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 */