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Newsgroups: comp.lang.ada
Date: Mon, 25 Mar 2019 09:42:12 -0700 (PDT)
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Subject: Re: differences between Ada and C in gnat forcing me to use C instead
 of Ada
From: matthewbrentmccarty@gmail.com
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Xref: reader01.eternal-september.org comp.lang.ada:55956
Date: 2019-03-25T09:42:12-07:00
List-Id: <comp.lang.ada>

Hi all:

I don't know.  I chose 5 elements in the array since I only have 1 scanner =
attached to my system.  I wasn't sure how to make it null terminated. I tri=
ed:

nul_sane_device_ptr : constant Sane_Device_Ptr :=3D null;
devices :  aliased  Device_Array (1..5) :=3D (others =3D> nul_sane_device_p=
tr );


In my C example which works, I have a header that says:

#define NELEMS(x)  (sizeof(x) / sizeof((x)[0]))
void sane_print_devices (const SANE_Device ** device_list);


and then C code which does the following:

const SANE_Device	**device_list;

status =3D sane_get_devices (&device_list, SANE_TRUE);
sane_print_devices (device_list);

I thought &device_list was the same as "devices(1)'Address" in Ada.

Regards,
Matthew McCarty

PS:

There's a html file at http://www.sane-project.org/html/doc012.html that sa=
ys:

4.3.3 sane_get_devices

This function can be used to query the list of devices that are available. =
If the function executes successfully, it stores a pointer to a NULL termin=
ated array of pointers to SANE_Device structures in *device_list. The retur=
ned list is guaranteed to remain unchanged and valid until (a) another call=
 to this function is performed or (b) a call to sane_exit() is performed. T=
his function can be called repeatedly to detect when new devices become ava=
ilable. If argument local_only is true, only local devices are returned (de=
vices directly attached to the machine that SANE is running on). If it is f=
alse, the device list includes all remote devices that are accessible to th=
e SANE library.

    SANE_Status sane_get_devices (const SANE_Device *** device_list,
                                  SANE_Bool local_only);

This function may fail with SANE_STATUS_NO_MEM if an insufficient amount of=
 memory is available.

    Backend Implementation Note
    SANE does not require that this function is called before a sane_open()=
 call is performed. A device name may be specified explicitly by a user whi=
ch would make it unnecessary and undesirable to call this function first.=
=20