时间

shell操作时间

1 date        #查看或者设置系统时钟
2 cal
3 ncal
4 calendar
5 time cal
<span style="font-size:14px;color:#333333;background-color:#FFFFFF;line-height:25px;white-space:pre-wrap;">system-config-date       #图形化修改</span>

hwclock           #硬件时间 查看设置与同步

</pre></p><p></p><p>1，获取和转换日期时间（Calendar Time）</p><p>系统调用：gettimeofday(),time(),ctime(),gmtime(),localtime(),mktime(),asctime().</p><p><pre name="code" class="objc"> 19 #include <locale.h>
20 #include <time.h>
21 #include <sys/time.h>
22 #include <stdio.h>
23 #include <stdlib.h>
24 #define SECONDS_IN_TROPICAL_YEAR (365.24219*24*60*60)
25 #define S_Y SECONDS_IN_TROPICAL_YEAR
26
27 int
28 main(int argc,char *argv[])
29 {
30     time_t t;
31     struct tm *gmp, *locp;
32     struct tm gm,loc;
33     struct timeval tv;
34
35     t = time(NULL);
36     printf("Seconds since the Epoch(1 Jan 1970):%ld\t", (long)t);
37     printf("(about %6.3f years)\n", t/S_Y);
38
39     if (gettimeofday(&tv, NULL) == -1)
40       exit(EXIT_FAILURE);
41     printf("    gettimeofday() return %ld secs,%ld microsecs\n",
42                 (long) tv.tv_sec, (long) tv.tv_usec);
43
44     gmp = gmtime(&t);
45     if (gmp == NULL)
46       exit(-1);
47     gm = *gmp;    /*save local copy, since *gmp may be modified by asctime() or gmtime() */
48     printf("Broken down by gmtime():\n");
49     printf("    year:mon:mday:hour:min:sec = %d %d %d %d %d %d %d\t",
50                 gm.tm_year, gm.tm_mon, gm.tm_mday, gm.tm_hour, gm.tm_min, gm.tm_sec);
51     printf("wday:yday:isdst = %d %d %d\n",
52                 gm.tm_wday, gm.tm_yday, gm.tm_isdst);
53
54     locp = localtime(&t);
55     if (locp == NULL)
56       exit(-1);
57     loc = *locp;    /*save local copy*/
58     printf("Broken down by localtime():\n");
59     printf("    year:mon:mday:hour:min:sec = %d %d %d %d %d %d %d\t",
60                 loc.tm_year, loc.tm_mon, loc.tm_mday, loc.tm_hour, loc.tm_min, loc.tm_sec);
61     printf("wday:yday:isdst = %d %d %d\n",
62                 loc.tm_wday, loc.tm_yday, loc.tm_isdst);
63
64     printf("asctime() formats the gmtime() value as:%s", asctime(&gm));
65     printf("ctime() formats the time() value as:    %s", ctime(&t));
66
67     printf("mktime() of gmtime() value:    %ld secs\n", (long)mktime(&gm));
68     printf("mktime() of localtime() value: %ld secs\n", (long)mktime(&loc));
69     return 0;
70 }
71

#output
 Seconds since the Epoch(1 Jan 1970):1458092949    (about 46.205 years)
    gettimeofday() return 1458092949 secs,76250 microsecs
Broken down by gmtime():
    year:mon:mday:hour:min:sec = 116 2 16 1 49 9 -1437482552    wday:yday:isdst = 3 75 0
Broken down by localtime():
    year:mon:mday:hour:min:sec = 116 2 16 9 49 9 -1437482552    wday:yday:isdst = 3 75 0
asctime() formats the gmtime() value as:Wed Mar 16 01:49:09 2016
ctime() formats the time() value as:    Wed Mar 16 09:49:09 2016
mktime() of gmtime() value:    1458064149 secs
mktime() of localtime() value: 1458092949 secs

2、返回当前时间的字符串

系统调用：strftime(),currTime()

#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#define BUF_SIZE 1000

char *
currTime(const char *format)
{
static char buf[BUF_SIZE];    /* Nonreentrant*/
time_t t;
size_t s;
struct tm *tm;

t = time(NULL);
tm = localtime(&t);
if (tm == NULL)
return NULL;

s = strftime(buf, BUF_SIZE, (format != NULL) ? format : "%c", tm);

return (s == 0) ? NULL : buf;
}

3、获取和转换日历时间

系统调用：strptime（）

19 #define _XOPEN_SOURCE
20 #include <time.h>
21 #include <locale.h>
22 #include <stdlib.h>
23 #include <stdio.h>
24
25 #define SBUF_SIZE 1000
26
27 int
28 main(int argc, char *argv[])
29 {
30     struct tm tm;
31     char sbuf[SBUF_SIZE];
32     char *ofmt;
33
34     if (argc < 3 || strcmp(argv[1], "--help") == 0){
35         printf("%s input-date-time in-format [out-foramt]\n", argv[0]);
36         exit(-1);
37     }
38
39     if(setlocale(LC_ALL,"") ==NULL)
40       exit(-1);
41
42     memset(&tm, 0, sizeof(struct tm));
43     if (strptime(argv[1],argv[2], &tm) == NULL)
44       exit(-1);
45
46     tm.tm_isdst = -1;
47     printf("calendar time (seconds since Epoch): %ld\n", (long) mktime(&tm));
48
49     ofmt = (argc > 3) ? argv[3] :"%H:%M:%S %A, %d %B %Y %Z";
50     if (strftime(sbuf, SBUF_SIZE, ofmt, &tm) == 0)
51       exit(-1);
52     printf("strftime() yields: %s\n", sbuf);
53
54     return 0;
55 }

#output
$ ./a.out  "9:39:46pm 1 Feb 2016" "%I:%M:%S%p %d %b %Y"
calendar time (seconds since Epoch): 1454333986
strftime() yields: 21:39:46 星期一, 01 二月 2016 CST

$ ./a.out  "9:39:46pm 1 Feb 2016" "%I:%M:%S%p %d %b %Y" "%F %T"
calendar time (seconds since Epoch): 1454333986
strftime() yields: 2016-02-01 21:39:46

4，时区

系统调用：setlocale（），settimeofday（），adjtime（），

5、软件时钟

可配置的内核选项，常见的300赫兹可以被视频帧速度25帧每秒（PAL）和30（NTSC）整除，250赫兹（默认）

6、进程时间

系统调用：times（），clock（）。