RE: [PHP-DEV] Understanding the benefits of handling Bucket data in PHP's HashTables

Sorry for the formatting, I'm not sure why the newlines got removed since I formatted this much more nicely, any reason why it happened? I could repost it in a more readble format > From: jb_jeff@hotmail.com > To: internals@lists.php.net > Date: Thu, 16 Sep 2010 09:56:59 +0000 > Subject: [PHP-DEV] Understanding the benefits of handling Bucket data in PHP's HashTables > > > Hey guys (and girls), > I have been reading this list for sometimebut this is the first time I'm actually posting > something.This might fit better in a C\C++ forum but I base my question on the notion that I > confidence in my C skills and that there is an underlying cause for the choice of PHP developers to > save Bucket data the way they do.If I am mistaken in posting this here please let me know. > I came to ponder this when working with hash functions (zend_hash_find,zend_hash_add) and I saw > that zend_hash_add (macro for _zend_hash_add_or_update) accepts pData as void * but is usually > passed an address of a pointer like in: > zend_class_entry *ce;zend_hash_add(CG(class_table), "class_name",class_length+1, > &ce); > pData is in turn memcpy'd into a Bucket's pData element which is also void *, passing > the &ce suggests that what will get memcpy'd will be the contents of &ce which is in > turn the address pointed to by ce, the address of a zend_class_entry struct, this suggests that the > Bucket's pData element though marked as void * actually servs as a void ** (since it points to > an adress which should be dereferenced as a pointer). > I validated this by looking at zend_hash_find which accepts pData as void **, this time pData > is to hold the address for the data retrieved by zend_hash_find, this time I noticed the function > call to be : > zend_class_entry **ce;zend_hash_find(CG(class_table), "class_name", class_length+1, > (void **) &ce); > and the data assigned to pData is :*pData = Bucket->pData; > By my logic by setting *pData I am setting the data held at the address in pData itself which > is &ce, this sets ce to point to an address of Bucket->pData which as I established earlier > is used as a void **. > I may be missing some basic understanding in pointers but I am pretty confident that this is > not the case and thus I am asking is there a specific reason to use this sort of > 'trickery' instead of of explicitly using void *, I fail to see the harm in > Bucket->pData being a pointer to the data itself and the needed casts to be done instead of the > current situtaiton where it points to another address. > Thank you for any light you can shed on this. >