天地四方曰宇，往古来今曰宙
时间是世界的重要组成部分，不论花开花落，还是云卷云舒都有它的影子。
但它源起何处？又将去向何方？没人知道答案，也不需要答案，我们需要的只是一个相对的起点来标识时间，现今世界普遍采用公元纪年法来表示。
公元纪年法以耶稣诞生日记为公元1年（没有公元0年），中国处于汉平帝刘衎（不会读。。。）登基第二年即元始元年。
关于时间的另一个概念是unix时间戳，是从1970年1月1日开始所经过的秒数，不考虑闰秒，什么是闰秒参考这里。
下面就来说说php中时间的处理方法，以获取当前时间为例
<?php
date_default_timezone_set('Asia/Shanghai');
echo "now is ".date("Y-m-d H:i:s",time())."\n";
echo "now is ".date("Y-m-d H:i:s",strtotime("now"))."\n";
$date = new DateTime();
echo "now is ".$date->format("Y-m-d H:i:s")."\n";
?>
时区设置
date_default_timezone_set用于设置时区，优先级别高于php.ini中设置的date.timezone属性，可设置的时区列表见这里，与之对应的是date_default_timezone_get获取由set函数设置的时区。
<?php
date_default_timezone_set('Asia/Shanghai');
$date_set = date_default_timezone_get();
//如果与配置文件中的时区设置相同则设置为美国时区
if($date_set == ini_get("date.timezone")){
date_default_timezone_set('America/Los_Angeles');
}
echo date("Y-m-d H:i:s")."\n";
?>
获取UNIX时间戳
常用的方法有三种：time(),microtime(),strotime("now")
<?php
error_reporting(E_ALL ^E_STRICT);
echo "time is ".time()."\n";
echo "strotime is ".strtotime("now")."\n";
echo "mktime is ".mktime()."\n";
echo "microtime is ".microtime()."\n";
//参数设置为true返回浮点数表示的时间戳
echo "in float microtime is ".microtime(true)."\n";
?>
mktime
mktime函数的参数全是关键字参数，关键字参数大家懂的可以从右到左省略，格式为时，分，秒，月，日，年
<?php
//年默认2014
echo "mktime(10,10,10,10,12) is ".date("Y-m-d H:i:s",mktime(10,10,10,10,12))."\n";
//这种写法会将2014当作月数，年还是默认的2014年
echo "mktime(10,10,10,10,2014) is ".date("Y-m-d H:i:s",mktime(10,10,10,10,2014))."\n";
echo "mktime(10,10,10,10,32,2014) is ".date("Y-m-d H:i:s",mktime(10,10,10,10,32,2014))."\n";
?>
出现了一些很奇妙的事情，2014年2014月变成了2020年4月，2014年10月32号变成了11月1号，看，mktime自动计算了相差部分。乍看之下感觉很神奇，细想下来又在情理之中，毕竟日期的相互转换是通过unix时间戳进行的，我们可以通过mktime的实现源码管中窥豹一下。
该函数源码位于ext/date/php_date.c 在1500行实现，篇幅所限只贴部分代码，兴趣的朋友可以下下来自己看，地址在这里.
