To use apcu, the apcu extension has to be installed. You can find it here https://pecl.php.net/package/APCu

Note: apcu is not the same as apc! 

APCu is the official replacement for the outdated APC extension. APC provided both opcode caching (opcache) and object caching. As PHP versions 5.5 and above include their own opcache, APC was no longer compatible, and its opcache functionality became useless. The developers of APC then created APCu, which offers only the object caching (read "in memory data caching") functionality (they removed the outdated opcache).

Wondering how to use apcu? The following example should give you a basic understanding.

<?php

date_default_timezone_set('Europe/Amsterdam');

$apcuAvailabe = function_exists('apcu_enabled') && apcu_enabled();

if($apcuAvailabe)
{
    //apcu_clear_cache();
    
    $test1 = apcu_fetch('test1');
    $test2 = apcu_fetch('test2');
}

$test1[] = rand(1, 1000);
$test2[] = rand(1, 1000);

if($apcuAvailabe)
{
    apcu_store('test1', $test1);
    apcu_store('test2', $test2);
}

echo sprintf('current - value = %s<br/>', implode(' ,', $test1));
echo sprintf('current - value = %s<br/>', implode(' ,', $test2));

$aPCUIterator = new APCUIterator();

echo sprintf('totalCount = %s<br/>', $aPCUIterator->getTotalCount());
//echo sprintf('totalHits = %s<br/>', $aPCUIterator->getTotalHits()); // Not implemneted/available?
echo sprintf('totalSize = %s<br/>', $aPCUIterator->getTotalSize());

echo '----------------------------------<br/>';

$aPCUIterator->rewind();
echo sprintf('key = %s<br/>', $aPCUIterator->key());
echoCurrent($aPCUIterator->current());
$aPCUIterator->next();

echo '----------------------------------<br/>';

echo sprintf('key = %s<br/>', $aPCUIterator->key());
echoCurrent($aPCUIterator->current());
echo sprintf('valid = %s<br/>', $aPCUIterator->valid() ? 'true' : 'false');

function echoCurrent($current)
{
    
    echo sprintf('current - type = %s<br/>', $current['type']);
    echo sprintf('current - key = %s<br/>', $current['key']);
    echo sprintf('current - value = %s<br/>', implode(' ,', $current['value']));
    //echo sprintf('current - num_hits = %s<br/>', $current['num_hits']); // Not implemneted/available?
    echo sprintf('current - mtime = %s<br/>', date("d-m-Y H:i:s", $current['mtime']));
    echo sprintf('current - creation_time = %s<br/>', date("d-m-Y H:i:s", $current['creation_time']));
    echo sprintf('current - deletion_time = %s<br/>', date("d-m-Y H:i:s", $current['deletion_time']));
    echo sprintf('current - access_time = %s<br/>', date("d-m-Y H:i:s", $current['access_time']));
    //echo sprintf('current - ref_count = %s<br/>', $current['ref_count']); // Not implemneted/available?
    echo sprintf('current - mem_size = %s<br/>', $current['mem_size']);
    //echo sprintf('current - ttl = %s<br/>', $current['ttl']); // Not implemneted/available?
}

?>