Linux C語言時間相關(guān)知識總結(jié)

大家好，我是LinuxZn。

實際開發(fā)中，經(jīng)常要獲取各種時間。下面匯總幾個常用的時間接口：

1、clock_gettime

?

#include?

/**
?*?@brief?根據(jù)系統(tǒng)時鐘的類型，獲取當(dāng)前時間
?*
?*?Detailed?function?description
?*
?*?@param[in]?__clock_id:?系統(tǒng)時鐘的類型。常用取值：
??????????????????????????-?CLOCK_REALTIME:?從1970年1月1日到目前的時間
??????????????????????????-?CLOCK_MONOTONIC:?系統(tǒng)啟動時間
??????????????????????????-?CLOCK_PROCESS_CPUTIME_ID:?本進程運行時間
??????????????????????????-?CLOCK_THREAD_CPUTIME_ID:?本線程運行的時間
?*?@param[out]?__tp:?存放當(dāng)前的時間。
?*
?*?@return?成功則返回0，失敗則返回-1
?*/
int?clock_gettime?(clockid_t?__clock_id,?struct?timespec?*__tp);

?

timespec結(jié)構(gòu)體：

?

struct?timespec
{
??__time_t?tv_sec;??/*?Seconds.?秒?*/
??__syscall_slong_t?tv_nsec;?/*?Nanoseconds.??納秒*/
};

?

例子：

?

#include?
#include?
#include?

long?long?get_clock_sys_time_ns(void)
{
????struct?timespec?tp;
????long?long?time_ns?=?0;

????clock_gettime(CLOCK_MONOTONIC,?&tp);
????time_ns?=?(long?long)tp.tv_sec?*?1000000000?+?tp.tv_nsec;

????return?time_ns;
}

int?main(void)
{
????struct?timespec?tp;

????///

	?

	編譯、運行：

	

	2、gettimeofday

	?
#include?

/**
?*?@brief?獲取當(dāng)前時間（從1970年1月1日到目前的時間）
?*
?*?Detailed?function?description
?*
?*?@param[out]?tv:?當(dāng)前UTC時間
?*?@param[out]?tz:?當(dāng)前時區(qū)信息
?*
?*?@return?成功則返回0，失敗則返回-1
?*/
int?gettimeofday(struct?timeval?*tv,?struct?timezone?*tz);


	?

	timeval結(jié)構(gòu)體：

	?
struct?timeval
{
??__time_t?tv_sec;??/*?Seconds.??秒*/
??__suseconds_t?tv_usec;?/*?Microseconds.??微秒*/
};


	?

	timezone結(jié)構(gòu)體：

	?
struct?timezone
??{
????int?tz_minuteswest;??/*?Minutes?west?of?GMT.?和Greenwich時間差了多少分鐘?*/
????int?tz_dsttime;??/*?Nonzero?if?DST?is?ever?in?effect.?日光節(jié)約時間的狀態(tài)??*/
??};



	?

	例子：

	?
#include?
#include?
#include?

long?long?get_sys_time_ms(void)
{
????long?long?time_ms?=?0;
????struct?timeval?tv;

????gettimeofday(&tv,?NULL);
????time_ms?=?((long?long)tv.tv_sec*1000000?+?tv.tv_usec)?/?1000;

????return?time_ms;
}

int?main(void)
{
????///

	?

	編譯、運行：

	

	3、time

	?
#include?

/**
?*?@brief?獲取1970-01-01?0000?+0000至今的秒數(shù)（UTC）
?*
?*?Detailed?function?description
?*
?*?@param[out]?tloc:?返回的秒存儲指針
?*
?*?@return?成功則返回秒數(shù)，失敗則返回-1，錯誤原因存在errno中。
?*/
time_t?time(time_t?*tloc);


	?

	time_t的類型：

	?
typedef?long?time_t;


	?

	例子：

	?
#include?
#include?

time_t?get_utc_time(void)
{
????return?time(NULL);
}

int?main(int?argc,?char?**argv)
{
????time_t?utc_time?=?get_utc_time();
????printf("utc_time?=?%ld?s
",?utc_time);

????return?0;
}


	?

	編譯、運行：

	

	4、localtime

	?
#include?

