Re: memory problem ?

[Thomas Mailund <mailund mailund dk>]

On Mon, 2001-09-10 at 09:54, danilo lujambio wrote:
> Hi, my english is no enough but I will try
>
>
> in a program I declare a global variable :
>
> gchar *id_cabina_global;
> ........
> .......
>
> in main I allocate :
>
> main( )
> {
> ..........
> id_cabina_global = (gchar *)g_malloc(sizeof(LEN_CABINA));
> .......
> }
> in some place :
>
>  id_cabina_global = aux;

here you're re-assigning id_cabina_global, and thus loosing your
reference to the buffer allocated in main()

> in one callback function that I use, which creates a new frame with
> information
>
> reporte_dialog()
> {
>
>   GtkWidget *hbox_freporte;
>   GtkWidget *vbox_freporte;
>
> ........................
>
> then I need to use
>
> id_cabina_global
>
> and the value is strange ( not the assigned previously)
>
> but if I make :
>
> if ((hbox_freporte = (GtkWidget *)malloc(sizeof(GtkWidget)) == NULL))
>       {
>      g_print(".....");
>      exit(0);
>       }
>
>     if ((vbox_freporte = (GtkWidget *)malloc(sizeof(GtkWidget)) ==
> NULL))
>       {
>      g_print("........");
>      exit(0);
>       }

why are you malloc-ing GtkWidgets? These are usually allocated through
their constructors (_new() functions).

> the id_cabina_global value is OK .
>
> Why ?

It's hard to say. When you malloc you mess around with the free-lists
and stuff, but that really shouldn't affect a global pointer, nomatter
what it points to. Now as to changing the thing that it points to, (not
the address but the data there), malloc-ing could easily return a buffer
from inside there, and even if you don't access the returned memory
buffer, the messing around with free-lists could easily change what you
are pointing at.

> why I need to use malloc in vbox_freporte and hbox_freporte to preserve
> id_cabina ?

you shouldn't.

> sorry if my question is stupid but I can't understand the root of
> problem

neither can I...perhaps if you track all assignments to the variable,
and print some output about before/after states you would know if it is
changed there. If not, something else is probably pointing the the same
buffer as id_cabina_global and the problem is there.

        /mailund

-- 
And out of the chaos, a voice spoke:
"Smile and be happy, for it can always be worse".
And I smiled, and I was happy, and it did get worse.