GTK implementation of MessageBox

Hmm, ok. I’d suggest code like this, then:

typedef struct {
    int type;
    int result;
} DialogData;
    
static gboolean
display_dialog(gpointer user_data)
{
    DialogData *dialog_data = user_data;
    GtkWidget *dialog;
    
    if (dialog_data->type & MB_YESNO)
        dialog = gtk_message_dialog_new(...);
    else
        dialog = gtk_message_dialog_new(...);
    
    // Set title, etc.
    
    dialog_data->result = gtk_dialog_run(...);
    
    gtk_main_quit();  // Quits the main loop run in MessageBox()
    
    return FALSE;
}
    
int MessageBox(...)
{
    DialogData dialog_data;
    
    dialog_data.type = type;
    
    gtk_idle_add(display_dialog, &dialog_data);
    
    gtk_main();
    
    // Do stuff based on dialog_data.result
}

The struct is required because you need to pass around a couple pieces of data. The gtk_idle_add() call adds a method to be run when the main loop is running and idle, and the FALSE return value from the display_dialog() call means that it’s only run once. After we get the result from the dialog, we quit the main loop. That’ll cause the gtk_main() in your main MessageBox() method to return, and you’ll be able to access the result from there.