PHPAPI void php_mktime(INTERNAL_FUNCTION_PARAMETERS, int gmt)
{
zend_long hou = 0, min = 0, sec = 0, mon = 0, day = 0, yea = 0, dst = -1;
timelib_time *now;
timelib_tzinfo *tzi = NULL;
zend_long ts, adjust_seconds = 0;
int error; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "|lllllll", &hou, &min, &sec, &mon, &day, &yea, &dst) == FAILURE) {
RETURN_FALSE;
}
/* Initialize structure with current time */
now = timelib_time_ctor();
if (gmt) {
timelib_unixtime2gmt(now, (timelib_sll) time(NULL));
} else {
tzi = get_timezone_info(TSRMLS_C);
now->tz_info = tzi;
now->zone_type = TIMELIB_ZONETYPE_ID;
timelib_unixtime2local(now, (timelib_sll) time(NULL));
}
/* Fill in the new data */
switch (ZEND_NUM_ARGS()) {
case 7:
/* break intentionally missing */
case 6:
if (yea >= 0 && yea < 70) {
yea += 2000;
} else if (yea >= 70 && yea <= 100) {
yea += 1900;
}
now->y = yea;
/* break intentionally missing again */
case 5:
now->d = day;
/* break missing intentionally here too */
case 4:
now->m = mon;
/* and here */
case 3:
now->s = sec;
/* yup, this break isn't here on purpose too */
case 2:
now->i = min;
/* last intentionally missing break */
case 1:
now->h = hou;
break;
default:
php_error_docref(NULL TSRMLS_CC, E_STRICT, "You should be using the time() function instead");
}
/* Update the timestamp */
if (gmt) {
timelib_update_ts(now, NULL);
} else {
timelib_update_ts(now, tzi);
}
/* Support for the deprecated is_dst parameter */
if (dst != -1) {
php_error_docref(NULL TSRMLS_CC, E_DEPRECATED, "The is_dst parameter is deprecated");
if (gmt) {
/* GMT never uses DST */
if (dst == 1) {
adjust_seconds = -3600;
}
} else {
/* Figure out is_dst for current TS */
timelib_time_offset *tmp_offset;
tmp_offset = timelib_get_time_zone_info(now->sse, tzi);
if (dst == 1 && tmp_offset->is_dst == 0) {
adjust_seconds = -3600;
}
if (dst == 0 && tmp_offset->is_dst == 1) {
adjust_seconds = +3600;
}
timelib_time_offset_dtor(tmp_offset);
}
}
/* Clean up and return */
ts = timelib_date_to_int(now, &error);
ts += adjust_seconds;
timelib_time_dtor(now); if (error) {
RETURN_FALSE;
} else {
RETURN_LONG(ts);
}
}
阅读这段代码需知道一个重要的结构体timelib_time，在ext/date/lib/timelib_structs.h中声明
typedef struct timelib_time {
timelib_sll y, m, d; /* Year, Month, Day */
timelib_sll h, i, s; /* Hour, mInute, Second */
double f; /* Fraction */
int z; /* GMT offset in minutes */
char *tz_abbr; /* Timezone abbreviation (display only) */
timelib_tzinfo *tz_info; /* Timezone structure */
signed int dst; /* Flag if we were parsing a DST zone */
timelib_rel_time relative;
timelib_sll sse; /* Seconds since epoch */
unsigned int have_time, have_date, have_zone, have_relative, have_weeknr_day;
unsigned int sse_uptodate; /* !0 if the sse member is up to date with the date/time members */
unsigned int tim_uptodate; /* !0 if the date/time members are up to date with the sse member */
unsigned int is_localtime; /* 1 if the current struct represents localtime, 0 if it is in GMT */
unsigned int zone_type; /* 1 time offset,
* 3 TimeZone identifier,
* 2 TimeZone abbreviation */
} timelib_time;
现在来看看mktime,56行的timelib_update_ts函数位于ext/date/lib/tm2unixtime.c文件中，其作用是根据now中的日期信息计算相应的秒数并存入now->sse，来看看
