PHP 6位随机数生成

# 卡密生成器
function generateRandomString($huodong)
{
    $characters = 'ABCDEFGHJKLMNPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < 1; $i++) {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    }
    /* 生成的字符串 */
    # X123456
    $number = $randomString . str_pad(mt_rand(0, 999999), 6, '0', STR_PAD_LEFT);
    // 纯数字
    // str_pad(mt_rand(0, 999999), 6, '0', STR_PAD_LEFT)
    return number ;
}