'View v' 类型不完整，无法定义 C++

Question

#include <iostream>
#include <string>
#include <vector>

class Contact;
class Controller;
class View;

class Contact {
private:
    std::string name;
    std::string phone;
public:
    std::string get_name() {
        return name;
    }
    std::string get_phone() {
        return phone;
    }
    void set_name(std::string name) {
        this->name = name;
    }
    void set_phone(std::string phone) {
        this->phone = phone;
    }
};

class Controller {
public:
    void delete_contact(std::vector<Contact> &data) {
        std::cout << "Choose a number from 1 to 3.\n";
        std::cout << "1. Delete by id\n";
        std::cout << "2. Delete by name\n";
        std::cout << "3. Delte by phone\n";
        int choice;
        std::cin >> choice;
        enum { ID = 1, NAME = 2, PHONE = 3 };
        if (choice == ID) {
            int id;
            std::cout << "Enter id: \n";
            std::cin >> id;
            delete_by_id(data, id);
        }
        else if (choice == NAME) {
            std::string name;
            std::cout << "Enter name: \n";
            std::cin >> name;
            delete_by_name(data, name);
        }
        else if (choice == PHONE) {
            std::string phone;
            std::cout << "Enter phone: \n";
            std::cin >> phone;
            delete_by_phone(data, phone);
        }
        else {
            std::cerr << "Wrong choice.\n";
        }

    }
    void delete_by_id(std::vector<Contact> &data, const int id) {
        // valid ids are in range [1 .. data.size()]
        if (id < data.size() || id > data.size()) {
            std::cerr << "id not found\n";
            return;
        }
        std::cout << "Contact " << id << " deleted successfully\n";
    }
    void delete_by_name(std::vector<Contact> &data, const std::string name) {
        int id = -1;
        // assuming unique names
        for (int i = 0; i < data.size(); i++) {
            if (data[i].get_name() == name) {
                id = i;
                break;
            }
        }
        if (id == -1) {
            std::cerr << "Contact with " << name << " is not found\n";
            return;
        }
        data.erase(data.begin() + id);
    }
    void delete_by_phone(std::vector<Contact> &data, const std::string phone) {
        int id = -1;
        for (int i = 0; i < data.size(); i++) {
            if (data[i].get_name() == phone) {
                id = i;
                break;
            }
        }
        if (id == -1) {
            std::cerr << "Contact with " << phone << " is not found\n";
            return;
        }
        data.erase(data.begin() + id);
    }
    void add_contact(Contact new_contact, std::vector<Contact> &data) {
        data.push_back(new_contact);
    }
    void search_contact(std::vector<Contact> &data) {
        std::cout << "1. Search by id.\n";
        std::cout << "2. Search by name.\n";
        std::cout << "3. Search by phone.\n";
        enum { ID = 1, NAME = 2, PHONE = 3 };
        int choice;
        std::cin >> choice;
        if (choice == ID) {
            int id;
            std::cout << "Enter id: \n";
            std::cin >> id;
            search_by_id(data, id);
        }
        else if (choice == NAME) {
            std::string name;
            std::cout << "Enter name: \n";
            std::cin >> name;
            search_by_name(data, name);
        }
        else if (choice == PHONE) {
            std::string phone;
            std::cout << "Enter phone: \n";
            std::cin >> phone;
            search_by_phone(data, phone);
        }
        else {
            std::cerr << "Wrong choice.\n";
        }


    }
    void search_by_id(std::vector<Contact> &data, int id) {
        if (id < data.size() || id > data.size()) {
            std::cerr << "Contact not found\n";
            return;
        }
        View v;
        v.print_contact_data(data[id]);