void timelib_update_ts(timelib_time* time, timelib_tzinfo* tzi)
{
timelib_sll res = ; do_adjust_special_early(time);
do_adjust_relative(time);
do_adjust_special(time);
res += do_years(time->y);
res += do_months(time->m, time->y);
res += do_days(time->d);
res += do_time(time->h, time->i, time->s);
time->sse = res; res += do_adjust_timezone(time, tzi);
time->sse = res; time->sse_uptodate = ;
time->have_relative = time->relative.have_weekday_relative = time->relative.have_special_relative = ;
}
8-11行计算相应时间类型的秒数，到这里已可了解mktime自动增减日期的原理，让我们看看do_days是如何实现的。day-1应该不难理解，mktime前面需要传入小时分钟等参数，在处理具体的某一天时默认为当天的0点0分0秒，所以要比实际的天数少一天。do_months,do_years等机制都相同，不再细述。
static timelib_sll do_days(timelib_ull day)
{
return ((day - ) * SECS_PER_DAY);
}
当日期处理完成，我们回到php_date.c，在80行处通过timelib_date_to_int函数将now->sse返回，该函数位于ext/date/lib/timelib.c，具体的代码就不贴了。
strtotime
聊完了mktime，再来看看strtotime，同样先来几个例子
<?php
echo "strtotime('+1 day',strtotime('2014/10/19')) is ".date("Y-m-d",strtotime("+1 day",strtotime("2014/10/19")))."\n";
echo "strtotime('-30 day') is ".date("Y-m-d",strtotime("-30 day"))."\n";
echo "strtotime('+1 week') is ".date("Y-m-d",strtotime("+1 week"))."\n";
echo "strtotime('last Monday) is ".date("Y-m-d",strtotime("last Monday"))."\n";
?>
strtotime相较mktime要复杂很多，在于其对英文文本的解析过程，这里用到了词法解析工具re2c，原始文件位于ext/date/lib/parse_date.re,同目录下还有个parse_date.c是编译后的文件,parse_date.c太大，我们分析parse_date.re就可以了，以strtotime("+1 day")为例，下面是php_date.c中的实现代码
PHP_FUNCTION(strtotime)
{
char *times, *initial_ts;
size_t time_len;
int error1, error2;
struct timelib_error_container *error;
zend_long preset_ts = , ts; timelib_time *t, *now;
timelib_tzinfo *tzi; tzi = get_timezone_info(TSRMLS_C); if (zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET, ZEND_NUM_ARGS() TSRMLS_CC, "sl", ×, &time_len, &preset_ts) != FAILURE) {
/* We have an initial timestamp */
now = timelib_time_ctor(); initial_ts = emalloc();
snprintf(initial_ts, , "@" ZEND_LONG_FMT " UTC", preset_ts);
t = timelib_strtotime(initial_ts, strlen(initial_ts), NULL, DATE_TIMEZONEDB, php_date_parse_tzfile_wrapper); /* we ignore the error here, as this should never fail */
timelib_update_ts(t, tzi);
now->tz_info = tzi;
now->zone_type = TIMELIB_ZONETYPE_ID;
timelib_unixtime2local(now, t->sse);
timelib_time_dtor(t);
efree(initial_ts);
} else if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s|l", ×, &time_len, &preset_ts) != FAILURE) {
/* We have no initial timestamp */
now = timelib_time_ctor();
now->tz_info = tzi;
now->zone_type = TIMELIB_ZONETYPE_ID;
timelib_unixtime2local(now, (timelib_sll) time(NULL));
} else {
RETURN_FALSE;
} if (!time_len) {
timelib_time_dtor(now);
RETURN_FALSE;
} t = timelib_strtotime(times, time_len, &error, DATE_TIMEZONEDB, php_date_parse_tzfile_wrapper);
error1 = error->error_count;
timelib_error_container_dtor(error);
timelib_fill_holes(t, now, TIMELIB_NO_CLONE);
timelib_update_ts(t, tzi);
ts = timelib_date_to_int(t, &error2); timelib_time_dtor(now);
timelib_time_dtor(t); if (error1 || error2) {
RETURN_FALSE;
} else {
RETURN_LONG(ts);
}
}
if用来解析参数，分为有第二个参数和没有第二个参数的情况，这里略过不提，主要关注timelib_strtotime函数，它在parse_date.re中定义，返回解析后的timelib_time结构体。而timelib_strtotime又会调用parse_date.re中的scan方法来解析字符串，这里有几个重要的正则表达式
