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)
#endifftime.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_DECLStimes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：
