Question

I just thought I would comb through this to find the answer:
http://svn.php.net/viewvc/php/php-src/

But I couldn’t find it. In C++ <map> is implemented as a balanced binary search tree with const key values. this is nice, you get O(log n) search, insert, delete, etc runtimes. O(n) enumeration time.

What I’m wondering is the underlying data structure of PHP arrays. There are a few SO posts on PHP arrays that say “well they do pretty much the same thing, so don’t worry about it!”. not what I’m after. Is it O(1) (hash table) or O(log n) (balanced binary tree) lookup? (for example)

If anyone can help me out or point me to the right PHP C source file, that would be awesome (though a little explanation would be good – I’m really bad at C). Or if you just have cool insights about PHP arrays that’s good as well – I’m trying to understand the entire underlying data structure.

Answer 1

An array in PHP is actually an ordered map. A map is a type that
associates values to keys. This type is optimized for several
different uses; it can be treated as an array, list (vector), hash
table (an implementation of a map), dictionary, collection, stack,
queue, and probably more. As array values can be other arrays, trees
and multidimensional arrays are also possible.

The implementation is in fact some sort of a HashTable.

-> http://php.net/manual/en/language.types.array.php
-> How is the PHP array implemented on the C level?