Re: [Vala] Why does a simple struct need a special copy function?

[Jonas Kulla <nyocurio gmail com>]

2013/7/12 Nadav Vinik <nadavvin gmail com>

> On 6 July 2013 22:06, Jonas Kulla <nyocurio gmail com> wrote:
>
> > 2013/7/6 Nadav Vinik <nadavvin gmail com>
> >
> > > On 6 July 2013 11:15, Jonas Kulla <nyocurio gmail com> wrote:
> > >
> > > > 2013/7/6 Nadav Vinik <nadavvin gmail com>
> > > >
> > > > >  Hello
> > > > >
> > > > > I get an error:
> > > > > undefined reference to `pcap_packet_header_copy'
>
> I try to write the missing copy function:
>
> public void pcap_packet_header_copy(PCap.packet_header source,
> PCap.packet_header dest) {
>     dest = PCap.packet_header();
>     dest.ts = source.ts;
>     dest.caplen = source.caplen;
>     dest.len = source.len;
> }
>
> but I get an error:
> error: Invalid assignment from owned expression to unowned variable
>     dest = PCap.packet_header();
>     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
> if I do:
> dest = (owned)PCap.packet_header();
>
> I get an error:
> error: Reference transfer not supported for this expression
>
> What should I do?
>
> thanks
> Nadav
>
>
> > > > > why can't vala copy? it's not only allocate memory of size of the
> > > > > struct
> > > > > and copy it to it?
> > > > >
> > > > >
> > > > > struct pcap_pkthdr {
> > > > >     struct timeval ts;    /* time stamp */
> > > > >     bpf_u_int32 caplen;    /* length of portion present */
> > > > >     bpf_u_int32 len;    /* length this packet (off wire) */
> > > > > };
> > > > >
> > > > > [CCode(cname = "struct pcap_pkthdr", has_type_id = false,
> > > > > destroy_function
> > > > > = "")]
> > > > >     public struct packet_header {
> > > > >         Posix.timeval ts;
> > > > >         int32 caplen;
> > > > >         int32 len;
> > > > >     }
> > > > >
> > > > > thanks
> > > > > Nadav
> > > > > _______________________________________________
> > > > > vala-list mailing list
> > > > > vala-list gnome org
> > > > > https://mail.gnome.org/mailman/listinfo/vala-list
> > > >
> > > > Hi,
> > > >
> > > > I assume that declaration is from one of your vapis?
> > > > Vala always requires copy functions for structs, because
> > > > gobject is oblivious to the contents of your structs.
> > > > A simple example such as
> > > >
> > > > struct MyStruct {
> > > >   int a;
> > > >   string b;
> > > > }
> > > >
> > > > demonstrates why you can't simply shallow memcpy them.
> > > > For structs defined within vala code, valac generates all necessary
> > > > functions for you, but if you're interfacing with other C libs,
> > > > these need to be manually provided.
> > > >
> > > > Can you try adding "has_copy_function = false" to
> > > > the struct attributes?
> > >
> > > I tried, it compile, but than I have segmentation fault.
> > >
> > >
> > > > Jonas
> > >
> > >
> > >
> > > --
> > > הבלוג שלי:
> > > http://nadavvin.com
> >
> > Uhh, do you know how to debug programs width gdb?
> > It's pretty hard to tell from that what is going on.
> >
> > Jonas
>
>
>
> --
> הבלוג שלי:
> http://nadavvin.com


AFAIK the 'copy' function isn't responsible for allocating a new instance.
You should treat the 'dest' object as already allocted. Have you tried
without
that first problematic line in your function?

Jonas