Detailed explanation of date() function in PHP

Syntax:

string date ( string $format [, int $timestamp ] )

• format Specifies the format of the timestamp.

• timestamp specifies the timestamp. The default is the current date and time.

Among them, the most commonly used characters in format are:

• d - represents the day of the month (01 - 31)

• m - represents the month (01 - 12)

• Y - represents the year (four digits)

Example:

<?php
    echo date("Y/m/d") . "<br>";// 2021/3/22
    echo date("Y.m.d") . "<br>";// 2021.3.22
    echo date("Y-m-d");          // 2021-3-22
?>

Use time() to obtain the timestamp

                                                                                  ()In PHP, you can get a number, that is, a timestamp. This number represents the time from Greenwich Mean Time (1970-01-01) to the present.

1. So how to change this timestamp number into date format? You must use the date() function

$datetime=time(); //获取时间戳
echo date("Y-m-d H:i:s",$datetime);//将时间戳转换为要求的日期时间格式
echo date("Y年m月d日 H点i分s秒",$datetime);//其实上面的横杠（-）可以换成任意字符

2. How to convert the date into timestamp format, that is, into a string of numbers (seconds)

$str='2015-12-18 12:23:35';//设置时间变量
echo strtotime($str);//将标准的日期时间格式转为以秒为单位的时间戳数字，这里要注意，用strtotime()函数，要求被转换的时期时间为标准格式，如果用了年、月、日这种就不行了，要先转换为标准格式才行！

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