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Date: Mon, 9 Sep 2019 13:33:14 +0200
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To: PHP internals <internals@lists.php.net>
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Subject: Re: FFI extension / NULL-Checks
From: phofstetter@sensational.ch (Philip Hofstetter)

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In response to these findings so far, I have now submitted

https://github.com/php/php-src/pull/4691

that adds an FFI::isNull() method that returns true if the passed CData
instance points to NULL.

If you agree that something like this is indeed needed, I will gladly
update the PR and add unit tests.

Philip

On Mon, Sep 9, 2019 at 8:03 AM Philip Hofstetter <phofstetter@sensational.c=
h>
wrote:

> 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 !=3D NULL){
>    do_error_handling();
> }
>
> If I translate this to PHP FFI, I would do
>
> $err =3D $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)
> $err[0] !=3D null
> -> is always true, regardless of whether func as assigned an error or not
>
> isset($err->{0})
> isset($err[0])
> -> Cannot use object of type FFI\CData as array
>
> $err->{0} !=3D NULL;
> -> FFI\Exception: NULL pointer dereference
>
> $err[0];
> -> segfault
>
> I'm sure I must be doing something wrong, but I don't know what. Also, th=
e
> documentation could do with an example on how to achieve the desired resu=
lt
> and, TBH, I think some of the various attempts produce a somewhat
> unexpected output.
>
> Any comments?
>
> Philip
>
>
> var_dump(isset($r->{0}));
> -> Error:  Cannot use object of type FFI\CData as array
>
> $a =3D '{0}';
> var_dump(isset($r->$a));
> -> Error:  Cannot use object of type FFI\CData as array
>
>
>     var_dump(isset($r[0]));
>     var_dump($r[0]);
>
>
>

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