strftime.c

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/* strftime - formatted time and date to a string */
/*
 * Modified slightly by Chet Ramey for inclusion in Bash
 */
/*
 * strftime.c
 *
 * Public-domain implementation of ISO C library routine.
 *
 * If you can't do prototypes, get GCC.
 *
 * The C99 standard now specifies just about all of the formats
 * that were additional in the earlier versions of this file.
 *
 * For extensions from SunOS, add SUNOS_EXT.
 * For extensions from HP/UX, add HPUX_EXT.
 * For VMS dates, add VMS_EXT.
 * For complete POSIX semantics, add POSIX_SEMANTICS.
 *
 * The code for %c, %x, and %X follows the C99 specification for
 * the "C" locale.
 *
 * This version ignores LOCALE information.
 * It also doesn't worry about multi-byte characters.
 * So there.
 *
 * Arnold Robbins
 * January, February, March, 1991
 * Updated March, April 1992
 * Updated April, 1993
 * Updated February, 1994
 * Updated May, 1994
 * Updated January, 1995
 * Updated September, 1995
 * Updated January, 1996
 * Updated July, 1997
 * Updated October, 1999
 * Updated September, 2000
 * Updated December, 2001
 * Updated January, 2011
 * Updated April, 2012
 *
 * Fixes from ado@elsie.nci.nih.gov,
 * February 1991, May 1992
 * Fixes from Tor Lillqvist tml@tik.vtt.fi,
 * May 1993
 * Further fixes from ado@elsie.nci.nih.gov,
 * February 1994
 * %z code from chip@chinacat.unicom.com,
 * Applied September 1995
 * %V code fixed (again) and %G, %g added,
 * January 1996
 * %v code fixed, better configuration,
 * July 1997
 * Moved to C99 specification.
 * September 2000
 * Fixes from Tanaka Akira <akr@m17n.org>
 * December 2001
 */
#include <config.h>

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

#if defined(TM_IN_SYS_TIME)
#include <sys/types.h>
#include <sys/time.h>
#endif

#include <stdlib.h>
#include <string.h>

/* defaults: season to taste */
#define SUNOS_EXT   1   /* stuff in SunOS strftime routine */
#define VMS_EXT     1   /* include %v for VMS date format */
#define HPUX_EXT    1   /* non-conflicting stuff in HP-UX date */
#define POSIX_SEMANTICS 1   /* call tzset() if TZ changes */
#define POSIX_2008  1   /* flag and fw for C, F, G, Y formats */

#undef strchr   /* avoid AIX weirdness */

#if defined (SHELL)
extern char *get_string_value (const char *);
#endif

extern void tzset(void);
static int weeknumber(const struct tm *timeptr, int firstweekday);
static int iso8601wknum(const struct tm *timeptr);

#ifndef inline
#ifdef __GNUC__
#define inline  __inline__
#else
#define inline  /**/
#endif
#endif

#define range(low, item, hi)    max(low, min(item, hi))

/* Whew! This stuff is a mess. */
#if !defined(OS2) && !defined(MSDOS) && !defined(__CYGWIN__) && defined(HAVE_TZNAME)
extern char *tzname[2];
extern int daylight;
#if defined(SOLARIS) || defined(mips) || defined (M_UNIX)
extern long int timezone, altzone;
#else
#  if defined (HPUX) || defined(__hpux)
extern long int timezone;
#  else
#    if !defined(__CYGWIN__)
extern int timezone, altzone;
#    endif
#  endif
#endif
#endif

#undef min  /* just in case */

/* min --- return minimum of two numbers */

static inline int
min(int a, int b)
{
    return (a < b ? a : b);
}

#undef max  /* also, just in case */

/* max --- return maximum of two numbers */

static inline int
max(int a, int b)
{
    return (a > b ? a : b);
}

#ifdef POSIX_2008
/* iso_8601_2000_year --- format a year per ISO 8601:2000 as in 1003.1 */

static void
iso_8601_2000_year(char *buf, int year, size_t fw)
{
    int extra;
    char sign = '\0';

    if (year >= -9999 && year <= 9999) {
        sprintf(buf, "%0*d", (int) fw, year);
        return;
    }

    /* now things get weird */
    if (year > 9999) {
        sign = '+';
    } else {
        sign = '-';
        year = -year;
    }

    extra = year / 10000;
    year %= 10000;
    sprintf(buf, "%c_%04d_%d", sign, extra, year);
}
#endif /* POSIX_2008 */

