PHP time and date operation practice

Commonly used time functions:
(); //Get the total number of seconds from 1970/1/1 00:00:00 to the present

<?echo time();?>
(); //Set time

<?echo date("U",mktime(0,0,0,1,20,2011));//Output the total number of seconds from 0:00:00 on January 1, 1970 to 0:00 on January 20, 2011 //mktime parameters: mktime(hour, minute, second, month, day, year);//Constantly used in combination with date("U",mktime(hour, minute, second, month, day, year));?>
(); //Retrieve detailed information on time

<?echo date("Y-m-d H:i:s");//Output the first year of Xi - month-day hour: minute: seconds;// Please refer to the table below for filling parameters;?>

Representative string	illustrate	example	Output
Year:
Y	First year of Xi (4)	<?=date("Y")?>	2011
y	First year of Xi (2)	<?=date("y")?>	11
moon:
m	In the month, less than two people make up for zero (01~12)	<?=date("m")?>	01
n	In the month, less than two people will not make up for zero (1~12)	<?=date("n")?>	1
t	How many days will be this month (1~31)	<?=date("t")?>	31
M	English month name (abbreviation)	<?=date("M")?>	Jan
F	English month name (full name)	<?=date("F")?>	January
day:
d	Date, less than two digits to make up for zeros (01~31)	<?=date("d")?>	01
j	Date, less than two digits will not be supplemented (01~31)	<?=date("j")?>	1
Week:
w	Digital week, (0~6 represents one to day)	<?=date("w")?>	0
D	Week name (abbreviation)	<?=date("D")?>	Sun
l	Week name (full name)	<?=date("l")?>	Sunday
hour:
H	24:00 hours, less than two digits can make up for zero (00~23)	<?=date("H")?>	07
G	24:00 hours, less than two people will not make up for zero (0~23)	<?=date("G")?>	7
h	12:00 hours, less than two digits can make up for zero (01~12)	<?=date("h")?>	07
g	12 o'clock time, no zero will be added if less than two persons (1~12)	<?=date("g")?>	7
point:
i	Minutes, less than two digits make up for zero (00~59)	<?=date("i")?>	40
Second:
s	In seconds, less than two digits can be compensated for zero (00~59)	<?=date("s")?>	45
S	In seconds, less than two digits to make up for zeros (00~59) plus English order	<?=date("S")?>	45th
Morning and afternoon:
A	Caps AM/PM	<?=date("A")?>	AM
a	Lowercase am/pm	<?=date("a")?>	am
other:
U	1970/1/1 00:00:00 Total seconds to the specified day	<?=date("U")?>	1156780800
z	What day of the year (0~365)	<?=date("z")?>	255

*Red base represents commonly used parameters

Some common usages:
1. Obtain the total number of seconds from January 1, 1970 to today:

2. Get the total number of seconds from today to the first and next 7 days: