Virtual functions not working

Hello,

I have a class entitled "Layer" and a derived class entitled "Point". I have a pure virtual function in "Layer" entitled printLayer(). It is not defined in "Layer" although it is defined in "Point".

The program compiles OK, but when I try to build it I get "Unresolved External" errors.

Here is my code for the printLayer() in the "Layer" header:

Code:

virtual void printLayer(int);	//pure virtual function

and "Point" header:

Code:

virtual void printLayer(int);			//virtual function with definition

Here is the code for the printLayer() function in the "Point" defintion:

Code:

//begin printLayer
void Point::printLayer(int intArg)
{
	cout << "Point printLayer with argument " << intArg << " !" << endl;

}	//end printLayer

Here is my main program utilizing the classes:

Code:

#include <iostream.h>
#include "Layer.h"
#include "Point.h"

int main()
{
	//create a layer object and assign it to a layer pointer
	Layer * LayerPtr = new Point("aluspts_0.shp", "C:\\pec\\complete\\vector");
	
	int i = 2;
	LayerPtr->printLayer(i);

	delete LayerPtr;

	return 0;

}	//end main

Here are the error messages I receive upon using the build command. Note my main program is entitled "test.cpp":

Code:

test error LNK2001: unresolved external symbol "public: virtual void __thiscall Layer::printLayer(int)" (?printLayer@Layer@@UAEXH@Z)
test fatal error LNK1120: 1 unresolved externals

It appears the compiler is searching the "Layer" definitions for the printLayer() function. According to my documentation, a pure virtual function of an abstract base class requires no definition. The definition belongs in the derived class, which is "Point" in my case.

Why am I getting these error messages?

To declare a pure vitual function, you need to define it as NULL.

In your Layer class, define printLayer as:

virtual void printLayer(int) = 0;

Hope this helps.

That's it Thanks