/* strftime --- produce formatted time */

size_t
strftime(char *s, size_t maxsize, const char *format, const struct tm *timeptr)
{
    char *endp = s + maxsize;
    char *start = s;
    auto char tbuf[100];
    long off;
    int i, w;
    long y;
    static short first = 1;
#ifdef POSIX_SEMANTICS
    static char *savetz = NULL;
    static int savetzlen = 0;
    char *tz;
#endif /* POSIX_SEMANTICS */
#ifndef HAVE_TM_ZONE
#ifndef HAVE_TM_NAME
#ifndef HAVE_TZNAME
#ifndef __CYGWIN__
    extern char *timezone();
    struct timeval tv;
    struct timezone zone;
#endif /* __CYGWIN__ */
#endif /* HAVE_TZNAME */
#endif /* HAVE_TM_NAME */
#endif /* HAVE_TM_ZONE */
#ifdef POSIX_2008
    int pad;
    size_t fw;
    char flag;
#endif /* POSIX_2008 */

    /* various tables, useful in North America */
    static const char *days_a[] = {
        "Sun", "Mon", "Tue", "Wed",
        "Thu", "Fri", "Sat",
    };
    static const char *days_l[] = {
        "Sunday", "Monday", "Tuesday", "Wednesday",
        "Thursday", "Friday", "Saturday",
    };
    static const char *months_a[] = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun",
        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
    };
    static const char *months_l[] = {
        "January", "February", "March", "April",
        "May", "June", "July", "August", "September",
        "October", "November", "December",
    };
    static const char *ampm[] = { "AM", "PM", };

    if (s == NULL || format == NULL || timeptr == NULL || maxsize == 0)
        return 0;

    /* quick check if we even need to bother */
    if (strchr(format, '%') == NULL && strlen(format) + 1 >= maxsize)
        return 0;

#ifndef POSIX_SEMANTICS
    if (first) {
        tzset();
        first = 0;
    }
#else   /* POSIX_SEMANTICS */
#if defined (SHELL)
    tz = get_string_value ("TZ");
#else
    tz = getenv("TZ");
#endif
    if (first) {
        if (tz != NULL) {
            int tzlen = strlen(tz);

            savetz = (char *) malloc(tzlen + 1);
            if (savetz != NULL) {
                savetzlen = tzlen + 1;
                strcpy(savetz, tz);
            }
        }
        tzset();
        first = 0;
    }
    /* if we have a saved TZ, and it is different, recapture and reset */
    if (tz && savetz && (tz[0] != savetz[0] || strcmp(tz, savetz) != 0)) {
        i = strlen(tz) + 1;
        if (i > savetzlen) {
            savetz = (char *) realloc(savetz, i);
            if (savetz) {
                savetzlen = i;
                strcpy(savetz, tz);
            }
        } else
            strcpy(savetz, tz);
        tzset();
    }
#endif  /* POSIX_SEMANTICS */

    for (; *format && s < endp - 1; format++) {
        tbuf[0] = '\0';
        if (*format != '%') {
            *s++ = *format;
            continue;
        }
#ifdef POSIX_2008
        pad = '\0';
        fw = 0;
        flag = '\0';
        switch (*++format) {
        case '+':
            flag = '+';
            /* fall through */
        case '0':
            pad = '0';
            format++;
            break;

        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
            break;

        default:
            format--;
            goto again;
        }
        for (; isdigit(*format); format++) {
            fw = fw * 10 + (*format - '0');
        }
        format--;
#endif /* POSIX_2008 */

    again:
        switch (*++format) {
        case '\0':
            *s++ = '%';
            goto out;

        case '%':
            *s++ = '%';
            continue;

        case 'a':   /* abbreviated weekday name */
            if (timeptr->tm_wday < 0 || timeptr->tm_wday > 6)
                strcpy(tbuf, "?");
            else
                strcpy(tbuf, days_a[timeptr->tm_wday]);
            break;

        case 'A':   /* full weekday name */
            if (timeptr->tm_wday < 0 || timeptr->tm_wday > 6)
                strcpy(tbuf, "?");
            else
                strcpy(tbuf, days_l[timeptr->tm_wday]);
            break;

        case 'b':   /* abbreviated month name */
        short_month:
            if (timeptr->tm_mon < 0 || timeptr->tm_mon > 11)
                strcpy(tbuf, "?");
            else
                strcpy(tbuf, months_a[timeptr->tm_mon]);
            break;

