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

[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



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