cvSetMouseCallback function pointer WinForms

edit

I got a function

void on_mouse(int event, int x, int y, int flag, void *param)
{
   //mouse functionality here
}

Then the function detectPositives() does the following command inside

cvSetMouseCallback(window_name, on_mouse, NULL);

And it doesn't seem to work using the function name as function pointer, which works perfectly in a CLI application, but not in this WinForm application header file.

Error message = error C3867: 'ObjectDetectionGUI::Form1::on_mouse': function call 
missing argument list; use '&ObjectDetectionGUI::Form1::on_mouse' to create a pointer 
to member

Anyone could help?