        case 'B':   /* full month name */
            if (timeptr->tm_mon < 0 || timeptr->tm_mon > 11)
                strcpy(tbuf, "?");
            else
                strcpy(tbuf, months_l[timeptr->tm_mon]);
            break;

        case 'c':   /* appropriate date and time representation */
            /*
             * This used to be:
             *
             * strftime(tbuf, sizeof tbuf, "%a %b %e %H:%M:%S %Y", timeptr);
             *
             * Now, per the ISO 1999 C standard, it this:
             */
            strftime(tbuf, sizeof tbuf, "%A %B %d %T %Y", timeptr);
            break;

        case 'C':
#ifdef POSIX_2008
            if (pad != '\0' && fw > 0) {
                size_t min_fw = (flag ? 3 : 2);

                fw = max(fw, min_fw);
                sprintf(tbuf, flag
                        ? "%+0*ld"
                        : "%0*ld", (int) fw,
                        (timeptr->tm_year + 1900L) / 100);
            } else
#endif /* POSIX_2008 */
        century:
                sprintf(tbuf, "%02ld", (timeptr->tm_year + 1900L) / 100);
            break;

        case 'd':   /* day of the month, 01 - 31 */
            i = range(1, timeptr->tm_mday, 31);
            sprintf(tbuf, "%02d", i);
            break;

        case 'D':   /* date as %m/%d/%y */
            strftime(tbuf, sizeof tbuf, "%m/%d/%y", timeptr);
            break;

        case 'e':   /* day of month, blank padded */
            sprintf(tbuf, "%2d", range(1, timeptr->tm_mday, 31));
            break;

        case 'E':
            /* POSIX (now C99) locale extensions, ignored for now */
            goto again;

        case 'F':   /* ISO 8601 date representation */
        {
#ifdef POSIX_2008
            /*
             * Field width for %F is for the whole thing.
             * It must be at least 10.
             */
            char m_d[10];
            strftime(m_d, sizeof m_d, "-%m-%d", timeptr);
            size_t min_fw = 10;

            if (pad != '\0' && fw > 0) {
                fw = max(fw, min_fw);
            } else {
                fw = min_fw;
            }

            fw -= 6;    /* -XX-XX at end are invariant */

            iso_8601_2000_year(tbuf, timeptr->tm_year + 1900, fw);
            strcat(tbuf, m_d);
#else
            strftime(tbuf, sizeof tbuf, "%Y-%m-%d", timeptr);
#endif /* POSIX_2008 */
        }
            break;

        case 'g':
        case 'G':
            /*
             * Year of ISO week.
             *
             * If it's December but the ISO week number is one,
             * that week is in next year.
             * If it's January but the ISO week number is 52 or
             * 53, that week is in last year.
             * Otherwise, it's this year.
             */
            w = iso8601wknum(timeptr);
            if (timeptr->tm_mon == 11 && w == 1)
                y = 1900L + timeptr->tm_year + 1;
            else if (timeptr->tm_mon == 0 && w >= 52)
                y = 1900L + timeptr->tm_year - 1;
            else
                y = 1900L + timeptr->tm_year;

            if (*format == 'G') {
#ifdef POSIX_2008
                if (pad != '\0' && fw > 0) {
                    size_t min_fw = 4;

                    fw = max(fw, min_fw);
                    sprintf(tbuf, flag
                            ? "%+0*ld"
                            : "%0*ld", (int) fw,
                            y);
                } else
#endif /* POSIX_2008 */
                    sprintf(tbuf, "%ld", y);
            }
            else
                sprintf(tbuf, "%02ld", y % 100);
            break;

        case 'h':   /* abbreviated month name */
            goto short_month;

        case 'H':   /* hour, 24-hour clock, 00 - 23 */
            i = range(0, timeptr->tm_hour, 23);
            sprintf(tbuf, "%02d", i);
            break;

        case 'I':   /* hour, 12-hour clock, 01 - 12 */
            i = range(0, timeptr->tm_hour, 23);
            if (i == 0)
                i = 12;
            else if (i > 12)
                i -= 12;
            sprintf(tbuf, "%02d", i);
            break;

        case 'j':   /* day of the year, 001 - 366 */
            sprintf(tbuf, "%03d", timeptr->tm_yday + 1);
            break;

