在C++中，實現命令模式的撤銷功能需要遵循以下步驟：

1. 定義一個命令接口（Command）：

class Command {
public:
    virtual ~Command() {}
    virtual void execute() = 0;
    virtual void undo() = 0;
};

2. 為每個具體命令創建一個類，實現命令接口：

class ConcreteCommandA : public Command {
private:
    Receiver* receiver;

public:
    ConcreteCommandA(Receiver* receiver) : receiver(receiver) {}

    void execute() override {
        receiver->actionA();
    }

    void undo() override {
        receiver->undoActionA();
    }
};

class ConcreteCommandB : public Command {
private:
    Receiver* receiver;

public:
    ConcreteCommandB(Receiver* receiver) : receiver(receiver) {}

    void execute() override {
        receiver->actionB();
    }

    void undo() override {
        receiver->undoActionB();
    }
};

3. 創建一個命令管理器（CommandManager），用于存儲和管理命令對象，并提供執行和撤銷功能：

#include <stack>

class CommandManager {
private:
    std::stack<Command*> commandStack;

public:
    void executeCommand(Command* command) {
        command->execute();
        commandStack.push(command);
    }

    void undoLastCommand() {
        if (!commandStack.empty()) {
            Command* command = commandStack.top();
            commandStack.pop();
            command->undo();
        }
    }
};

4. 創建一個接收者（Receiver）類，包含實際要執行的操作和撤銷操作：

class Receiver {
public:
    void actionA() {
        // 實際執行操作A
    }

    void undoActionA() {
        // 撤銷操作A
    }

    void actionB() {
        // 實際執行操作B
    }

    void undoActionB() {
        // 撤銷操作B
    }
};

5. 在客戶端代碼中，使用命令模式執行和撤銷操作：

int main() {
    Receiver receiver;
    CommandManager commandManager;

    Command* commandA = new ConcreteCommandA(&receiver);
    Command* commandB = new ConcreteCommandB(&receiver);

    commandManager.executeCommand(commandA);
    commandManager.executeCommand(commandB);

    commandManager.undoLastCommand();

    delete commandA;
    delete commandB;

    return 0;
}

這樣，我們就實現了一個簡單的命令模式的撤銷功能。當然，實際應用中可能需要根據具體需求對這個實現進行擴展和優化。