Question

I’m wondering if it’s possible for a valid PHP Resource to have an ID of 0. I am getting database connection resources and so far they have all been non-zero positive integers. Just curious what the range of potential IDs is for resources.

Answer 1

The resource id may be in the range of an int. Search for “resource” or “ZEND_FETCH_RESOURCE” in the source code directory of PHP via the terminal. Then you’ll see the function:
(file ./Zend/zend_list.c, line 110)

ZEND_API void *zend_fetch_resource(zval **passed_id TSRMLS_DC, int default_id,
char *resource_type_name, int *found_resource_type, int num_resource_types, ...)

Inside the function, you’ll see that passed_id is the resource’s id and it’s of type int.
Normally, libraries pass a default id of -1, for example in file ./ext/mysql/php_mysql.c, line 1060.

In general you can assume that all the libraries will pass a real/exists resource id with value greater than 0, but that’s not a rule that every library must follow – it is possible to pass a negative resource id or 0.