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ChainedHollow

Passing an object to constructor of another object? C++

8 posts in this topic

Hi everyone! I am hoping someone can help me out with this. I've been looking around online all night and I am so confused.
 
I have 2 classes, and 1 sub-class. Spell, Heal::Spell, and Hero;
 
Spell is a friend class of Hero and Heal is a subclass of Spell.
I need Heal to be able to make changes to a Hero object, so I am wanting to pass a pointer to the Hero object to the Heal constructor. 
 
If someone can help me with this I would be so grateful! I will include my code, so far.
 
classes.h
Spell
{
public:
     // code
private:
     Hero &hero;
}
 
Heal(const Hero& h)
{
public:
     // code
protected:
     // code
}
 
classes.cpp
Heal::Heal(const Hero& h): hero(h)
{
     //code
}
Thats basically what I have for the classes. Any clarification on how to fix this???
 
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I am so thoroughly confused by the syntax you are using. Did you by any chance mean something more like this? 

class Hero
{
	// Awesome and clean code
};

class Spell
{
public:
	// Awesome and clean interface
private:
	friend class Hero; // Ouch, not too awesome

	Hero &hero;
};

class Heal : public Spell
{
public:
	Heal(const Hero&);
	
protected:
	// Helper functions
};

Well, in order to pass a modifiable Hero pointer to Heal, you need to watch out for a couple of things.

 

One, you are passing a const Hero, which means you won't be able to modify it. Remove the const keyword if you want to modify the object.

 

Two, as far as I can tell, you're passing Hero to the wrong object. The member variable hero in Spell is declared private and trying to assign a value to it from Heal will generate a compiler error. 

 

Try fixing those errors and see if you can get it to do what you want.

Edited by boogyman19946
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You can pass it into Heal's constructor, and Heal can pass it to Spell's constructor:
 
class Spell
{
public:
     Spell(const Hero& h) : hero(h) { }

protected:
     Hero &hero;
};
 
class Heal
{
public:
     Heal(const Hero& h) : Spell(h) { }

};
Though, really, you probably shouldn't pass in Hero until the spell is ready to be used:
class Spell
{
public:
     Spell() { }

     virtual void UseOn(Hero &hero) = 0;
};
 
class Heal
{
public:
     Heal() { }

     void UseOn(Hero &hero) override
     {
        float amountToHeal = float(hero.maxHealth) * 0.25f;
        hero.health = (int)amountToHeal;
     }
};
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I see, thank you. It seems I have fixed the errors with the classes, but I don't if it's working yet because calling it is giving me an error now.

I removed const, as was mentioned, and I moved Hero& hero to the protected section of Heal. Then I have:

 

 

spells.push_back(new Heal(heroes.at(0)) );

 

spells is a vector made above. std::vector<Spell*> spells;

and heroes is the hero vector. std::vector<Hero*> heroes;

 

This just isn't working now. Am I calling it wrong?

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error C2664: 'Heal::Heal(Hero &)' : cannot convert parameter 1 from 'Hero **' to 'Hero &'

 

I've tried adding & and * but that doesn't work either.

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'Hero **' means it's a pointer to a pointer to a Hero. '*expression' will turn it into a pointer to a Hero. '**expression' will turn it into a Hero which the compiler can convert into a reference to a Hero as desired.

However, a double pointer feels like you have gone too far down the rabbit hole. You should seriously consider taking several steps backwards and doing more exercises regarding types.
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You're passing in a pointer but the Constructor Is expecting a reference. Make the call

spells.push_back(new Heal(*heroes.at(0)));

You have to dereference the pointer.
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