Share a php function that randomly generates strings

/**
 * 随机字符
 * @param number $length 长度
 * @param string $type 类型
 * @param number $convert 转换大小写
 * @return string
 */
function random($length=6, $type='string', $convert=0){
 
    $config = array(
        'number'=>'1234567890',
        'letter'=>'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',
        'string'=>'abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789',
        'all'=>'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'
    );
     
    if(!isset($config[$type])) $type = 'string';
    $string = $config[$type];
     
    $code = '';
    $strlen = strlen($string) -1;
    for($i = 0; $i < $length; $i++){
        $code .= $string{mt_rand(0, $strlen)};
    }
    if(!empty($convert)){
        $code = ($convert > 0)? strtoupper($code) : strtolower($code);
    }
    return $code;
}