/**
?*?@brief?將time_t類型的時間轉(zhuǎn)換為struct?tm類型的時間
?*
?*?Detailed?function?description
?*
?*?@param[in]?timep:?當(dāng)前UTC秒數(shù)
?*
?*?@return?返回當(dāng)?shù)貢r間
?*/
struct?tm?*localtime(const?time_t?*timep);


	?

	tm結(jié)構(gòu)體：

	?
struct?tm
{
??int?tm_sec;???/*?Seconds.?[0-60]?(1?leap?second)?*/
??int?tm_min;???/*?Minutes.?[0-59]?*/
??int?tm_hour;???/*?Hours.?[0-23]?*/
??int?tm_mday;???/*?Day.??[1-31]?*/
??int?tm_mon;???/*?Month.?[0-11]?注意：0代表1月，以此類推*/
??int?tm_year;???/*?Year?-?1900.??該值為實際年份減去1900*/
??int?tm_wday;???/*?Day?of?week.?[0-6]?注意：0代表星期一，以此類推*/
??int?tm_yday;???/*?Days?in?year.[0-365]?從每年的1月1日開始的天數(shù)，其中0代表1月1日，以此類推*/
??int?tm_isdst;???/*?DST.??[-1/0/1]?夏玲時標識符*/
};


	?

	例子：

	?
#include?
#include?

time_t?get_utc_time(void)
{
????return?time(NULL);
}

int?main(int?argc,?char?**argv)
{
????time_t?utc_time?=?get_utc_time();
????printf("utc_time?=?%ld?s
",?utc_time);

????struct?tm?*local_tm?=?localtime(&utc_time);?
????printf("local?time?=?%.4d-%.2d-%.2d?%.2d:%.2d:%.2d
",?local_tm->tm_year?+?1900,
???????????????????????????????????????????????????????????local_tm->tm_mon?+?1,
???????????????????????????????????????????????????????????local_tm->tm_mday,
???????????????????????????????????????????????????????????local_tm->tm_hour,
???????????????????????????????????????????????????????????local_tm->tm_min,
???????????????????????????????????????????????????????????local_tm->tm_sec);

????return?0;
}


	?

	編譯、運行：

	

	5、localtime_r

	?
#include?

/**
?*?@brief?將time_t類型的時間轉(zhuǎn)換為struct?tm類型的時間
?*
?*?Detailed?function?description
?*
?*?@param[in]?timep:?當(dāng)前UTC秒數(shù)
?*?@param[out]?timep:?當(dāng)?shù)貢r間
?*
?*?@return?返回當(dāng)?shù)貢r間
?*/
struct?tm?*localtime_r(const?time_t?*timep,?struct?tm?*result);


	?

	localtime不是一個線程安全的函數(shù)，關(guān)于線程安全的知識點，看閱讀往期文章：如何理解線程安全？。

	對于實時性要求較高的系統(tǒng)，多個線程同時調(diào)用localtime，可能會造成數(shù)據(jù)被覆蓋。我們項目中之前是用localtime來獲取系統(tǒng)時間、日期。并使用這個數(shù)據(jù)去做邏輯，數(shù)據(jù)異常導(dǎo)致了邏輯異常。

	后面使用localtime_r來替代，問題解決。

	例子：

	?
#include?
#include?

time_t?get_utc_time(void)
{
????return?time(NULL);
}

int?main(int?argc,?char?**argv)
{
????time_t?utc_time?=?get_utc_time();
????printf("utc_time?=?%ld?s
",?utc_time);
????struct?tm?result;
????struct?tm?*local_tm?=?localtime_r(&utc_time,?&result);?
????printf("local?time?=?%.4d-%.2d-%.2d?%.2d:%.2d:%.2d
",?local_tm->tm_year?+?1900,
???????????????????????????????????????????????????????????local_tm->tm_mon?+?1,
???????????????????????????????????????????????????????????local_tm->tm_mday,
???????????????????????????????????????????????????????????local_tm->tm_hour,
???????????????????????????????????????????????????????????local_tm->tm_min,
???????????????????????????????????????????????????????????local_tm->tm_sec);

????printf("result?time?=?%.4d-%.2d-%.2d?%.2d:%.2d:%.2d
",?result.tm_year?+?1900,
????????????????????????????????????????????????????????????result.tm_mon?+?1,
????????????????????????????????????????????????????????????result.tm_mday,
????????????????????????????????????????????????????????????result.tm_hour,
????????????????????????????????????????????????????????????result.tm_min,
????????????????????????????????????????????????????????????result.tm_sec);

????return?0;
}


	?

