Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:106910
MIME-Version: 1.0
Date: Mon, 9 Sep 2019 08:03:32 +0200
Message-ID: <CAGKNXQEaC1DajOogF98iq=PL-MvOom43kK_JPpREYrQQ_o_KYA@mail.gmail.com>
To: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000d326a00592188c95"
Subject: FFI extension / NULL-Checks
From: phofstetter@sensational.ch (Philip Hofstetter)

--000000000000d326a00592188c95
Content-Type: text/plain; charset="UTF-8"

Hello,

(I'm writing to the internals list because I don't think that at this
point, FFI usage is wide-spread enough to get an opinion on other venues)

maybe I'm just stupid, but I think there has been a slight oversight in the
API design for the FFI interface.

My problem is with functions that return a pointer to a struct as an out
parameter.

So in C, it would look like this:

Error* err;
func(&err);

if (err != NULL){
   do_error_handling();
}

If I translate this to PHP FFI, I would do

$err = $ffi->new("Error*");
$ffi->func(FFI::addr($err));

if I `var_dump` $err, I do see a public {0} property be set to NULL or to
actual error data.

My issue is though: How do I check whether err* as been assgined to?

isset($err)
$err[0] != null
-> is always true, regardless of whether func as assigned an error or not

isset($err->{0})
isset($err[0])
-> Cannot use object of type FFI\CData as array

$err->{0} != NULL;
-> FFI\Exception: NULL pointer dereference

$err[0];
-> segfault

I'm sure I must be doing something wrong, but I don't know what. Also, the
documentation could do with an example on how to achieve the desired result
and, TBH, I think some of the various attempts produce a somewhat
unexpected output.

Any comments?

Philip


var_dump(isset($r->{0}));
-> Error:  Cannot use object of type FFI\CData as array

$a = '{0}';
var_dump(isset($r->$a));
-> Error:  Cannot use object of type FFI\CData as array


    var_dump(isset($r[0]));
    var_dump($r[0]);

--000000000000d326a00592188c95--