Thread: Freeing dynamic allocated memory of structure

Hello guys, I have qusetion, I have following structure:

Code:

typedef struct
{
	GtkWidget* PoziomaLinijka; <--GTK
	GtkWidget* PionowaLinijka; <--GTK
	GtkWidget* Label1; <--GTK
	GtkWidget* Label2; <--GTK
	gint x,y; <--GTK
} StrukturaDrawing;

And now I dynamicly allocate memory for it:

Code:

StrukturaDrawing* Wsk;
  Wsk = (StrukturaDrawing*)malloc(sizeof(StrukturaDrawing));
  if (!Wsk)
  {
	std::cout << "Error" << std::endl; 
  }

It works great, it allocates it. Now I use GTK callbacks to do stuff with it, which works great but when I want to free memory of it:
Callback to function: Wyjscie:

Code:

 g_signal_connect(G_OBJECT(Okno), "destroy", G_CALLBACK(Wyjscie), Wsk);

Code:

void Wyjscie(GtkWindow* window, GdkEvent* event, StrukturaDrawing* data)
{
	gtk_main_quit();
	free(data);
	data = NULL;
}

I get:
First-chance exception at 0x7c96df51 in Ekseprymetnowanie.exe: 0xC0000005: Access violation reading location 0xfffffff9.

But if I write data = NULL and then free(data) which is nonsense, right? I get no warnings, also if I comment out freeing memory I get no error but then I will get memory leaks.

Thanks in advance guys.