php怎样把日期转成时间戳

int strtotime ( string $time [, int $now = time() ] )

<?php
// 设置时区
date_default_timezone_set("PRC");
$time = strtotime("2018-01-18 08:08:08");
// 将指定日期转成时间戳 
// 打印当前时间  PHP_EOL 换行符，兼容不同系统
echo  $time, PHP_EOL;
// 更多实例
echo strtotime("now"), PHP_EOL;
echo strtotime("now"), PHP_EOL;
echo strtotime("10 September 2000"), PHP_EOL;
echo strtotime("+1 day"), PHP_EOL;
echo strtotime("+1 week"), PHP_EOL;
echo strtotime("+1 week 2 days 4 hours 2 seconds"), PHP_EOL;
echo strtotime("next Thursday"), PHP_EOL;
echo strtotime("last Monday"), PHP_EOL;
?>