        case 'm':   /* month, 01 - 12 */
            i = range(0, timeptr->tm_mon, 11);
            sprintf(tbuf, "%02d", i + 1);
            break;

        case 'M':   /* minute, 00 - 59 */
            i = range(0, timeptr->tm_min, 59);
            sprintf(tbuf, "%02d", i);
            break;

        case 'n':   /* same as \n */
            tbuf[0] = '\n';
            tbuf[1] = '\0';
            break;

        case 'O':
            /* POSIX (now C99) locale extensions, ignored for now */
            goto again;

        case 'p':   /* am or pm based on 12-hour clock */
            i = range(0, timeptr->tm_hour, 23);
            if (i < 12)
                strcpy(tbuf, ampm[0]);
            else
                strcpy(tbuf, ampm[1]);
            break;

        case 'r':   /* time as %I:%M:%S %p */
            strftime(tbuf, sizeof tbuf, "%I:%M:%S %p", timeptr);
            break;

        case 'R':   /* time as %H:%M */
            strftime(tbuf, sizeof tbuf, "%H:%M", timeptr);
            break;

#if defined(HAVE_MKTIME)
        case 's':   /* time as seconds since the Epoch */
        {
            struct tm non_const_timeptr;

            non_const_timeptr = *timeptr;
            sprintf(tbuf, "%ld", mktime(& non_const_timeptr));
            break;
        }
#endif /* defined(HAVE_MKTIME) */

        case 'S':   /* second, 00 - 60 */
            i = range(0, timeptr->tm_sec, 60);
            sprintf(tbuf, "%02d", i);
            break;

        case 't':   /* same as \t */
            tbuf[0] = '\t';
            tbuf[1] = '\0';
            break;

        case 'T':   /* time as %H:%M:%S */
        the_time:
            strftime(tbuf, sizeof tbuf, "%H:%M:%S", timeptr);
            break;

        case 'u':
        /* ISO 8601: Weekday as a decimal number [1 (Monday) - 7] */
            sprintf(tbuf, "%d", timeptr->tm_wday == 0 ? 7 :
                    timeptr->tm_wday);
            break;

        case 'U':   /* week of year, Sunday is first day of week */
            sprintf(tbuf, "%02d", weeknumber(timeptr, 0));
            break;

        case 'V':   /* week of year according ISO 8601 */
            sprintf(tbuf, "%02d", iso8601wknum(timeptr));
            break;

        case 'w':   /* weekday, Sunday == 0, 0 - 6 */
            i = range(0, timeptr->tm_wday, 6);
            sprintf(tbuf, "%d", i);
            break;

        case 'W':   /* week of year, Monday is first day of week */
            sprintf(tbuf, "%02d", weeknumber(timeptr, 1));
            break;

        case 'x':   /* appropriate date representation */
            strftime(tbuf, sizeof tbuf, "%A %B %d %Y", timeptr);
            break;

        case 'X':   /* appropriate time representation */
            goto the_time;
            break;

        case 'y':   /* year without a century, 00 - 99 */
        year:
            i = timeptr->tm_year % 100;
            sprintf(tbuf, "%02d", i);
            break;

        case 'Y':   /* year with century */
#ifdef POSIX_2008
            if (pad != '\0' && fw > 0) {
                size_t min_fw = 4;

                fw = max(fw, min_fw);
                sprintf(tbuf, flag
                        ? "%+0*ld"
                        : "%0*ld", (int) fw,
                        1900L + timeptr->tm_year);
            } else
#endif /* POSIX_2008 */
            sprintf(tbuf, "%ld", 1900L + timeptr->tm_year);
            break;

