While working with static class i got this error. 

Linking...
FTP.obj : error LNK2001: unresolved external symbol "public: static struct HWND__ 
* FTP::hFTPWind" (?hFTPWind@FTP@@2PAUHWND__@@A)
LeedharFTP.obj : error LNK2001: unresolved external symbol "public: static struct 
HWND__ * FTP::hFTPWind" (?hFTPWind@FTP@@2PAUHWND__@@A)
Debug/LeedharFTP.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

LeedharFTP.exe - 3 error(s), 0 warning(s)



This is how I fixed it 

The problem was when u declare a member variable as static u have to intitlize 
it globally before using it . Here's some info i got from this site. 

http://www.functionx.com/vcnet/keywords/static.htm


In C++, you must first declare a variable before using it. The C++ language provides an
 exception to this rule through the static  keyword. If you declare a member variable as 
static in a class, an instance of that class would be made available when the class is used.

If you declare a member variable of a class as static, in C++, you must initialize it 
globally before using the static member variable. Here is an example:


#include <iostream>

using namespace std;



class CSquare

{

public:

	static double Side;

	CSquare() {};

	void setSide(double S) { Side = S; }

	double getSide() { return Side; }

	double Area() { return Side * Side; }

};



double CSquare::Side = 30.65;



int main()

{

    	// TODO: Please replace the sample code below with your own.

	CSquare Sqr;



	cout << "Square Characteristics";

	cout << "nSide: " << CSquare::Side;

	cout << "nArea: " << Sqr.Area() << endl;



	Sqr.setSide(44.28);



	cout << "nSquare Characteristics";

	cout << "nSide: " << CSquare::Side;

	cout << "nArea: " << Sqr.Area();



    	cout << "n";

	return 0;

}



This would produce:



Square Characteristics

Side: 30.65

Area: 939.422



Square Characteristics

Side: 44.28

Area: 1960.72

Press any key to continue



Notice that, in the above class, we declared the static member variable public, which is 
sometimes considered bad programming. If you decide to "hide" a member variable in a 
private section, then you should create a method that would allow the "external world" 
to access the member variable.




Besides a static method that serves as intermediary between a static member variable and other 
classes, you can use as many methods as you judge necessary. Here is an example:



#include <iostream>

using namespace std;



class CSquare

{

private:

	static double Side;

public:

	CSquare() {};

	static void setSide(double S) { Side = S; }

	static double getSide() { return Side; }

	static double Area() { return Side * Side; }

};



double CSquare::Side = 30.65;



int main()

{

    	// TODO: Please replace the sample code below with your own.

	CSquare Sqr;



	cout << "Square Characteristics";

	cout << "nSide: " << CSquare::getSide();

	cout << "nArea: " << Sqr.Area() << endl;



	Sqr.setSide(44.28);



	cout << "nSquare Characteristics";

	cout << "nSide: " << CSquare::getSide();

	cout << "nArea: " << Sqr.Area();



    	cout << "n";

	return 0;

}



The result is the same as above