69 lines
2.0 KiB
C
69 lines
2.0 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#define HELP_STR "usage: name year [month] day"
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int month_day(int year, int day, int *pmonth);
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int day_of_year(int year, int month, int day);
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/* converts arguments year yearday to year month day or
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* year month day to year yearday */
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int main(int argc, char *argv[])
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{
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int y, m, d, yd;
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if (argc == 3) { /* year day -> month day */
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y = atoi(argv[1]), yd = atoi(argv[2]);
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if ((d = month_day(y, yd, &m))) {
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printf("%d %d %d\n", y, m, d);
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return 0;
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}
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printf("error: invalid yearday %d\n", yd);
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} else if (argc == 4) { /* year month day -> year day */
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y = atoi(argv[1]), m = atoi(argv[2]), d = atoi(argv[3]);
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if ((yd = day_of_year(y, m, d))) {
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printf("%d %d\n", y, yd);
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return 0;
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}
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printf("error: invalid month %d or day %d\n", m, d);
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}
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puts(HELP_STR);
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return 1;
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}
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static char daytab[][13] = {
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{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
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{0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
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};
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#define IS_LEAP(Y) (Y%4 == 0 && Y%100 != 0 || Y%400 == 0)
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#define IS_MONTH(M) (0 < M && M <= 12)
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#define IS_D_OF_M(LEAP, M, D) (0 < D && D <= daytab[LEAP][M])
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#define IS_YD_OF_Y(LEAP, YD) (0 < YD && YD <= 365+LEAP)
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/* day_of_year: set day of year from month & day
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* return day of year or 0 on error */
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int day_of_year(int year, int month, int day)
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{
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int m, leap = IS_LEAP(year);
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if (!IS_MONTH(month) || !IS_D_OF_M(leap, month, day))
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/* validity check */
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return 0;
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for (m = 1; m < month; m++)
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day += daytab[leap][m];
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return day;
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}
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/* month_day: set month, day from day of year
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* return day of month or 0 on error, set pmonth to month */
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int month_day(int year, int yearday, int *pmonth)
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{
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int m, leap = IS_LEAP(year);
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if (!IS_YD_OF_Y(leap, yearday)) /* validity check */
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return 0;
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for (m = 1; yearday > daytab[leap][m]; m++)
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yearday -= daytab[leap][m];
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*pmonth = m;
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return yearday;
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}
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