Re: [gtk-list] GTK_ENTRY cast segfaults, I think

[Jeroen Benckhuijsen <jeroen benck demon nl>]

Ron Martin wrote:
> 
> Hello.
> 
> I have a window that has several GtkEntry widgets.  I store pointers to
> those widgets in a GList, and attach the Glist as object data with
> gtk_set_object_data.  When the callback funtion for the "Okay" button is
> clicked, a callback funtion is called that gets the GList from the
> widget data and goes through each element, storing the text in the entry
> widgets pointed to by the data in the GList.  However, I get a
> segmentation fault whenever I click "Okay". gdb says:
> 
> (gdb) backtrace
> #0  0x400fae10 in gtk_type_check_object_cast ()
> #1  0x804dbcb in register_new_conn (widget=0x8078fb0, event=0x0,
>     data=0x40137018) at callbacks.c:58
> #2  0x400a7b4d in gtk_marshal_NONE__NONE ()
> #3  0x400d4fdd in gtk_handlers_run ()
> #4  0x400d4422 in gtk_signal_real_emit ()
> #5  0x400d2575 in gtk_signal_emit ()
> #6  0x401078c8 in gtk_widget_activate ()
> #7  0x4010ee24 in gtk_window_key_press_event ()
> #8  0x400a7719 in gtk_marshal_BOOL__POINTER ()
> #9  0x400d445b in gtk_signal_real_emit ()
> #10 0x400d2575 in gtk_signal_emit ()
> #11 0x4010777c in gtk_widget_event ()
> #12 0x400a75f6 in gtk_propagate_event ()
> #13 0x400a68ca in gtk_main_do_event ()
> #14 0x4015100b in gdk_event_dispatch ()
> #15 0x4017fbe6 in g_main_dispatch ()
> #16 0x401801a1 in g_main_iterate ()
> #17 0x40180341 in g_main_run ()
> #18 0x400a6209 in gtk_main ()
> #19 0x804a477 in main (argc=1, argv=0xbffffbf4) at main.c:51
> #20 0x4029ecb3 in __libc_start_main (main=0x804a410 <main>, argc=1,
>     argv=0xbffffbf4, init=0x8049ca8 <_init>, fini=0x804e1cc <_fini>,
>     rtld_fini=0x4000a350 <_dl_fini>, stack_end=0xbffffbec)
>     at ../sysdeps/generic/libc-start.c:78
> 
> And here is a brief portion of the code:
> 
>         GtkWidget * entry_temp;
>         GList * list;
> 
>         list = (GList *)gtk_object_get_data(GTK_OBJECT(widget), "entries");
> 
>         input_info = (struct conn_info *)malloc(sizeof(info_database));
>         bzero(input_info, sizeof(info_database));
>
>         entry_temp = (GtkWidget *)g_list_nth_data(list, 0);
> /* line 58 */ g_print("%s\n", gtk_entry_get_text(GTK_ENTRY(entry_temp));
> 
> Do I need to allocate memory for entry_temp?  The fault seems to occur
> in the GTK_ENTRY macro, which is why I think this.
> 

Segfault means your accessing memory you're not permitted to access.
Your problem is probably that the pointer stored in entry_temp is not
the pointer you want (the pointer to the entry-data). It will probably
just contain nonsense. Solution: check you're code where the pointer is
assigned, write it down, and compare it with the pointer you retrieve.
If they differ, you did something wrong, what is hard to say without the
code... 

Also i think this code is very weird. You alloc memory for a
info_database and store
it in an other type of structure....

        input_info = (struct conn_info *)malloc(sizeof(info_database));
        bzero(input_info, sizeof(info_database));

Also you may want to add a check wheter the allocation was succesful
(input_info != NULL) or you'll get a segfault when the allocation fails.
Using g_malloc() solves this problem, but it exists you're app when it
fails, depends on you're choices..

Jeroen