c/c++日期时间的计算程序

Listing 1 time1.c - 采用不同格式输出当前的日期和时间

#include <stdio.h>
#include <time.h>

#define BUFSIZE 128

main()
{
   time_t tval;
   struct tm *now;
   char buf[BUFSIZE];
   char *fancy_format =
     "Or getting really fancy:\n"
     "%A, %B %d, day %j of %Y.\n"
     "The time is %I:%M %p.";

   /* Get current date and time */
   tval = time(NULL);
   now = localtime(&tval);
   printf("The current date and time:\n"
         "%d/%02d/%02d %d:%02d:%02d\n\n",
     now->tm_mon+1, now->tm_mday, now->tm_year,
     now->tm_hour, now->tm_min, now->tm_sec);
   printf("Or in default system format:\n%s\n",
         ctime(&tval));
   strftime(buf,sizeof buf,fancy_format,now);
   puts(buf);

   return 0;
}

/*  Output
The current date and time:
10/06/92 12:58:00

Or in default system format:
Tue Oct 06 12:58:00 1992

Or getting really fancy:
Tuesday, October 06, day 280 of 1992.
The time is 12:58 PM.
*/

/* End of File */

Listing 2 time2.c -展示如何计算将来某一天的日期以及以秒为单位计算出的执行时间

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

main()
{
   time_t start, stop;
   struct tm *now;
   int ndays;

   /* Get current date and time */
   time(&start);
   now = localtime(&start);

   /* Enter an interval in days */
   fputs("How many days from now? ",stderr);
   if (scanf("%d",&ndays) !=1)
      return EXIT_FAILURE;
   now->tm_mday += ndays;
   if (mktime(now) != -1)
      printf("New date: %s",asctime(now));
   else
      puts("Sorry. Can't encode your date.");

   /* Calculate elapsed time */
   time(&stop);
   printf("Elapsed program time in seconds: %f\n",
     difftime(stop,start));

   return EXIT_SUCCESS;
}

/* Output
How many days from now? 45
New date: Fri Nov 20 12:40:32 1992
Elapsed program time in seconds: 1.000000
*/

/* End of File */

Listing 3 date.h - 一个简单的日期结构

struct Date
{
   int day;
   int month;
   int year;
};
typedef struct Date Date;

Date* date_interval(const Date *, const Date *);
/* End of File */

Listing 4 date_int.c - 计算两个日期的间隔

/* date_int.c: Compute duration between two dates */

#include "date.h"

#define isleap(y) \
 ((y)%4 == 0 && (y)%100 != 0 || (y)%400 == 0)

static int Dtab [2][13] =
{
  {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
  {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};

Date *date_interval(const Date *d1, const Date *d2)
{
   static Date result;
   int months, days, years, prev_month;

   /* Compute the interval - assume d1 precedes d2 */
   years = d2->year - d1->year;
   months = d2->month - d1->month;
   days = d2->day - d1->day;

   /* Do obvious corrections (days before months!)
    *
    * This is a loop in case the previous month is
    * February, and days < -28.
    */
   prev_month = d2->month - 1;
   while (days < 0)
   {
      /* Borrow from the previous month */
      if (prev_month == 0)
         prev_month = 12;
      --months;
      days += Dtab[isleap(d2->year)][prev_month--];
   }

   if (months < 0)
   {
      /* Borrow from the previous year */
      --years;
      months += 12;
   }

   /* Prepare output */
   result.month = months;
   result.day = days;
   result.year = years;
   return &result;
}
/* End of File */

Listing 5 tdate.c - 举例说明日期间隔函数的使用

/* tdate.c: Test date_interval() */

#include <stdio.h>
#include <stdlib.h>
#include "date.h"

main()
{
   Date d1, d2, *result;
   int nargs;

   /* Read in two dates - assume 1st precedes 2nd */
   fputs("Enter a date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &d1.month,
     &d1.day, &d1.year);
   if (nargs != 3)
      return EXIT_FAILURE;

   fputs("Enter a later date, MM/DD/YY> ",stderr);
   nargs = scanf("%d/%d/%d%*c", &d2.month,
     &d2.day, &d2.year);
   if (nargs != 3)
      return EXIT_FAILURE;

   /* Compute interval in years, months, and days */
   result = date_interval(&d1, &d2);
   printf("years: %d, months: %d, days: %d\n",
      result->year, result->month, result->day);
   return EXIT_SUCCESS;

}
/* Sample Execution:
Enter a date, MM/DD/YY> 10/1/51
Enter a later date, MM/DD/YY> 10/6/92
years: 41, months: 0, days: 5 */
/* End of File */

Listing 6 ftime.c - 确定是否time1.c比time2.c更新

/* ftime.c: Compare file time stamps */

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <time.h>

main()
{
   struct stat fs1, fs2;

   if (stat("time1.c",&fs1) == 0 &&
      stat("time2.c",&fs2) == 0)
   {
      double interval =
        difftime(fs2.st_mtime,fs1.st_mtime);

      printf("time1.c %s newer than time2.c\n",
        (interval < 0.0) ? "is" : "is not");
      return EXIT_SUCCESS;
   }
   else
      return EXIT_FAILURE;
}
/* Output
time1.c is not newer than time2.c */
/* End of File */

Listing 7 touch.c -通过覆盖旧文件或者创建一个新的文件来更新时间戳

/* touch.c: Update a file's time stamp */

#include <stdio.h>

void touch(char *fname)
{
   FILE *f = fopen(fname,"r+b");
   if (f != NULL)
   {
      char c = getc(f);
      rewind(f);
      putc(c,f);
   }
   else
      fopen(fname,"wb");

   fclose(f);
}

/* End of File */