Re: [Vala] using a non-glib C library in vala

[Jan Hudec <bulb ucw cz>]

On Wed, Sep 16, 2009 at 10:33:22 -0400, Michael B. Trausch wrote:
> Mr. Maxwell, sorry for the dupe.  Forgot to cc the list.
>
> On Tue, 2009-09-15 at 17:14 -0500, Mr. Maxwell . wrote:
> > What do I do with the typedef struct declarations? This is what I have
> > but I don't think it's right.
> >
> > c code
> >   typedef struct { char _dummy; } ID3Tag;
> >
> > vala code
> >     [CCode(cname = "typedef struct")]
> >     public struct ID3Tag { private char _dummy; } 
>
> The type name for a non-typedef'd struct would be:
>
> struct struct_name
>
> Whereas the name for a typedef'd one is simply the name of the type.

That's correct. Except the bigger problem is, that it's not a struct.

Why? Well, because the real content of the struct is not defined, so it
cannot be passed by value -- which is a meaning of 'struct' in vala. It must
be passed by reference, which is signified by using 'class'.

> So, for example, let's say that we have a structure that contains a IP
> network address and could hold either an IPv4 or IPv6 address in C.
> This could look like:
>
> typedef enum _ip_address_type_t {
>   IP_ADDRESS_V4,
>   IP_ADDRESS_V6
> } ip_address_type_t;
>
> typedef struct _ip_address_t {
>   ip_address_type_t type;
>   unsigned char address[16];
> } ip_address_t;
>
> In Vala, this would be bound as (assuming this is in
> ip_address_type.h): 
>
> [CCode(cheader_filename = "ip_address_type.h",
>        cprefix = "",
>        c_lowercase_prefix = "")]
> namespace Native {
>   [CCode(cprefix = "IP_ADDRESS_")]
>   public enum IpAddressType {
>     V4,
>     V6
>   }
>
>   [CCode(cname = "ip_address_t")]
>   public struct IpAddress {
>     public IpAddressType type;
>     public uchar address[16];
>   }
> }
[...]
> However, there is one small problem:  You can *not* use the structure as
> a [SimpleType], due to a bug in Vala (see bug 588280).  If you attempt

Why do you think it is a [SimpleType]. SimpleTypes are only the built-in
non-structured types (int, char, float...) or anything typedefed to them
(size_t, ssize_t, time_t...). Anything defined using the struct keyword is
not one.

> to do so, Vala will generate an incorrect .c code file to feed to gcc,
> and gcc will (correctly) error out, stating that memset was not passed
> enough parameters.  This was deemed to be not a problem, though in my
> personal opinion, Vala should either throw an error or generate correct
> C code, not generate incorrect C code to be fed to the compiler.
>
> However, I don't know how to fix the issue in valac, so I can't really
> reopen the bug.  Just keep in mind that using a SimpleType-decorated
> struct is impossible in Vala, even if that is what you would do in C.

Vala should not generate invalid code, but this bug is indeed invalid as
described.

-- 
                                                 Jan 'Bulb' Hudec <bulb ucw cz>