Re: Some question about GLib

[Colomban Wendling <lists ban herbesfolles org>]

Le 25/07/2014 23:46, Ameen Sayegh a écrit :
> [...] and I'm interested in C Language and its simplicity

I'm afraid that's not completely true :)

> [...]
>
> I have some question about the source code that I don't know what it
> does mean for example:
> gmem.h:120: "(void) (0 ? (gpointer) *(pp) : 0);"

That's a hack to catch misuses of the g_clear_pointer() macro.  See
https://bugzilla.gnome.org/show_bug.cgi?id=674634#c34

The idea is that if pp is a pointer and not a pointer to pointer, each
branch of the conditional expression will have a different type and this
is invalid -- hence the compiler will error-out.

To take Xavier's example, imagine the following code:

        struct { gpointer x; } test;
        g_clear_pointer(&test);

The first static assertion in g_clear_pointer() (which is (sizeof *(pp)
== sizeof (gpointer))) won't catch it as the struct has the size of a
gpointer, so it would go unnoticed.  Therefore, there is this second
hack to make sure to catch this.

Regards,
Colomban