reltextnumber = 'first'|'second'|'third'|'fourth'|'fifth'|'sixth'|'seventh'|'eight'|'eighth'|'ninth'|'tenth'|'eleventh'|'twelfth';
reltexttext = 'next'|'last'|'previous'|'this';
reltextunit = (('sec'|'second'|'min'|'minute'|'hour'|'day'|'fortnight'|'forthnight'|'month'|'year') 's'?) | 'weeks' | daytext; relnumber = ([+-]*[ \t]*[-]+);
relative = relnumber space? (reltextunit | 'week' );
relativetext = (reltextnumber|reltexttext) space reltextunit;
relativetextweek = reltexttext space 'week';
"+1 day"会被解析为relative,并进行relative的相关操作
relative
{
timelib_ull i;
DEBUG_OUTPUT("relative");
TIMELIB_INIT;
TIMELIB_HAVE_RELATIVE(); while(*ptr) {
i = timelib_get_unsigned_nr((char **) &ptr, );
timelib_eat_spaces((char **) &ptr);
timelib_set_relative((char **) &ptr, i, , s);
}
TIMELIB_DEINIT;
return TIMELIB_RELATIVE;
}
timelib_get_unsigned_nr 用来判断是"+"还是"-"，参数24用来指定最大的字符串长度，然后调用timelib_get_nr获取后面的具体数字，最后调用timelib_set_relative设置timelib_time 结构体中relative.d=1。
static timelib_ull timelib_get_unsigned_nr(char **ptr, int max_length)
{
timelib_ull dir = ; while (((**ptr < '') || (**ptr > '')) && (**ptr != '+') && (**ptr != '-')) {
if (**ptr == '\0') {
return TIMELIB_UNSET;
}
++*ptr;
} while (**ptr == '+' || **ptr == '-')
{
if (**ptr == '-') {
dir *= -;
}
++*ptr;
}
return dir * timelib_get_nr(ptr, max_length);
}
static void timelib_set_relative(char **ptr, timelib_sll amount, int behavior, Scanner *s)
{
const timelib_relunit* relunit; if (!(relunit = timelib_lookup_relunit(ptr))) {
return;
} switch (relunit->unit) {
case TIMELIB_SECOND: s->time->relative.s += amount * relunit->multiplier; break;
case TIMELIB_MINUTE: s->time->relative.i += amount * relunit->multiplier; break;
case TIMELIB_HOUR: s->time->relative.h += amount * relunit->multiplier; break;
case TIMELIB_DAY: s->time->relative.d += amount * relunit->multiplier; break;
case TIMELIB_MONTH: s->time->relative.m += amount * relunit->multiplier; break;
case TIMELIB_YEAR: s->time->relative.y += amount * relunit->multiplier; break; case TIMELIB_WEEKDAY:
TIMELIB_HAVE_WEEKDAY_RELATIVE();
TIMELIB_UNHAVE_TIME();
s->time->relative.d += (amount > ? amount - : amount) * ;
s->time->relative.weekday = relunit->multiplier;
s->time->relative.weekday_behavior = behavior;
break; case TIMELIB_SPECIAL:
TIMELIB_HAVE_SPECIAL_RELATIVE();
TIMELIB_UNHAVE_TIME();
s->time->relative.special.type = relunit->multiplier;
s->time->relative.special.amount = amount;
}
}
timelib_set_relative
随后就和mktime一样调用相关处理函数转换为时间戳，有一点需要注意，timelib_set_relative的实现方式是直接在日期或月份上操作，下面这样的代码会出现问题
echo date("Y-m-d",strtotime("-1 month",strtotime("2014/03/31")))."\n";
输出结果为2014-03-03，按照上述流程，2014/03/31会转为2014/02/31处理，等价于mktime(00,00,00,2,31,2014),mktime的处理方式上文已经说过了:P
写一些常用的方法
知道了原理，用起来就很方便了。下面是使用频率较高的时间处理方法，例如获取前几周，前几天，取得本周第一天和最后一天的时间等等，不定期更新,github地址。
<?php
/**
* process date
* @author huntstack
* @time 2014-10-18
*/
class Process_Date{
private $date;
private $M,$D,$Y;
/**
* set the date for next operator
* @parameter date:time string or timestamp
*/
function __construct($date=""){
if($date == "" || empty($date)){
$this->date = strtotime("now");
}else if(gettype($date) == "string"){
$this->date = strtotime($date);