        /*
         * From: Chip Rosenthal <chip@chinacat.unicom.com>
         * Date: Sun, 19 Mar 1995 00:33:29 -0600 (CST)
         * 
         * Warning: the %z [code] is implemented by inspecting the
         * timezone name conditional compile settings, and
         * inferring a method to get timezone offsets. I've tried
         * this code on a couple of machines, but I don't doubt
         * there is some system out there that won't like it.
         * Maybe the easiest thing to do would be to bracket this
         * with an #ifdef that can turn it off. The %z feature
         * would be an admittedly obscure one that most folks can
         * live without, but it would be a great help to those of
         * us that muck around with various message processors.
         */
        case 'z':   /* time zone offset east of GMT e.g. -0600 */
            if (timeptr->tm_isdst < 0)
                break;
#ifdef HAVE_TM_NAME
            /*
             * Systems with tm_name probably have tm_tzadj as
             * secs west of GMT.  Convert to mins east of GMT.
             */
            off = -timeptr->tm_tzadj / 60;
#else /* !HAVE_TM_NAME */
#ifdef HAVE_TM_ZONE
            /*
             * Systems with tm_zone probably have tm_gmtoff as
             * secs east of GMT.  Convert to mins east of GMT.
             */
            off = timeptr->tm_gmtoff / 60;
#else /* !HAVE_TM_ZONE */
#if HAVE_TZNAME
            /*
             * Systems with tzname[] probably have timezone as
             * secs west of GMT.  Convert to mins east of GMT.
             */
#  if defined(__hpux) || defined (HPUX) || defined(__CYGWIN__)
            off = -timezone / 60;
#  else
            /* ADR: 4 August 2001, fixed this per gazelle@interaccess.com */
            off = -(daylight ? altzone : timezone) / 60;
#  endif
#else /* !HAVE_TZNAME */
            gettimeofday(& tv, & zone);
            off = -zone.tz_minuteswest;
#endif /* !HAVE_TZNAME */
#endif /* !HAVE_TM_ZONE */
#endif /* !HAVE_TM_NAME */
            if (off < 0) {
                tbuf[0] = '-';
                off = -off;
            } else {
                tbuf[0] = '+';
            }
            sprintf(tbuf+1, "%02ld%02ld", off/60, off%60);
            break;

        case 'Z':   /* time zone name or abbrevation */
#ifdef HAVE_TZNAME
            i = (daylight && timeptr->tm_isdst > 0); /* 0 or 1 */
            strcpy(tbuf, tzname[i]);
#else
#ifdef HAVE_TM_ZONE
            strcpy(tbuf, timeptr->tm_zone);
#else
#ifdef HAVE_TM_NAME
            strcpy(tbuf, timeptr->tm_name);
#else
            gettimeofday(& tv, & zone);
            strcpy(tbuf, timezone(zone.tz_minuteswest,
                        timeptr->tm_isdst > 0));
#endif /* HAVE_TM_NAME */
#endif /* HAVE_TM_ZONE */
#endif /* HAVE_TZNAME */
            break;

#ifdef SUNOS_EXT
        case 'k':   /* hour, 24-hour clock, blank pad */
            sprintf(tbuf, "%2d", range(0, timeptr->tm_hour, 23));
            break;

        case 'l':   /* hour, 12-hour clock, 1 - 12, blank pad */
            i = range(0, timeptr->tm_hour, 23);
            if (i == 0)
                i = 12;
            else if (i > 12)
                i -= 12;
            sprintf(tbuf, "%2d", i);
            break;
#endif

#ifdef HPUX_EXT
        case 'N':   /* Emperor/Era name */
            /* this is essentially the same as the century */
            goto century;   /* %C */

        case 'o':   /* Emperor/Era year */
            goto year;  /* %y */
#endif /* HPUX_EXT */


#ifdef VMS_EXT
        case 'v':   /* date as dd-bbb-YYYY */
            sprintf(tbuf, "%2d-%3.3s-%4ld",
                range(1, timeptr->tm_mday, 31),
                months_a[range(0, timeptr->tm_mon, 11)],
                timeptr->tm_year + 1900L);
            for (i = 3; i < 6; i++)
                if (islower(tbuf[i]))
                    tbuf[i] = toupper(tbuf[i]);
            break;
#endif

        default:
            tbuf[0] = '%';
            tbuf[1] = *format;
            tbuf[2] = '\0';
            break;
        }
        i = strlen(tbuf);
        if (i) {
            if (s + i < endp - 1) {
                strcpy(s, tbuf);
                s += i;
            } else
                return 0;
        }
    }
out:
    if (s < endp && *format == '\0') {
        *s = '\0';
        return (s - start);
    } else
        return 0;
}

/* isleap --- is a year a leap year? */

static int
isleap(long year)
{
    return ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0);
}


/* iso8601wknum --- compute week number according to ISO 8601 */

static int
iso8601wknum(const struct tm *timeptr)
{
    /*
     * From 1003.2:
     *  If the week (Monday to Sunday) containing January 1
     *  has four or more days in the new year, then it is week 1;
     *  otherwise it is the highest numbered week of the previous
     *  year (52 or 53), and the next week is week 1.
     *
     * ADR: This means if Jan 1 was Monday through Thursday,
     *  it was week 1, otherwise week 52 or 53.
     *
     * XPG4 erroneously included POSIX.2 rationale text in the
     * main body of the standard. Thus it requires week 53.
     */

    int weeknum, jan1day, diff;

