode = book;
    } while (auth != "NONE" && titl != "NONE");

    start();
}

void Library::checkout()
{
    string auth;
    string titl;
    string bran;
    bool success = false;

    cout << "Insert author, title and branch" << endl;
    cin >> auth >> titl >> bran;

    for (unsigned int i = 0; i < lib.size(); i++)
    {
            auto* branch = lib[i];
            auto* node = branch->next;
            Node* previous = nullptr;

            while (node)
            {
                if (node->author == auth && node->title == titl && branch->b_name == bran)
                    if (node->copies > 1) node->copies--; success = true;  break;
                if (node->copies == 1)
                {
                    previous->next = node->next;
                    node->next = nullptr;
                    success = true;
                    break;
                }

                if (!success)
                {
                    previous = node;
                    node = node->next;
                }

            }
            if (success)
            {
                cout << "Complete!" << endl;
                cout << "" << endl;
            }


    }
    start();
}

Answer 1

这个呢：

    void Library::checkout()
{
    string auth;
    string titl;
    string bran;
    bool success = false;

    cout << "Insert author, title and branch" << endl;
    cin >> auth >> titl >> bran;

    for (unsigned int i = 0; i < lib.size(); i++)
    {
        auto* branch = lib[i];
        auto* node = branch->next;
        Node* previous = nullptr;

        while (node)
        {
            if (node->author == auth && node->title == titl && branch->b_name == bran)
            {
                if (node->copies > 1)
                {
                    node->copies--;
                    success = true; 
                    break;
                }
                else
                {
                    if (previous)
                    {
                        previous->next = node->next;
                    }
                    else
                    {
                        branch->next = node->next;
                    }
                    delete node;
                    success = true;
                    break;
                }
            }
            previous = node;
            node = node->next;
        }
        if (success)
        {
            cout << "Complete!" << endl;
            cout << "" << endl;
        }
    }
    //  no need to call start() as start() has a do/while loop
    // start();

}

编辑：修复删除条件的错误放置