Inheritance :Getting back to the basics

**csonx_p** · 03-16-2009

Hi, please help

Code:

#include <iostream> 

class Base {

public:
	Base ( int d ) {data = d;}
	void Show() { std::cout << "I'm showig off " << data << " in base"; }
private :
	int data;
};

class Derived : public Base {

public:
	Derived() {}
	void Showd() {
		Show();
	}
};

void main () {
	Base b(5);
	Derived	d;
	d.Show();
}

: error C2512: 'Base' : no appropriate default constructor available ?????

**laserlight** · 03-16-2009

Yes, since Base has a user declared constructor, the compiler will not provide it a default constructor. Now, the Derived class default constructor implicitly invokes Base's default constructor, hence the error. You can either explicitly initialise Base in the Derived default constructor's initialisation list, or you can provide Base with a default constructor.

**csonx_p** · 03-16-2009

Originally Posted by laserlight

Yes, since Base has a user declared constructor, the compiler will not provide it a default constructor. Now, the Derived class default constructor implicitly invokes Base's default constructor, hence the error. You can either explicitly initialise Base in the Derived default constructor's initialisation list, or you can provide Base with a default constructor.

like this

Code:

Derived() : Base() {}

**csonx_p** · 03-16-2009

Originally Posted by csonx_p

like this

Code:

Derived() : Base() {}

k ...

Code:

Derived::Derived() : Base (5) {
}

**csonx_p** · 03-16-2009

Code:

#include <iostream> 

class Base {

public:
	Base ( int d ) { data = d;}
	void setData( int d ) { data = d;} 
	virtual void Show() = 0;
protected :
	int data;
};

class Derived : private Base {

public:
	Derived();
	void setData( int d ) { data = d; }
	void Show() { std::cout << "I'm showig off " << data << " in base"; }
};

Derived::Derived() : Base (5) {
}

void main () 
{
	Derived	d;	
	Base * b = &d;

	b->Show();
	d.setData(10);
	std::cout << "\n";
	b->Show();
}

error C2243: 'type cast' : conversion from 'Derived *__w64 ' to 'Base *' exists, but is inaccessible ???

thnx

**laserlight** · 03-16-2009

You are using private inheritance.

**csonx_p** · 03-16-2009

Originally Posted by laserlight

You are using private inheritance.

lol, forgot to remove tht... But gave me more knowledge .. thanx

**Elysia** · 03-16-2009

You are using void main. Why?

**csonx_p** · 03-16-2009

Originally Posted by Elysia

You are using void main. Why?

just for testing purposes? But now that you've asked, why not?

**laserlight** · 03-16-2009

Originally Posted by csonx_p

just for testing purposes? But now that you've asked, why not?

Because it is non-standard, and you have nothing to gain since changing void to int is enough.

**Elysia** · 03-17-2009

Originally Posted by csonx_p

just for testing purposes? But now that you've asked, why not?

As a member of this board, you should be fully aware that void main is frowned upon here (just see Salem's avatar).

**csonx_p** · 03-17-2009

Originally Posted by Elysia

just see Salem's avatar.

...

**dwks** · 03-17-2009

References about void main():

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