    /* get week number, Monday as first day of the week */
    weeknum = weeknumber(timeptr, 1);

    /*
     * With thanks and tip of the hatlo to tml@tik.vtt.fi
     *
     * What day of the week does January 1 fall on?
     * We know that
     *  (timeptr->tm_yday - jan1.tm_yday) MOD 7 ==
     *      (timeptr->tm_wday - jan1.tm_wday) MOD 7
     * and that
     *  jan1.tm_yday == 0
     * and that
     *  timeptr->tm_wday MOD 7 == timeptr->tm_wday
     * from which it follows that. . .
     */
    jan1day = timeptr->tm_wday - (timeptr->tm_yday % 7);
    if (jan1day < 0)
        jan1day += 7;

    /*
     * If Jan 1 was a Monday through Thursday, it was in
     * week 1.  Otherwise it was last year's highest week, which is
     * this year's week 0.
     *
     * What does that mean?
     * If Jan 1 was Monday, the week number is exactly right, it can
     *  never be 0.
     * If it was Tuesday through Thursday, the weeknumber is one
     *  less than it should be, so we add one.
     * Otherwise, Friday, Saturday or Sunday, the week number is
     * OK, but if it is 0, it needs to be 52 or 53.
     */
    switch (jan1day) {
    case 1:     /* Monday */
        break;
    case 2:     /* Tuesday */
    case 3:     /* Wednesday */
    case 4:     /* Thursday */
        weeknum++;
        break;
    case 5:     /* Friday */
    case 6:     /* Saturday */
    case 0:     /* Sunday */
        if (weeknum == 0) {
#ifdef USE_BROKEN_XPG4
            /* XPG4 (as of March 1994) says 53 unconditionally */
            weeknum = 53;
#else
            /* get week number of last week of last year */
            struct tm dec31ly;  /* 12/31 last year */
            dec31ly = *timeptr;
            dec31ly.tm_year--;
            dec31ly.tm_mon = 11;
            dec31ly.tm_mday = 31;
            dec31ly.tm_wday = (jan1day == 0) ? 6 : jan1day - 1;
            dec31ly.tm_yday = 364 + isleap(dec31ly.tm_year + 1900L);
            weeknum = iso8601wknum(& dec31ly);
#endif
        }
        break;
    }

    if (timeptr->tm_mon == 11) {
        /*
         * The last week of the year
         * can be in week 1 of next year.
         * Sigh.
         *
         * This can only happen if
         *  M   T  W
         *  29  30 31
         *  30  31
         *  31
         */
        int wday, mday;

        wday = timeptr->tm_wday;
        mday = timeptr->tm_mday;
        if (   (wday == 1 && (mday >= 29 && mday <= 31))
            || (wday == 2 && (mday == 30 || mday == 31))
            || (wday == 3 &&  mday == 31))
            weeknum = 1;
    }

    return weeknum;
}

/* weeknumber --- figure how many weeks into the year */

/* With thanks and tip of the hatlo to ado@elsie.nci.nih.gov */

static int
weeknumber(const struct tm *timeptr, int firstweekday)
{
    int wday = timeptr->tm_wday;
    int ret;

    if (firstweekday == 1) {
        if (wday == 0)  /* sunday */
            wday = 6;
        else
            wday--;
    }
    ret = ((timeptr->tm_yday + 7 - wday) / 7);
    if (ret < 0)
        ret = 0;
    return ret;
}

#if 0
/* ADR --- I'm loathe to mess with ado's code ... */

Date:         Wed, 24 Apr 91 20:54:08 MDT
From: Michal Jaegermann <audfax!emory!vm.ucs.UAlberta.CA!NTOMCZAK>
To: arnold@audiofax.com

Hi Arnold,
in a process of fixing of strftime() in libraries on Atari ST I grabbed
some pieces of code from your own strftime.  When doing that it came
to mind that your weeknumber() function compiles a little bit nicer
in the following form:
/*
 * firstweekday is 0 if starting in Sunday, non-zero if in Monday
 */
{
    return (timeptr->tm_yday - timeptr->tm_wday +
        (firstweekday ? (timeptr->tm_wday ? 8 : 1) : 7)) / 7;
}
How nicer it depends on a compiler, of course, but always a tiny bit.

