What's the behavior of count when array has more than 2147483647 elements?

On a 32-bit system, an array can have as much as 4294967295 elements (as per Artefacto's post on another thread).

However, count returns the number of elements as an int, and on a 32-bit system, an int is at most 2147483647.

What will count return when an array has more than 2147483647 elements?

Solution

First of all, based on the size of an array element, you would need at least 163 GiB (32-bit) or 309 GiB (64-bit) of memory before you can observe this behaviour.

The return value of count() is based on zend_hash_num_elements():

ZEND_API int zend_hash_num_elements(const HashTable *ht)

This return value then gets cast into a long before it's returned to your code; this causes count() to return a seemingly negative value. This can be fixed by forcing it back into an unsigned value:

$c = count($array_with_pow_2_32_elements);
echo $c; // -2147483648
printf("%u\n", $c); // 2147483648

Or:

$c = sprintf('%u', $c);
echo $c; // 2147483648