对于数组，PHP 的 count() 函数是 O(1) 还是 O(n)? [英] Is PHP's count() function O(1) or O(n) for arrays?

问题描述

count() 真的计算所有的PHP 数组的元素，或者该值是否缓存在某处并被检索?

Does count() really count the all the elements of a PHP array, or is this value cached somewhere and just gets retrieved?

推荐答案

好吧，我们可以看看源码:

Well, we can look at the source:

/ext/standard/array.c

PHP_FUNCTION(计数) 调用 php_count_recursive()，它依次调用 zend_hash_num_elements() 用于非递归数组，其实现方式如下:

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;
}

所以你可以看到，对于 $mode = COUNT_NORMAL，它是 O(1).

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

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