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Date: Mon, 12 Mar 2018 13:18:30 -0400
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To: Richard Klingler <richard@klingler.net>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Migrating php extension from 5 to 7, ZVAL_STRINGL no
 value returned
From: pollita@php.net (Sara Golemon)

On Mon, Mar 12, 2018 at 12:16 PM, Richard Klingler <richard@klingler.net> wrote:
> ZEND_FUNCTION(readmydevice)
> {
>         zend_long n;
>         zval *z;
>         size_t len;
>         char *p;
>         long r;
>
>         if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "lzl", &n,
> &z, &len) == FAILURE) {
>                 return;
>         }
>
>         p = (char *) emalloc(len + 1);
>         memset(p,0,len+1);
>
>         r = myread(n, p, len);
>         printf("Read %d bytes from device %d up to %d bytes\n", mycount,
> n, len);
>         p[ibcnt] = '\0';
>         ZVAL_STRINGL(z, p, mycount);
>         printf("Returned %s\n", p);
>         efree(p);
>         RETURN_LONG(r);
> }
>
>
> Any ideas why ZVAL_STRINGL is not doing anything?
> Or did I miss something?
>
Well, ZVAL_STRINGL is probably doing something, but there are two
reasons there's no way to be certain:

1. What is 'mycount' and where does it come from / how is it set?  If
it's zero, then you'll be saving a zero length string. In any case, it
doesn't seem to have any relationship to the data read into `p`.  I'm
guessing you wanted to use `r` rather than `mycount` both here and in
your debug message.

2. I'm inferring that you want argument 2 to your function to be a
pass-by-ref argument.  Are you specifying any arg_info in the function
entry list? (where you have your PHP_FE macro -- or perhaps ZEND_FE
macro, since you seem to be using those versions).  In order to pass
by ref, you need that structure to specify that the argument is
by-ref.  This *might* have worked without it in PHP 5, but only by
accident and would have probably failed in hard-to-diagnose ways.

2a. Also, when using by-ref args, you need to destruct any previously
held value.  In this case, with a zval_dtor(z); prior to the
ZVAL_STRINGL() macro.

-Sara