Linux/Unix系统编程手册-笔记9.时间

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#include <locale.h>
#include <time.h>
#include <sys/time.h>
#include "tlpi_hdr.h"

#define SECONDS_IN_TROPICAL_YEAR (365.24219 * 24 * 60 * 60)

int
main(int argc, char *argv[])
{
    time_t t;
    struct tm *gmp, *locp;
    struct tm gm, loc;
    struct timeval tv;

    /* Retrieve time, convert and display it in various forms */

    /*
        time()函数返回一个time_t类型的值，是一个有符号整数，值代表当前时间离1970.1.1零点过去的秒数
    */
    t = time(NULL);
    printf("Seconds since the Epoch (1 Jan 1970): %ld", (long) t);
    printf(" (about %6.3f years)\n", t / SECONDS_IN_TROPICAL_YEAR);

    /* 
    timeval 结构体
      struct timeval {
          time_t tv_sec;            // 从1970.1.1 零点开始的秒数
          suseconds _t tv_usec;     // 附加的毫秒 (long int)
      }
    */
    if (gettimeofday(&tv, NULL) == -1)
        errExit("gettimeofday");
    printf("  gettimeofday() returned %ld secs, %ld microsecs\n",
            (long) tv.tv_sec, (long) tv.tv_usec);

    /*
    gmp是一个指向tm结构体的指针，
        struct tm {
            int tm_sec;
            int tm_min;
            int tm_hour;
            int tm_mday;
            int tm_mon;
            int tm_year;
            int tm_wday;    // 一周内的第几天（星期天=0）
            int tm_yday;    // 一年内的第几天
            int tm_isdst;   // > 0 : 夏令时
                               = 0 : 非夏令时
                               < 0 : 尝试判定DTS在每年的这一时间是否生效
        }

        gmtime()函数能够把日历时间转换为一个对应于UTC的分解时间，也就是上面的结构体

    */
    gmp = gmtime(&t);
    if (gmp == NULL)
        errExit("gmtime");

    gm = *gmp;          /* Save local copy, since *gmp may be modified
                           by asctime() or gmtime() */
    printf("Broken down by gmtime():\n");
    printf("  year=%d mon=%d mday=%d hour=%d min=%d sec=%d ", gm.tm_year,
            gm.tm_mon, gm.tm_mday, gm.tm_hour, gm.tm_min, gm.tm_sec);
    printf("wday=%d yday=%d isdst=%d\n", gm.tm_wday, gm.tm_yday, gm.tm_isdst);

    /* The TZ environment variable will affect localtime().
       Try, for example:

                TZ=Pacific/Auckland calendar_time
    */

    /* localtime()函数会考虑时区和夏令时设置，其他和gmtime()一致 */
    locp = localtime(&t);
    if (locp == NULL)
        errExit("localtime");

    loc = *locp;        /* Save local copy */

    printf("Broken down by localtime():\n");
    printf("  year=%d mon=%d mday=%d hour=%d min=%d sec=%d ",
            loc.tm_year, loc.tm_mon, loc.tm_mday,
            loc.tm_hour, loc.tm_min, loc.tm_sec);
    printf("wday=%d yday=%d isdst=%d\n\n",
            loc.tm_wday, loc.tm_yday, loc.tm_isdst);

    /* asctime()函数 将分解后的时间格式化为字符串,参数为一个tm结构体 */
    printf("asctime() formats the gmtime() value as: %s", asctime(&gm));
    /* ctime()函数 将time_t转换为可打印格式 */
    printf("ctime() formats the time() value as:     %s", ctime(&t));

    /* mktime()函数 将一个本地时区的分解时间解释为time_t值 */
    printf("mktime() of gmtime() value:    %ld secs\n", (long) mktime(&gm));
    printf("mktime() of localtime() value: %ld secs\n", (long) mktime(&loc));

    exit(EXIT_SUCCESS);
}

1

TZ=":Pacific/Aukland" ./show_time

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#include <sys/times.h>
#include <time.h>
#include "tlpi_hdr.h"

static void             /* Display 'msg' and process times */
displayProcessTimes(const char *msg)
{
    struct tms t;
    clock_t clockTime;
    static long clockTicks = 0;

    if (msg != NULL)
        printf("%s", msg);

    if (clockTicks == 0) {      /* 获取每秒包含的时钟计时单元 */
        clockTicks = sysconf(_SC_CLK_TCK);
        if (clockTicks == -1)
            errExit("sysconf");
    }

    /*
        clock()返回调用进程使用的总的CPU时间，包括用户和系统。
        clock() 返回的时间分辨率是 CLOCKS_PER_SEC
    */
    clockTime = clock();
    if (clockTime == -1)
        errExit("clock");

    printf("        clock() returns: %ld clocks-per-sec (%.2f secs)\n",
            (long) clockTime, (double) clockTime / CLOCKS_PER_SEC);

    /* times()返回一个tms结构体
        struct tms {
            clock_t tms_utime;  // 调用者使用的用户CPU时间
            clock_t tms_stime;  // 调用者使用的系统CPU时间
            clock_t tms_cutime; // 调用者执行了系统调用wait()的所有已经终止的子进程使用的用户CPU时间
            clock_t tms_cstime; // 调用者执行了系统调用wait()的所有已经终止的子进程使用的系统CPU时间
        }

       times()返回的时间分辨率是ticks， sysconf(_SC_CLK_TCK)返回的是每秒ticks数。相除即得秒数。 
    */
    if (times(&t) == -1)
        errExit("times");
    printf("        times() yields: user CPU=%.2f; system CPU: %.2f\n",
            (double) t.tms_utime / clockTicks,
            (double) t.tms_stime / clockTicks);
}

int
main(int argc, char *argv[])
{
    int numCalls, j;

    printf("CLOCKS_PER_SEC=%ld  sysconf(_SC_CLK_TCK)=%ld\n\n",
            (long) CLOCKS_PER_SEC, sysconf(_SC_CLK_TCK));

    displayProcessTimes("At program start:\n");

    /* Call getppid() a large number of times, so that
       some user and system CPU time are consumed */

    numCalls = (argc > 1) ? getInt(argv[1], GN_GT_0, "num-calls") : 100000000;
    for (j = 0; j < numCalls; j++)
        (void) getppid();

    displayProcessTimes("After getppid() loop:\n");

    exit(EXIT_SUCCESS);
}

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double dur;
clock_t start,end;
start = clock();

foo();  // dosomething

end = clock();
dur = (double)(end - start);
printf("Use Time:%f\n",(dur/CLOCKS_PER_SEC));

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time_t t1, t2;
float diff_time;

time(&t1);

foo();  // dosomething

time(&t2);
diff_time = difftime(t2, t1);