无法访问静态函数内的私有变量

Question

I'm trying to make a small mini game where a class Hero interacts with class Enemy variables using friend but the code is unable to compile and gives me the forward declaration error

#include <iostream>

class Enemy;

class Hero
{
    friend class Enemy;
private:
    static int hp, power;
public:
    Hero *h1;
    Hero ()
    {
        hp = 50;
        power = 10; 
    }
    static void attackEnemy (Enemy *e1, Hero *h1);
};

static void Hero::attackEnemy(Enemy *e1, Hero *h1)
{
    e1->hp -= h1->power;
}

class Enemy
{
    friend class Hero;
private:
    static int hp, power;
public:
    Enemy ()
    {
        hp = 15;
        power = 10;
    }
    void attackHero ();
};

int main ()
{
    Enemy *e1 = new Enemy ();
    Hero *h1 = new Hero ();

    h1->attackEnemy(Enemy *e1, Hero *h1);

    return 0;
}

I was told that static functions and variables are able to prevent this error as they are global as it pre-compiles the build

Answer 1

There are two main issues here.

First, when defining Hero::attackEnemy , the static qualifier is invalid here. The member is already declared as static in the class definition, so no need to apply it here as well.

Second, at the time Hero::attachEnemy is defined, the Enemy class still has not been defined. You need to move the definition of Hero::attachEnemy after the definition of class Enemy .

class Enemy;

class Hero {
    ...
};

class Enemy {
    ...
};

void Hero::attackEnemy(Enemy *e1, Hero *h1)
{
    e1->hp -= h1->power;
}

Also, this is not a valid function / method call:

h1->attackEnemy(Enemy *e1, Hero *h1);

You want:

h1->attackEnemy(e1, h1);