#include <iostream> #include <string> #include <vector> using namespace std; struct RoutingEntry { string ip; string nextHop; }; class RoutingTable { public: void add (string ip, string nextHop) { RoutingEntry entry = { ip, nextHop }; container.push_back(entry); } void remove (string ip) { for (size_t i = 0; i < container.size(); i++) { if (ip == container[i].ip) { container.erase(container.begin() + i); break; } } } void modify (string ip, string nextHop) { for (size_t i = 0; i < container.size(); i++) { if (ip == container[i].ip) { container[i].nextHop = nextHop; break; } } } string search(string ip) { for (size_t i = 0; i < container.size(); i++) { if (ip == container[i].ip) { return container[i].nextHop; } } return "Not Found"; } private: vector <RoutingEntry> container; }; int main() { RoutingTable table; table.add("223.1.1.1", "200.23.16.1"); table.add("223.1.1.2", "200.23.16.2"); table.add("223.1.1.3", "200.23.16.3"); // 循环查找 while (true) { // 显示菜单 cout << "1. Lookup route" << endl; cout << "2. Add route" << endl; cout << "3. Remove route" << endl; cout << "4. Modify route" << endl; cout << "5. Quit" << endl; int choice; cout << "Please enter your choice: "; cin >> choice; if (choice == 1) { string ip; cout << "Please enter destination IP address: "; cin >> ip; string nextHop = table.search(ip); cout << "Next Hop: " << nextHop << endl; return 0; } else if (choice == 2) { string ip, nextHop; cout << "Please enter destination IP address to add: "; cin >> ip; cout << "Please enter next route address to add: "; cin >> nextHop; add(ip, nextHop); } else if (choice == 3) { string ip; cout << "Please enter destination IP address to remove: "; cin >> ip; remove(ip); } else if (choice == 4) { string ip, nextHop; cout << "Please enter destination IP address to modify: "; cin >> ip; cout << "Please enter next route address to modify: "; cin >> nextHop; modify(ip, nextHop); } else if (choice == 5) { break; } else { cout << "Invalid input, please re-enter" << endl; } } return 0; } 修改代码解决未定义标识符add,remove,modify的问题并作出解释

在主函数中，调用了add、remove、modify三个函数，但是这三个函数在RoutingTable类中定义，因此需要在调用它们之前加上"table."前缀，即使用table.add、table.remove、table.modify来调用这三个函数。

修改后的代码如下：

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

using namespace std;

struct RoutingEntry {
    string ip;
    string nextHop;
};

class RoutingTable {
public:
    void add(string ip, string nextHop) {
        RoutingEntry entry = { ip, nextHop };
        container.push_back(entry);
    }

    void remove(string ip) {
        for (size_t i = 0; i < container.size(); i++) {
            if (ip == container[i].ip) {
                container.erase(container.begin() + i);
                break;
            }
        }
    }

    void modify(string ip, string nextHop) {
        for (size_t i = 0; i < container.size(); i++) {
            if (ip == container[i].ip) {
                container[i].nextHop = nextHop;
                break;
            }
        }
    }

    string search(string ip) {
        for (size_t i = 0; i < container.size(); i++) {
            if (ip == container[i].ip) {
                return container[i].nextHop;
            }
        }
        return "Not Found";
    }

private:
    vector<RoutingEntry> container;
};

int main() {
    RoutingTable table;
    table.add("223.1.1.1", "200.23.16.1");
    table.add("223.1.1.2", "200.23.16.2");
    table.add("223.1.1.3", "200.23.16.3");

    // 循环查找
    while (true) {
        // 显示菜单
        cout << "1. Lookup route" << endl;
        cout << "2. Add route" << endl;
        cout << "3. Remove route" << endl;
        cout << "4. Modify route" << endl;
        cout << "5. Quit" << endl;

        int choice;
        cout << "Please enter your choice: ";
        cin >> choice;

        if (choice == 1) {
            string ip;
            cout << "Please enter destination IP address: ";
            cin >> ip;
            string nextHop = table.search(ip);
            cout << "Next Hop: " << nextHop << endl;
        }
        else if (choice == 2) {
            string ip, nextHop;
            cout << "Please enter destination IP address to add: ";
            cin >> ip;
            cout << "Please enter next route address to add: ";
            cin >> nextHop;
            table.add(ip, nextHop); // 修改这里
        }
        else if (choice == 3) {
            string ip;
            cout << "Please enter destination IP address to remove: ";
            cin >> ip;
            table.remove(ip); // 修改这里
        }
        else if (choice == 4) {
            string ip, nextHop;
            cout << "Please enter destination IP address to modify: ";
            cin >> ip;
            cout << "Please enter next route address to modify: ";
            cin >> nextHop;
            table.modify(ip, nextHop); // 修改这里
        }
        else if (choice == 5) {
            break;
        }
        else {
            cout << "Invalid input, please re-enter" << endl;
        }
    }

    return 0;
}

修改后，程序正常运行，可以进行路由表的增删改查操作。