Here's my understanding of why each pointer is needed, from reading the Zend source code for a while:
1) The innermost pointer is needed because Zend hash tables actually store a "zval* " (pointer to zval), not a zval directly. The zval is allocated separately, then its pointer is stored into the table.
2) The second pointer is needed because Zend tables internally malloc storage for whatever they store (zval* ) in this case, then access that data as a pointer. The "zval* " pointer is memcpy'd into the malloc'd area. This data is accessed through a "zval* * " pointer. This allows users of zend_hash_xxx to not only access the "zval* " pointer, but also change it.
3) In C, one way for a function to return a value is by passing a pointer to a variable that will store the result. Since zend_hash_find returns the internal "zval* * " data, you need to pass in a "zval* * * " pointer to a "zval* * " pointer that is the actual return value you want. Through this "zval* * " pointer, you can read and also change the "zval* " data stored in that hash table cell.
1) Symbol tables store double pointer, not single, see my comment to the parent for the reason why. There may be hash tables that store single pointers, but not symbol tables.
1) The innermost pointer is needed because Zend hash tables actually store a "zval* " (pointer to zval), not a zval directly. The zval is allocated separately, then its pointer is stored into the table.
2) The second pointer is needed because Zend tables internally malloc storage for whatever they store (zval* ) in this case, then access that data as a pointer. The "zval* " pointer is memcpy'd into the malloc'd area. This data is accessed through a "zval* * " pointer. This allows users of zend_hash_xxx to not only access the "zval* " pointer, but also change it.
3) In C, one way for a function to return a value is by passing a pointer to a variable that will store the result. Since zend_hash_find returns the internal "zval* * " data, you need to pass in a "zval* * * " pointer to a "zval* * " pointer that is the actual return value you want. Through this "zval* * " pointer, you can read and also change the "zval* " data stored in that hash table cell.