PHP - 寻找类型为String而不是Resource的fread

Question

Is there an existing function which can be implemented the same way as fread but for a string?

for example.

    while($string = str_read($huge_string, 500)) {

        echo strlen($string); // 500
    }

My current code looks like this.

    $length = 8192;

    $array  = str_split($xml, $length);

    while($string = array_shift($array)){

        if (! xml_parse($parser, $string, false))
        {
            return xml_error_string(xml_get_error_code($parser));
        }
    }
    xml_parse($parser, '', true);
    xml_parser_free($parser);

Is this the most efficient way of doing this or can it be improved to offer better performance ?

would using a $length of int_get('memory_limit'); be better as it will use less iterations ?