Question

I’ve stumbled upon an interesting case while developing an extension for PHP. In the extension code I have:

PHP_FUNCTION(foo)
{
   ....
   php_debug_zval_dump(return_value, 1);
}

In the PHP code:

$v = foo();
debug_zval_dump($v);

When running the above, I get:

string(19) "Mouse configuration" refcount(1)
NULL refcount(2)

What can be the reason that the value isn’t passed properly from the extension?

Thanks!

Answer 1

It’s not that strange.

For instance, if you did return_value = some_string_zval; you would be changing only the local variable. php_debug_zval_dump would work, but it would have no effect outside the function. You have to actively copy the zval, e.g. with:

ZVAL_COPY_VALUE(return_value, my_string_zval_p);
zval_copy_ctor(return_value);

The only case you could return from an internal function merely copying a pointer instead of copying data was if that function returned by reference. In that case, you’re given a zval**.