    }
    void search_by_name(std::vector<Contact> &data, const std::string name) {
        int id = -1;
        for (int i = 0; i < data.size(); i++) {
            if (data[i].get_name() == name) {
                id = i;
                break;
            }
        }
        if (id == -1) {
            std::cerr << "Contact not found\n";
            return;
        }
        View v;
        v.print_contact_data(data[id]);
    }
    void search_by_phone(std::vector<Contact> &data, const std::string phone) {
        int id = -1;
        for (int i = 0; i < data.size(); i++) {
            if (data[i].get_phone() == phone) {
                id = i;
                break;
            }
        }
        if (id == -1) {
            std::cerr << "Contact not found\n";
            return;
        }
        View v;
        v.print_contact_data(data[id]);
    }
    void edit_contact(std::vector<Contact> &data) {
        std::cout << "Enter contact id\n";
        int id;
        std::cin >> id;
        if (id < data.size() || id > data.size()) {
            std::cerr << "Sorry, wrong id\n";
        }
        std::cout << "Do you want to edit this contact? [Y, N]\n";
        View v;
        v.print_contact_data(data[id]);
        std::string choice;
        std::cin >> choice;
        if (choice.front() == 'Y') {
            std::cout << "Enter new name:\n";
            std::string name;
            std::cin >> name;
            data[id].set_name(name);
            std::cout << "Enter new phone:\n";
            std::string phone;
            std::cin >> phone;
            data[id].set_phone(phone);
            std::cout << "Done\n";

        }
        else {
            std::cerr << "Wrong choice.\n";
        }

    }
};

class View {
public:
    
    std::vector<Contact> data;
    void print_contact_data(Contact data) {
        std::cout << data.get_name() << ' ' << data.get_phone() << '\n';
    }
    void print_all_contacts() {
        int curr = 1;
        for (auto x : data)
            std::cout << curr++ << ". " << x.get_name() 
            << ' ' << x.get_phone() << '\n';

    }
    Contact get_contact_data() {
        Contact data;
        std::cout << "Enter contact name:\n";
        std::string name;
        std::cin >> name;
        std::cout << "Enter contact phone:\n";
        std::string phone;
        std::cin >> phone;
        data.set_name(name);
        data.set_phone(phone);
        return data;

    }
    void main_menu() {
        enum { ADD = 1, DELETE = 2, EDIT = 3,
            SEARCH = 4, PRINT = 5, EXIT = 6 };
        std::cout << "1. Add contact\n";
        std::cout << "2. Delete contact\n";
        std::cout << "3. Edit contact\n";
        std::cout << "4. Search contact\n";
        std::cout << "5. Print all contacts\n";
        std::cout << "6. Exit\n";
        int choice;
        std::cin >> choice;
        Controller temp;
        if (choice == ADD) {

            temp.add_contact(get_contact_data(), data);

        } else if (choice == DELETE) {
            temp.delete_contact(data);
            
        } else if (choice == EDIT) {
            temp.edit_contact(data);
        } else if (choice == SEARCH) {
            temp.search_contact(data);
        } else if (choice == PRINT) {
            print_all_contacts();
        } else if (choice == EXIT) {
            exit(0);
        } else {
            std::cout << "Wrong choice\n";
        }

    }
};



int main() {
    View v;
    v.main_menu();
    return 0;
}

我试图实现 MVC 设计模式。 基本上，这是一个基本的联系人管理系统。 可以添加、删除、编辑、搜索联系人。 View 类负责用户操作并与用户交互。 接触类只是模型。 我收到此错误消息“'View v' 的类型不完整，无法定义”。 我搜索了一些解决方案，但找不到我的错误是什么。

Answer 1

您具有以下代码结构：

class Contact;
class Controller;
class View;

class Controller {
public:
    // ...
    void search_by_id(std::vector<Contact> &data, int id) {
        // ...
        View v;
        // ...
    }
    // ...
};

class View {
public:
    // ...    
    void main_menu() {
        // ...
        Controller temp;
        // ...
    }
    // ...
};

这会产生错误，因为View v; 需要定义View 。 将View的定义移到Controller之前不会解决问题，因为Controller temp; 会有同样的问题。

简单的解决方法是将所有函数定义移到类之外，并在定义其他类之后：

class Controller {
public:
    // ...
    void search_by_id(std::vector<Contact> &data, int id);
    // ... 
};

class View {
public:
    // ...
    void main_menu();
    // ...
};

void View::main_menu() {
    // ...
    Controller temp;
    // ...
}

void Controller::search_by_id(std::vector<Contact> &data, int id) {
    // ...
    View v;
    // ...
}