}else if(gettype($date) == "integer"){
$this->date = $date;
}else{
throw new Exception("paramter must be timestamp or date string or empty for current time");
}
$this->set_varibales();
}
public function set_date($date){
$this->date = strtotime($date);
$this->set_varibales();
}
private function set_varibales(){
$this->M = date("m",$this->date);
$this->D = date("d",$this->date);
$this->Y = date("Y",$this->date);
}
/**
* get the specified weeks
* @parameter $i:numbers of week
* @parameter $flag:0->last,1->next
*/
public function get_week($i=0,$flag=1){
if($flag == 0) return date("YW",strtotime("-$i week",$this->date));
else if($flag == 1) return date("YW",strtotime("+$i week",$this->date));
}
/**
* get the specified months
* @parameter $i:numbers of month
* @parameter $flag:0->last,1->next
*/
public function get_month($i=0,$flag=1){
if($flag == 0) return date("Y-m",mktime(0,0,0, $this->M-$i, 1, $this->Y));
else if($flag == 1) return date("Y-m",mktime(0,0,0, $this->M+$i, 1, $this->Y));
}
/**
* get the specified days
* @parameter $i:numbers of day
* @parameter $flag:0->last,1->next
*/
public function get_day($i=0,$flag=1){
if($flag == 0) return date("Y-m-d",mktime(0,0,0, $this->M, $this->D-$i, $this->Y));
else if($flag == 1) return date("Y-m-d",mktime(0,0,0, $this->M, $this->D+$i, $this->Y));
}
/**
* get the last $count days
* @parameter count:number
*/
public function get_last_days($count){
$return = array();
for($i=1;$i<=$count;$i++){
array_push($return, $this->get_day($i,0));
}
return $return;
}
/**
* get the next $count days
* @parameter count:number
*/
public function get_next_days($count){
$return = array();
for($i=1;$i<=$count;$i++){
array_push($return, $this->get_day($i,1));
}
return $return;
}
/**
* get the last $count weeks
* @parameter count:number
*/
public function get_last_weeks($count){
$return = array();
for($i=1;$i<=$count;$i++){
array_push($return, $this->get_week($i,0));
}
return $return;
}
/**
* get the next $count weeks
* @parameter count:number
*/
public function get_next_weeks($count){
$return = array();
for($i=1;$i<=$count;$i++){
array_push($return, $this->get_week($i,1));
}
return $return;
}
/**
* get the last $count months
* @parameter count:number
*/
public function get_last_month($count){
$return = array();
for($i=1;$i<=$count;$i++){
array_push($return, $this->get_month($i,0));
}
return $return;
}
/**
* get the next $count months
* @parameter count:number
*/
public function get_next_month($count){
$return = array();
for($i=1;$i<=$count;$i++){
array_push($return, $this->get_month($i,1));
}
return $return;
}
/**
* get the first day and the last day of a week
*/
public function get_week_begin_end(){
$return["begin"] = mktime(0,0,0, $this->M, $this->D-date("w",$this->date)+1, $this->Y);
$return["end"] = mktime(23,59,59, $this->M, $this->D-date("w",$this->date)+7, $this->Y);
return $return;
}
/**
* get the first day and the last day of a month
*/
public function get_month_begin_end(){
$return["begin"] = strtotime("first day of",$this->date);
$return["end"] = strtotime("last day of",$this->date);
return $return;
}
}
?>
参考资料：
1.http://php.net/manual/zh/book.datetime.php
2.http://www.phppan.com/2011/06/php-strtotime/