time函数

time函数

• time

#include<time.h>

time_t time(time_t *t);

time() returns the time as the number of secs since 1970-01-01 00:00:00 +0000(UTC)

假如参数t不是NULL，返回值（秒数）(日历时间）也存储在t中。

失败返回-1.

• ctime

#include <time.h>

char *ctime(const time_t *time);

将秒数转化为具体日期（ASCII），长度固定26字节。

the time is 1449579811

the time ascii is Tue Dec  8 21:03:31 2015

等价：asctime(localtime(t));

• broken-down time

Broken-down time is stored in the structure tm whichi is deiined in time.h as follows:

struct tm {

    int tm_sec;

    int tm_min;

    int tm_hour;

    int tm_mday;

    int tm_mon;

    int tm_year;

    int tm_wday;

    int tm_yday;

    int tm_isdst;

};

tm_year指的是自1900年以来的年数。

• asctime

char *asctime(const struct tm *tm);

将分离时间装换为字符串时间。

• localtime

struct tm *localtime(const time_t *timep);

将秒数装换为分离时间。

• gmtime

struct tm *gmtime(const time_t *timep);

• mktime

time_t mktime(struct tm *tm);

将分离时间转换为秒数。

• difftime

double difftime(time_t time1, time_t time0);

The difftime() function returns the number of seconds elapsed between time time1 and time time0, represented as a double. Each of the times is specified in calendar time, which means its value is a measurement (in seconds) relative to the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

• clock

clock_t clock(void);

DESCRIPTION

   The  clock()  function returns an approximation of processor time used

   by the program.

RETURN VALUE

   The value returned is the CPU time used so far as a  clock_t;  to  get

   the  number of seconds used, divide by CLOCKS_PER_SEC.  If the proces‐

   sor time used is not available or its value cannot be represented, the

   function returns the value (clock_t) -1.

time函数

原文：http://www.cnblogs.com/embedded-linux/p/5031179.html