MSVC error I get the error: ''blabla'' uses undefined class ''Blabla''. The situation is this that I have one header where I define the class Blabla. I have another class in another header that has an instance of the class Blabla and this is the point the error is pointing to. I wrote this code to see if I got the error and I did (it can''t be linked but that tdoesn''t matter):

    class num2;

class num1
{
public:
	num2 n;
	int metod(void);
};

class num2
{
public:
	num2(void);
	int fff(void);
};

int num2::fff(void)
{
	return 1;
}

void main(void)
{	
}    

What causes the error?

did you #include the header containing the definition of Blabla in the header containing the instance?

If you''re declaring a non-pointer member of a class you must have its full definition before that declaration. You need to cut the definition of "num2" and paste it above the definition of "num1."