On Tue, Mar 14, 2006 at 11:48:56AM +0200, Adrian Vasile wrote:
> I'm having trouble understanding the GHashTable and it's member
> functions.
GHashTable just stores some untyped pointers.
Since it has no idea what type the stored data are, it
cannot make a copies of them and does not make copies of
them. So...
> I've made the following simple code for testing purposes:
>
> #include <stdio.h>
> #include <glib.h>
>
> typedef struct _client
> {
> guint id;
> guint win;
> gchar *name;
> gchar *number;
> gboolean mute;
> } client ;
>
> static void print_hash_kv (gpointer key, gpointer value, gpointer
> user_data)
> {
> gchar *i = (gchar *) key;
> client *d = (client *) value;
>
> printf ("<-- %s -> %d , %s, %s in %d.\n", i, d->id, d->name, d->number,
> d->win);
> }
>
> int main (int argc, char **argv)
> {
> client *c, *d;
> GHashTable *hash = g_hash_table_new (g_str_hash, g_str_equal);
>
> if ((c = g_new (client, 1)) == NULL)
This cannot happen. g_new() aborts program when it fails to
allocate the memory.
> {
> printf ("unable to alloc c");
> return 1;
> }
>
> c->id = 2;
> c->win = 3;
> c->name = g_strdup ("client1");
> c->number = g_strdup ("0123456789");
> c->mute = TRUE;
>
> printf ("--> %d , %s, %s in %d.\n", c->id, c->name, c->number, c->win);
>
> g_hash_table_insert (hash, g_strdup ("2"), c);
I wonder who is going to free the key. Perhaps you intended
to use g_hash_table_new_full() and supply a key destroy
function? Or just get rid of the g_strdup() if keys are
constant strings.
> g_free (c);
Now the table contains a pointer to freed memory at key "2".
The c you freed here is the same chunk of memory as is
stored in the table. Remember, no copies, it just stores
some pointer.
> hash = g_hash_table_ref (hash);
I wonder what is this intended to mean. You already own
a reference to the hash table -- the initial one. And
I cannot see any g_hash_table_unref() here, so you will have
two *two* reference to the hash table to the end of program.
Why?
> if ((d = g_new (client, 1)) == NULL)
> {
> printf ("unable to alloc d");
> return 1;
> }
>
> d->id = 1;
> d->win = 2;
> d->name = g_strdup ("client2");
> d->number = g_strdup ("9876543210");
> d->mute = FALSE;
>
> printf ("--> %d , %s, %s in %d.\n", d->id, d->name, d->number, d->win);
>
> g_hash_table_insert (hash, g_strdup ("1"), d);
Again, the key is likely to be leaked.
> g_free (d);
Again, this makes the item at key "1" invalid (pointer to
freed memory).
> printf ("done inserting..... \n");
>
> g_hash_table_foreach (hash, print_hash_kv, NULL);
>
> return 0;
> }
>
> The thing is that the output is quite annoying:
> --> 2 , client1, 0123456789 in 3.
> --> 1 , client2, 9876543210 in 2.
> done inserting.....
> <-- 1 -> 0 , client2, 9876543210 in 2.
> <-- 2 -> 0 , client2, 9876543210 in 2.
The memory block orignially allocated for c (and then freed)
was reused for d. After d was freed too it was not reused
for anything else yet -- you'd get totally bogus values then.
> My question is how do I manage to get the hash table to actually give me
> back all the my inserts
Don't destroy them.
Yeti
--
That's enough.
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