Re: GObject get_property method copying string

Stephan,

On Thu, Aug 18, 2011 at 4:43 PM, Stefan Kost <[email protected]>wrote:

>
> On 08/11/11 13:52, Tiago Katcipis wrote:
> >
> >
> > Hi,
> >
> > I'm developing a library using GObject and I'm having trouble creating
> > a string property that does not makes a copy when g_object_get is
> > called. I used g_value_set_static_string to avoid the string from
> > being copied, but doing some debug it seems that g_object_get is
> > copying my string anyway.
> >
> > That is odd, because i see a lot of code using g_value_set_string on
> > get_property, and that would produce a completely useless additional
> > copy of the string (since g_object_get will copy it anyway).
> where is the extra copy being made in glib?
>

I'm not sure, but for example, i have the following get_property function:

static void
gsip_codec_info_get_property (GObject *object, guint prop_id, GValue *value,
GParamSpec *pspec)
{
    GSipCodecInfo * codec = GSIP_CODEC_INFO(object);

    switch (prop_id)
    {

    case PROP_CODEC_INFO_PAYLOAD:
            return g_value_set_static_string (value, codec->payload);
        break;

    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }
}

I expected that the returned string would be the same as codec->payload, but
on my tests, it is not, what i get when i call:

gchar * payload = NULL;

g_object_get (codec_info, "payload", &payload, NULL);

is a copy of codec->payload. I confirmed that freeing payload and unrefing
codec_info, it would result on a double free, but it actually works (also
printing the address of the pointers obviously shows that is a copy).

Doing more debug, i confirmed that g_value_set_static_string is not copying
the string (GValue holds the same gchar *), but something between there and
my g_object_get call is copying it.

Best regards,
Katcipis


> Stefan
> >
> > Sorry to bother with such a stupid question but the documentation just
> > says:
> >
> > "In general, a copy is made of the property contents and the caller is
> > responsible for freeing the memory in the appropriate manner for the
> > type, for instance by calling |g_free()|
> > <
> http://developer.gnome.org/glib/stable/glib/glib-Memory-Allocation.html#g-free
> >
> > or |g_object_unref()|
> > <
> http://developer.gnome.org/gobject/unstable/gobject-The-Base-Object-Type.html#g-object-unref
> >.
> > "
> >
> > What would be "in general" ? Do i have some control of it ? (i was
> > unable to find any) Am i understanding something wrong ?
> >
> > Best regards,
> > Katcipis
> >
> >
> > _______________________________________________
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> > [email protected]
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>
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