Re: [Vala] Using a C library

[Andrew Benton <andrew benton675 gmail com>]

Justin,

I believe that you have to use 
[CCode(cheader_filename="libspotify/api.h")] instead of cheader.

-Andrew

On 04/28/2015 06:29 PM, Justin Brown wrote:
> Hi Al,
>
> Thanks for the continued help. I've been making some progress on the vapi,
> but I've been putting off the compilation issue for a while now. Your reply
> had me go back to compiling the vapi properly instead of as a vala program.
> I think I'm still doing something slightly wrong. Structure:
>
> src/
> ├── fandingo.c
> ├── fandingo.vala
> └── vapi/
>      └── libspotify.vapi
> ibspotify --vapidir vapi/ fa
> The libspotify-devel RPM from rpmfusion comes with a spotify.pc. It's in a
> strange location, but that's fixed by exporting PKG_CONFIG_PATH. It's also
> named libspotify, so I renamed my vapi. Trying to compile:
>
> valac -v --pkg libspotify --vapidir vapi/ fandingo.vala
>
>
> The test program just tries to create an error enum, print the message, and
> print the spotify api version. I get a few errors:
>
> /home/justin/code/fandingo/src/fandingo.vala.c:48:2: error: unknown type
> name ‘sp_error’
>
>    sp_error err = 0;
>
>    ^
>
> /home/justin/code/fandingo/src/fandingo.vala.c:55:46: error:
> ‘SPOTIFY_API_VERSION’ undeclared (first use in this function)
>
>
> Seems like libspotify/api.h is not being linked correctly, which is
> strange.ibspotify --vapidir vapi/ fa
>
> vapi/libspotify.vapi begins with:
>
> [CCode (cheader = "libspotify/api.h")]
>
> namespace Spotify {
>
> That seems fine. However, if I generated C code with --ccode, the #include
> is missing:
>
> /* fandingo.c generated by valac 0.26.1, the Vala compiler
>   * generated from fandingo.vala, do not modify */
>
> #include <glib.h>
> #include <glib-object.h>
> #include <stdlib.h>
> #include <string.h>
> #include <stdio.h>
>
> If I add #include <libspotify/api.h>, and compile the generated C with the
> compilation command that valac provided earlier (cc -o
> '/home/justin/code/fandingo/src/fandingo'
> '/home/justin/code/fandingo/src/fandingo.c' -I/usr//include
> -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -L/usr//lib
> -lgobject-2.0 -lglib-2.0 -lspotify).
>
> Any idea why valac isn't adding "#include <libspotify/api.h>?"
>
> After the manual compilation, I think everything is resolved with the enum
> values. Errors 39-41 still produce "invalid error code" when calling
> sp_error_message, but I think that might mean that libspotify doesn't have
> error strings for those errors. The "jumps" (like 3 to 5 in my last email)
> are working properly. Hooray.
>
> Thanks,
> Justin
>
> On Tue, Apr 28, 2015 at 5:32 AM, Al Thomas <astavale yahoo co uk> wrote:
>
> > > From: Justin Brown <justin brown fandingo org>
> > > Cc: vala-list gnome org
> > > Sent: Wednesday, 22 April 2015, 7:05
> > > Subject: Re: [Vala] Using a C library
> > > I did have a question about the C sp_error enum. There are 36 values
> > [0-35] in the C library, but there are >some gaps such that the last value
> > (SYSTEM_FAILURE) is 41, not 35. Every once in a while in the C enum a
> > > manual value is specified that jumps the integer a few places -- for
> > example:
> > > SP_ERROR_TRACK_NOT_PLAYABLE        = 3,
> > > SP_ERROR_BAD_APPLICATION_KEY       = 5,
> > >
> > > I've tried a variety of solutions. If I don't specify any integer values
> > in Vala, then the codes don't >respect the "jumps," meaning that
> > SP_ERROR_BAD_APPLICATION_KEY == 4. If I specify the "jumps" or all the
> > > integers, then libspotify sp_error_message() complains about an invalid
> > type in a string (not a segfault or >compilation error). Why isn't Vala
> > using the C values properly when not specified? Also, what's the possible
> > > invalid type problem when specifying the integers? I don't feel like I'm
> > understanding whether it's a >int-length (unsigned/long/etc.) issue or
> > something else. Any idea why the Vala enum isn't pulling the values
> > > specified in libspotfiy/api.h?
> >
> > This is because you are not using a VAPI for your binding, but a Vala
> > program.
> >
> > As I understand it now, after some experimentation, a VAPI can be seen as a
> > translation file. It is used by the Vala compiler when it parses a Vala
> > program
> > to validate the identifier exists, in this case the Vala enum you have
> > created.
> >
> > The second thing the Vala compiler uses the VAPI file for is to generate
> > the C code
> > from the Vala program using the binding. So the cname CCode attribute will
> > translate the Vala program name for the enum to the C code name. The
> > cprefix CCode
> > attribute will prepend SP_ERROR_ to all the enum values in the C code.
> > What the
> > Vala compiler doesn't do is generate a C code translation of the enum in
> > the VAPI
> > itself. This is because the C code is already there in the C header file
> > of your
> > library. By placing the Vala enum in a VAPI you stop two versions of the
> > enum
> > being generated in C code.
> >
> > Hope that helps,
> >
> > Al
> > _______________________________________________
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