如何在 main 之外的函数中创建对象？

Question

一切运行良好，但我的问题是我的主要功能太长了。有没有办法在主功能之外创建战斗场景？我已经尝试过了，但是如果我将战斗场景——让我们说“Battle()”——放在头文件或其他东西中，那么我的对象会产生错误。有什么方法可以使我在 main 函数之外的 main 中声明的对象。也许使用指针或其他东西？

 int main()
    {
        Hero Me(100,20,30,40);//Created using overloaded constructor
        Monster m(100,16,18,20);//creates a monster object and uses overloaded constructor to initialize

    cout << "\nAttacking!\n";

//I want this part to be in a function called Battle() outside of main
    while ((Me.getHp() > 0) && (m.getHp() > 0))//Generates error if object not declared in main
    {   
        cout << "\nYour hp is: " << Me.getHp() << endl;
        cout << "The enemy's hp is: "<< m.getHp() << endl;
        cout << "\nThe monster has attacked you!\n";
        cout << "You received " << m.getAttack() << " damage;" << endl;
        Me.damageTaken(m.getAttack());//Me.setHp(Me.getHp() - m.getAttack());//Me.setHp(m.getStrength());
        if(Me.getHp() > 0)//Check if still alive
        {
            cout << "\nYour hp is now: " << Me.getHp() << endl;
            //cout << "Enemy hp is: "<< m.getHp() << endl;
            cout << "\nNow you attacked!\nYou have dealt "<< Me.getAttack() << " Damage" << endl;
            m.damageTaken(Me.getAttack());//m.setHp(m.getHp() - Me.getAttack());//m.setHp(Me.getAttack());

            if(m.getHp() > 0)//Check if still alive
            {
                cout << "Enemy hp is now: " << m.getHp() << endl;
                cout << "\nAttacking again!\n";
            }
        }

    } 
        if ((Me.getHp() > 0) && (m.getHp() <= 0))
                cout <<"\nCongratulations! You killed the enemy!" << endl;

        else if ((Me.getHp() <= 0) && (m.getHp() > 0))
                cout << "You have died!" << endl;




    cin.sync();
    cin.get();
    return 0;
}

如果代码如下：

//Hero.h
class Hero:
    public Character
{
public:
    Hero();
    Hero(int, int, int, int);
    ~Hero();

};

//Hero.cpp
Hero::Hero(int newHp, int newLevel, int newAttack, int newDef)
    : Character(newHp, newLevel, newAttack, newDef)
{
    cout << "Hero created using Overloaded function!\n";
    hp = newHp;
    cout << "Hp is: "<< hp << endl;
    level = newLevel;
    cout << "level is: " << level << endl;
    attack = newAttack;
    cout << "Attack is: " << attack << endl;
    defense = newDef;
    cout << "Defense is: " << defense << endl;
    // logging goes here
    // note that you don't need HeroLevel etc. at all any more, just use level
}

Hero::~Hero()
{
    cout << "Hero destroyed!\n";
}


//Monster.h
class Monster:
    public Character //Hero
{
public:
    Monster();
    Monster(int, int, int, int); //explicit
        //:Character(){};
    //Monster(int);
    ~Monster();
};

//Monster.cpp
Monster::Monster(int newHp, int newLevel, int newAttack, int newDef)
    //: hp(newHp), level(newLevel), attack(newAttack), defense(newDef)//initialize list
{
    cout << "Monster created using Overloaded function!\n";
    hp = newHp;
    cout << "Hp is: "<< hp << endl;
    level = newLevel;
    cout << "level is: " << level << endl;
    attack = newAttack;
    cout << "Attack is: " << attack << endl;
    defense = newDef;
    cout << "Defense is: " << defense << endl;
}

Monster::~Monster()
{
    cout << "\nMonster Destroyed";
}

//Character.h
class Character
{

protected://not private, so derived class can use it
    int level;
    int hp;
    int attack;
    int defense;
    Character(); // zero everything by default
    Character(int); // randomly generate everything
    Character(int, int, int, int); // populate explicitly
    ~Character();
public:
    int getAttack() const { return attack; }
    int getDefense() const { return defense; }
    int getHp() const { return hp; }
    int getlevel() const { return level; }

    void setAttack(int);
    void setDefense(int);
    void setStrength(int);
    void setHp(int);
    void setlevel(int);
    void damageTaken(int);

//Character.cpp
Character::Character() : level(0), hp(0), attack(0), defense(0) {}

Character::Character(int hit, int lvl, int att, int def)
 : level(lvl), hp(hit), attack(att), defense(def){}


Character::~Character()
{
    cout << "Character has been destroyed!\n";
}

Answer 1

你可以通过三种方式做到这一点：

1. 返回副本。这可能是首选方式，对于简单对象来说也是最简单的方式。

   此类函数的示例：

   Hero create_hero()
   {
       Hero hero{...};
   
       // Other stuff
   
       return hero;
   }
   

2. 返回引用。这里最大的警告是您不能返回对局部变量的引用，您必须返回对存储在其他地方（例如向量中）的数据的引用。

3. 返回指针。这与数字 2 有相同的警告，返回一个指向局部变量的指针，例如return &some_local_var; 是个坏主意。

   此类函数的示例：

   std::unique_ptr<Hero> create_hero()
   {
       auto hero = std::unique_ptr<Hero>(new Hero{...});
   
       // other stuff
   
       // remember that `hero` is a pointer, so the `->` operator has to be used
       // when dereferencing the variable
       // e.g. `hero->some_function()`
   
       return hero;
   }
   

对于第 1 点，如果您有任何类型的复杂对象，您应该了解the rule of three。

对于第 3 点，我建议使用智能指针，例如 std::unique_ptr 或 std::shared_ptr，如我的示例所示。