Need an array-like structure in PHP with minimal memory usage

Question

In my PHP script I need to create an array of >600k integers. Unfortunately my webservers memory_limit is set to 32M so when initializing the array the script a

Answer 1

I took the answer by @deceze and wrapped it in a class that can handle 32-bit integers. It is append-only, but you can still use it as a simple, memory-optimized PHP Array, Queue, or Heap. AppendItem and ItemAt are both O(1), and it has no memory overhead. I added currentPosition/currentSize to avoid unnecessary fseek function calls. If you need to cap memory usage and switch to a temporary file automatically, use php://temp instead.

class MemoryOptimizedArray
{
    private $_storage;
    private $_currentPosition;
    private $_currentSize;
    const BYTES_PER_ENTRY = 4;
    function __construct()
    {
        $this->_storage = fopen('php://memory', 'rw+');
        $this->_currentPosition = 0;
        $this->_currentSize = 0;
    }
    function __destruct()
    {
        fclose($this->_storage);
    }
    function AppendItem($value)
    {
        if($this->_currentPosition != $this->_currentSize)
        {
            fseek($this->_storage, SEEK_END);
        }
        fwrite($this->_storage, pack('l', $value));
        $this->_currentSize += self::BYTES_PER_ENTRY;
        $this->_currentPosition = $this->_currentSize;
    }
    function ItemAt($index)
    {
        $itemPosition = $index * self::BYTES_PER_ENTRY;
        if($this->_currentPosition != $itemPosition)
        {
            fseek($this->_storage, $itemPosition);
        }
        $binaryData = fread($this->_storage, self::BYTES_PER_ENTRY);
        $this->_currentPosition = $itemPosition + self::BYTES_PER_ENTRY;
        $unpackedElements = unpack('l', $binaryData);
        return $unpackedElements[1];
    }
}

$arr = new MemoryOptimizedArray();
for($i = 0; $i < 3; $i++)
{
    $v = rand(-2000000000,2000000000);
    $arr->AddToEnd($v);
    print("added $v\n");
}
for($i = 0; $i < 3; $i++)
{
    print($arr->ItemAt($i)."\n");
}
for($i = 2; $i >=0; $i--)
{
    print($arr->ItemAt($i)."\n");
}