	編譯、運行：

	

	6、gmtime

	?
#include?

/**
?*?@brief?返回tm結(jié)構(gòu)的GMT時間（UTC時間）
?*
?*?Detailed?function?description
?*
?*?@param[in]?timep:?當(dāng)前UTC秒數(shù)
?*
?*?@return?返回當(dāng)?shù)貢r間
?*/
struct?tm?*gmtime(const?time_t?*timep);


	?

	例子：

	?
#include?
#include?

time_t?get_utc_time(void)
{
????return?time(NULL);
}

int?main(int?argc,?char?**argv)
{
????time_t?utc_time?=?get_utc_time();
????printf("utc_time?=?%ld?s
",?utc_time);

????struct?tm?*gmt_tm?=?gmtime(&utc_time);?
????printf("gmt?time?=?%.4d-%.2d-%.2d?%.2d:%.2d:%.2d
",?gmt_tm->tm_year?+?1900,
?????????????????????????????????????????????????????????gmt_tm->tm_mon?+?1,
?????????????????????????????????????????????????????????gmt_tm->tm_mday,
?????????????????????????????????????????????????????????gmt_tm->tm_hour,
?????????????????????????????????????????????????????????gmt_tm->tm_min,
?????????????????????????????????????????????????????????gmt_tm->tm_sec);

????return?0;
}


	?

	編譯、運行：

	

	localtime和gmtime的區(qū)別？

	localtime和gmtime都是C語言中的函數(shù)，用于將time_t類型的時間轉(zhuǎn)換為struct tm類型的時間。它們的區(qū)別在于，gmtime將time_t轉(zhuǎn)換為UTC時間，即世界標準時間，而localtime將time_t轉(zhuǎn)換為本地時間。

	例子：使用gmtime與localtime接口返回的小時數(shù)來計算當(dāng)?shù)貢r區(qū)

	?
#include?
#include?

time_t?get_utc_time(void)
{
????return?time(NULL);
}

int?main(int?argc,?char?**argv)
{
????time_t?utc_time?=?get_utc_time();
????printf("utc_time?=?%ld?s
",?utc_time);

????struct?tm?*gmt_tm?=?gmtime(&utc_time);?
????printf("gmt?time?=?%.4d-%.2d-%.2d?%.2d:%.2d:%.2d
",?gmt_tm->tm_year?+?1900,
?????????????????????????????????????????????????????????gmt_tm->tm_mon?+?1,
?????????????????????????????????????????????????????????gmt_tm->tm_mday,
?????????????????????????????????????????????????????????gmt_tm->tm_hour,
?????????????????????????????????????????????????????????gmt_tm->tm_min,
?????????????????????????????????????????????????????????gmt_tm->tm_sec);
????int?gmt_hour?=?gmt_tm->tm_hour;

????struct?tm?*local_tm?=?localtime(&utc_time);?
????printf("local?time?=?%.4d-%.2d-%.2d?%.2d:%.2d:%.2d
",?local_tm->tm_year?+?1900,
???????????????????????????????????????????????????????????local_tm->tm_mon?+?1,
???????????????????????????????????????????????????????????local_tm->tm_mday,
???????????????????????????????????????????????????????????local_tm->tm_hour,
???????????????????????????????????????????????????????????local_tm->tm_min,
???????????????????????????????????????????????????????????local_tm->tm_sec);
????int?local_hour?=?local_tm->tm_hour;


????int?local_time_zone?=?local_hour?-?gmt_hour;
????if?(local_time_zone??12)?
????{
????????local_time_zone?-=?24;
????}else{}

????printf("local_time_zone?=?%d
",?local_time_zone);

????return?0;
}


	?

	編譯、運行：

	

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	審核編輯：湯梓紅