I''m practising my skills in the field of OO and made a simple MOnster class. The I derived a Grunt class from it, but my compiler doesn''t seem too happy about this stuff:

  
#include <iostream.h>
#include <string.h>

//The main monster class

class CMonster
{
	int strength;
	int weapon;
	int armor;
public:
	CMonster();
	CMonster(int, int, int);
	virtual ~CMonster();
	virtual void Attack();
	virtual void Move();
};
CMonster::CMonster(int p_str, int p_wpn, int p_armor)
{
	strength = p_str;
	weapon = p_wpn;
	armor = p_armor;
}
void CMonster::Attack()
{
	cout<<"Monster attacks!\n";
}
void CMonster::Move()
{
	cout<<"Monster moves!\n";
}

//Derived class

class CGrunt : public CMonster
{
	char name[10];
public:
	CGrunt();
	CGrunt(int, int, int, const char *);
	~CGrunt();
	void Attack();
	void Move();
};
CGrunt::CGrunt(int p_str, int p_wpn, int p_armor, const char *p_name) : CMonster(p_str, p_wpn, p_armor)
{	
	strcpy(name, p_name);
}
void CGrunt::Attack()
{
	cout<<name<<" attacks!\n";
}
void CGrunt::Move()
{
	cout<<name<<" moves!\n";
}

int main()
{
	CMonster *monster = new CMonster(1,2,3);
	CMonster *xjussix = new CGrunt(1,2,3, "xjussix");
	xjussix->Move();
	xjussix->Attack();
	monster->Attack();
	monster->Move();
	delete monster;
	delete xjussix;
	return 0;
}
  

error LNK2001: unresolved external symbol "public: virtual __thiscall CMonster::~CMonster(void)" (??1CMonster@@UAE@XZ) error LNK2001: unresolved external symbol "public: virtual __thiscall CGrunt::~CGrunt(void)" (??1CGrunt@@UAE@XZ) Debug/TYCPP21.exe : fatal error LNK1120: 2 unresolved externals My first completed game! Where''s that???

THANK YOU! Stupid ''ol me strikes again
I knew there was stupid mistake and there was. BTW, do I always have to implement destructors, or do I have to do that only when I have virtual functions in a class?

My first completed game! Where''s that???

another possible refinement here...

because it''s a constructor it''s likely to always be used because a constructor is automatically called when you define an object of a given class.

maybe the compiler is forcing you to implement the constructor because it knows it will be called.

WeP
http://www.planetzztpp.com

quote:Untrue, unfortunately. It''s perfectly legal to declare away to your heart''s content: free functions, member functions, external variables, anything. Your code will still compile--unless you use those names.

True, but constructors and destructors are never called explicitly by name. That is, you can''t code classInstance.className() to call a constructor or classInstance.~className() to call a destructor. I think that gmcbay meant that if you declare a constructor, you must implement it if any objects are created using that constructor and if you declare the destructor for a class you must also implement that if any objects of the class are created (and therefore eventually destroyed). You can get away with declaring and not implementing constructors only if no objects are created with that constructor.

-Sean

That''ll teach me to jump in without having all the facts. Up until today I was pretty secure in my knowledge of constructors and destructors.

Allow me to jump into defensive mode for a minute :
What I was trying to do was point out that although most functions can be declared and not implemented as long as no explicit function call is made to them, constructors and destructors are a special case because (most of the time at least, as I have just learned) you don''t see the function call in the code. You could say an object declaration or dynamic allocation is the call to the constructor and I won''t argue, but in the case of the default constructor, it looks even less like a regular function call. And to be honest, I didn''t look closely at the original poster''s code and thought part of his problem was with declaring but not implementing the default constructor (which is true but I see now he didn''t create any objects with the default). But it''s certainly rare to see an explicit call to the destructor (or am I just not looking at enough code from other programmers?)

Anybody ever use "ptr->~ty();" or know how it differs from "delete ptr;"? Is it just a case of two ways of doing the same thing?

-Sean