Unable to pass argument to GTK callback - c++

Question

When the program is initially run, the print statements, print a valid hex code corresponding to the pointer. However, when I click on the screen, and the handleClick method is called through the 'clicked' callback, 0x0 is printed to the screen. What happened? Why has my board object suddenly become null?
#include <stdio.h>
#include <stdlib.h>
#include <gtk/gtk.h>
#include "board.h"
void printBoard(Board *board);
void handleClick(GtkWidget *widget, GdkEventButton *event, cairo_t *cr, gpointer data);
gboolean draw_cb(GtkWidget *widget, cairo_t *cr, gpointer data)
{
Board *temp = (Board *)data;
printf("%p\n",temp);
return TRUE;
}
void handleClick (GtkWidget *widget, GdkEventButton *event, cairo_t *cr, gpointer data)
{
Board *temp = (Board *)data;
printf("%p\n",temp);
}
void start(Board *newBoard)
{
GtkWidget *window;
GtkWidget *da;
GtkWidget *frame;
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
char string[40];
snprintf(string, sizeof(string), "Connect %d-%d",newBoard->k,newBoard->n);
gtk_window_set_default_size (GTK_WINDOW(window), 400, 400);
gtk_window_move(GTK_WINDOW(window), 100, 100);
g_signal_connect (GTK_WINDOW(window), "destroy", G_CALLBACK (gtk_main_quit), NULL);
da = gtk_drawing_area_new ();
gtk_widget_set_size_request (da, 500, 500);
frame = gtk_frame_new (NULL);
gtk_frame_set_shadow_type (GTK_FRAME (frame), GTK_SHADOW_IN);
gtk_container_add (GTK_CONTAINER (window), frame);
gtk_container_add (GTK_CONTAINER (frame), da);
gtk_widget_set_events (da, gtk_widget_get_events (da)
| GDK_BUTTON_PRESS_MASK);
g_signal_connect (da, "draw",
G_CALLBACK (draw_cb), newBoard);
g_signal_connect (da, "button-press-event",
G_CALLBACK (handleClick), newBoard);
gtk_widget_show_all (window);
}

Answer 1

The prototype of the button-press-event signal handler is the following according to the reference manual.
gboolean user_function (GtkWidget *widget,
GdkEvent *event,
gpointer user_data)
If you remove cairo_t *cr parameter from the handleClick function data will be ok.

Answer 2

As Szilard said, you're using the wrong prototype for the handleClick function.
The button-press-event signal handler has the following prototype:
gboolean user_function (GtkWidget *widget,
GdkEvent *event,
gpointer user_data)
To fix your mistakes, you need to:
remove thecairo_t *cr parameter. It was receiving the value of data.
fix event type which is GdkEvent *, not GdkEventButton *
fix the return value, which is a boolean, not void, and which is important to determine if the event is propagated or not.