Linux time.h头文件详解

1、相关头文件

与时间相关的头文件：time.h sys/time.h sys/times.h sys/timeb.h sys/timex.h；其中time.h是C标准库中的头文件，其余sys开头的都为Linux系统自带的头文件；

在/usr/include/time.h 定义了常用的time函数；

在/usr/include/sys目录下查看这几个文件：

sys/time.h定义了timezone结构体和Linux系统的时间函数；

sys/times.h 定义了进程使用CPU时间的结构体tms；

sys/timeb.h定义了ftime函数的返回值的结构体timeb；

sys/timex.h定义了关于时钟调整算法的结构体timex；

2、常用函数和结构体

time函数原型(time.h中)

参数：time_t (类型变量的指针)

返回值：time_t 相当于一个long类型，time用于取Epoch记年以来到现在经过的秒数(系统当前时间)，Epoch记年从1970年1月1日开始。把取到的时间存在指针指向的变量中。

localtime函数原型(在time.h中)：

struct tm *localtime(const time_t *calptr);

参数：time_t 类型变量的指针；

返回值：指向 tm 结构体的指针类型；作用是将time_t的值转换为tm结构体。然后可以打印输出。

#ifdef	_TIME_H
__BEGIN_NAMESPACE_STD
/* Used by other time functions.  */
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] */
  int tm_year;			/* Year	- 1900.  */
  int tm_wday;			/* Day of week.	[0-6] */
  int tm_yday;			/* Days in year.[0-365]	*/
  int tm_isdst;			/* DST.		[-1/0/1]*/
 
# ifdef	__USE_MISC
  long int tm_gmtoff;		/* Seconds east of UTC.  */
  const char *tm_zone;		/* Timezone abbreviation.  */
# else
  long int __tm_gmtoff;		/* Seconds east of UTC.  */
  const char *__tm_zone;	/* Timezone abbreviation.  */
# endif
};
__END_NAMESPACE_STD
#if defined __USE_XOPEN || defined __USE_POSIX
__USING_NAMESPACE_STD(tm)
#endif

ftime.h函数原型(timeb.h)

int ftime(struct timeb *tp);

参数：指向timeb结构体变量的指针；

返回值：将当前系统时间存入timeb结构体中，包括了秒和毫秒。作用是能获取当前时间精确到毫秒；

timeb结构体(sys/timeb.h)

__BEGIN_DECLS
 
/* Structure returned by the `ftime' function.  */
 
struct timeb
  {
    time_t time;		/* Seconds since epoch, as from `time'.  */
    unsigned short int millitm;	/* Additional milliseconds.  */
    short int timezone;		/* Minutes west of GMT.  */
    short int dstflag;		/* Nonzero if Daylight Savings Time used.  */
  };
 
/* Fill in TIMEBUF with information about the current time.  */
 
extern int ftime (struct timeb *__timebuf);
 
__END_DECLS

times函数原型(sys/times.h)

clock_t times(struct tms *buf);

参数：指向tms结构体变量的指针。

返回值：clock_t类型等同于long类型，用于获得进程运行时的CPU时间。

tms结构体(sys/times.h中)

__BEGIN_DECLS
 
/* Structure describing CPU time used by a process and its children.  */
struct tms
  {
    clock_t tms_utime;		/* User CPU time.  */
    clock_t tms_stime;		/* System CPU time.  */
 
    clock_t tms_cutime;		/* User CPU time of dead children.  */
    clock_t tms_cstime;		/* System CPU time of dead children.  */
  };
 
 
/* Store the CPU time used by this process and all its
   dead children (and their dead children) in BUFFER.
   Return the elapsed real time, or (clock_t) -1 for errors.
   All times are in CLK_TCKths of a second.  */
extern clock_t times (struct tms *__buffer) __THROW;
 
__END_DECLS

示例：

#include <stdio.h>
#include <time.h>
#include <sys/time.h>
#include <sys/timeb.h>
#include <sys/times.h>
#include <unistd.h>
 
int main(int argc, char* argv[])
{
    int i = 0; ///< 循环参数
    long tck = 0; ///< 获取系统时钟
    
    long l_begin_time = 0; ///< 起始时间点
    long l_end_time = 0; ///< 结束时间点
 
    time_t curr;
 
    struct tm * t_tm;
 
    struct tms t_tms;
 
    struct timeb t_tmb;
 
    tzset(); ///< 对 UNIX 操作系统的兼容性
 
    // time函数获得秒数
    time(&curr);
    printf("current time is %ld seconds\n", curr);
 
    // localtime函数转换time_t
    t_tm = localtime(&curr);
    printf("%4d-%02d-%02d %02d:%02d:%02d\n", t_tm->tm_year + 1900, t_tm->tm_mon + 1, t_tm->tm_mday, t_tm->tm_hour, t_tm->tm_min, t_tm->tm_sec);
 
    // ftime函数获得时间包括毫秒
    ftime(&t_tmb);
    t_tm = localtime(&t_tmb.time);
    printf("%4d-%02d-%02d %02d:%02d:%02d :%3d\n", t_tm->tm_year + 1900, t_tm->tm_mon + 1, t_tm->tm_mday, t_tm->tm_hour, t_tm->tm_min, t_tm->tm_sec, t_tmb.millitm);
 
    // 用times函数计算以下循环运行花费的时间
    l_begin_time = times(&t_tms);
    printf("l_begin_time = %ld\n", l_begin_time);
    while (1)
    {
        i = i + 1;
        if (i == 0)
        {
            break;
        }
    }
    l_end_time = times(&t_tms);
    printf("l_end_time = %ld\n", l_end_time);
    printf("used CPU time: %ld\n", l_end_time - l_begin_time);
    tck = sysconf(_SC_CLK_TCK); ///< 获取系统时钟(1秒里有多少个)
    printf("transform minutes: %f\n", ((l_end_time - l_begin_time) / (double)tck));
 
    return 0;
}

执行结果：