C g_signal_connect Passing data

main.c

#include <gtk/gtk.h>

typedef struct _a {
    gchar* msg;
    gint num;
} data;

void button_event(GtkWidget *widget, gpointer f) {
  data *d = f;
  g_print("%s %d\n", d->msg, d->num);
  d->num++;
}

int main(int argc, char** argv){
  // gtk init
  gtk_init(&argc, &argv);
  // create data
  data d;
  d.msg = "test";
  d.num = 0;
  // define widgets
  GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  GtkWidget *button = gtk_button_new();
  // connect signal
  g_signal_connect(button, "clicked", G_CALLBACK(button_event), &d);
  // add container
  gtk_container_add(GTK_CONTAINER(window), button);
  // show_all
  gtk_widget_show_all(window);
  // run
  gtk_main();
  return 0;
}