   Cheers,
   Michal
   ntomczak@vm.ucs.ualberta.ca
#endif

#ifdef  TEST_STRFTIME

/*
 * NAME:
 *  tst
 *
 * SYNOPSIS:
 *  tst
 *
 * DESCRIPTION:
 *  "tst" is a test driver for the function "strftime".
 *
 * OPTIONS:
 *  None.
 *
 * AUTHOR:
 *  Karl Vogel
 *  Control Data Systems, Inc.
 *  vogelke@c-17igp.wpafb.af.mil
 *
 * BUGS:
 *  None noticed yet.
 *
 * COMPILE:
 *  cc -o tst -DTEST_STRFTIME strftime.c
 */

/* ADR: I reformatted this to my liking, and deleted some unneeded code. */

#ifndef NULL
#include    <stdio.h>
#endif
#include    <sys/time.h>
#include    <string.h>

#define     MAXTIME     132

/*
 * Array of time formats.
 */

static char *array[] =
{
    "(%%A)      full weekday name, var length (Sunday..Saturday)  %A",
    "(%%B)       full month name, var length (January..December)  %B",
    "(%%C)                                               Century  %C",
    "(%%D)                                       date (%%m/%%d/%%y)  %D",
    "(%%E)                           Locale extensions (ignored)  %E",
    "(%%F)       full month name, var length (January..December)  %F",
    "(%%H)                          hour (24-hour clock, 00..23)  %H",
    "(%%I)                          hour (12-hour clock, 01..12)  %I",
    "(%%M)                                       minute (00..59)  %M",
    "(%%N)                                      Emporer/Era Name  %N",
    "(%%O)                           Locale extensions (ignored)  %O",
    "(%%R)                                 time, 24-hour (%%H:%%M)  %R",
    "(%%S)                                       second (00..60)  %S",
    "(%%T)                              time, 24-hour (%%H:%%M:%%S)  %T",
    "(%%U)    week of year, Sunday as first day of week (00..53)  %U",
    "(%%V)                    week of year according to ISO 8601  %V",
    "(%%W)    week of year, Monday as first day of week (00..53)  %W",
    "(%%X)     appropriate locale time representation (%H:%M:%S)  %X",
    "(%%Y)                           year with century (1970...)  %Y",
    "(%%Z) timezone (EDT), or blank if timezone not determinable  %Z",
    "(%%a)          locale's abbreviated weekday name (Sun..Sat)  %a",
    "(%%b)            locale's abbreviated month name (Jan..Dec)  %b",
    "(%%c)           full date (Sat Nov  4 12:02:33 1989)%n%t%t%t  %c",
    "(%%d)                             day of the month (01..31)  %d",
    "(%%e)               day of the month, blank-padded ( 1..31)  %e",
    "(%%h)                                should be same as (%%b)  %h",
    "(%%j)                            day of the year (001..366)  %j",
    "(%%k)               hour, 24-hour clock, blank pad ( 0..23)  %k",
    "(%%l)               hour, 12-hour clock, blank pad ( 0..12)  %l",
    "(%%m)                                        month (01..12)  %m",
    "(%%o)                                      Emporer/Era Year  %o",
    "(%%p)              locale's AM or PM based on 12-hour clock  %p",
    "(%%r)                   time, 12-hour (same as %%I:%%M:%%S %%p)  %r",
    "(%%u) ISO 8601: Weekday as decimal number [1 (Monday) - 7]   %u",
    "(%%v)                                VMS date (dd-bbb-YYYY)  %v",
    "(%%w)                       day of week (0..6, Sunday == 0)  %w",
    "(%%x)                appropriate locale date representation  %x",
    "(%%y)                      last two digits of year (00..99)  %y",
    "(%%z)      timezone offset east of GMT as HHMM (e.g. -0500)  %z",
    (char *) NULL
};

/* main routine. */

int
main(argc, argv)
int argc;
char **argv;
{
    long time();

    char *next;
    char string[MAXTIME];

    int k;
    int length;

    struct tm *tm;

    long clock;

    /* Call the function. */

    clock = time((long *) 0);
    tm = localtime(&clock);

    for (k = 0; next = array[k]; k++) {
        length = strftime(string, MAXTIME, next, tm);
        printf("%s\n", string);
    }

    exit(0);
}
#endif  /* TEST_STRFTIME */