Is PHP’s count() function O(1) or O(n) for arrays?

by

Well, we can look at the source:

/ext/standard/array.c

PHP_FUNCTION(count) calls php_count_recursive(), which in turn calls zend_hash_num_elements() for non-recursive array, which is implemented this way:

ZEND_API int zend_hash_num_elements(const HashTable *ht)
{
    IS_CONSISTENT(ht);

    return ht->nNumOfElements;
}

So you can see, it’s O(1) for $mode = COUNT_NORMAL.

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