/*** *localtim.c - Convert time_t value to time structure * * Copyright (c) 1985-1993, Microsoft Corporation. All rights reserved. * *Purpose: * Converts time stored as a time_t value to a structure of type * struct tm expressed as local time. * *Revision History: * 01-??-84 RLB Module created * 05-??-84 DCW split off from the rest of the ctime routines * 02-18-87 JCR made localtime work when gmtime returns null * 03-31-87 JCR fixed bug pertaining to uninitialized _isindst(tb) * 04-10-87 JCR changed long declaration to time_t and added const * 11-10-87 SKS Removed IBMC20 switch * 11-18-87 SKS Change tzset() to __tzset() * 12-11-87 JCR Added "_LOAD_DS" to declaration * 11-06-89 KRS Added (unsigned) to handle years 2040-2099 correctly. * 03-20-90 GJF Replaced _LOAD_DS with _CALLTYPE1, added #include * , removed #include and * fixed the copyright. Also, cleaned up the formatting * a bit. * 10-04-90 GJF New-style function declarator. Also, rewrote expr. * to avoid using cast as lvalue. * 01-21-91 GJF ANSI naming. * 08-10-92 PBS Posix support (TZ stuff). * 03-24-93 GJF Ported C8-16 version and adapted for exotic Daylight * Savings Time conversions which are legal under POSIX. * 07-15-93 GJF Replaced _tzset() call with __tzset() call. * *******************************************************************************/ #include #include #include #include #include #include /*** *struct tm *localtime(ptime) - convert time_t value to tm structure * *Purpose: * Convert a value in internal (time_t) format to a tm struct * containing the corresponding local time. * * NOTES: * (1) gmtime must be called before _isindst to ensure that the tb time * structure is initialized. * (2) gmtime and localtime use a single statically allocated buffer. * Each call to one of these routines destroys the contents of the * previous call. * (3) It is assumed that time_t is a 32-bit long integer representing * the number of seconds since 00:00:00, 01-01-70 (UTC) (i.e., the * Posix/Unix Epoch. Only non-negative values are supported. * (4) It is assumed that the maximum adjustment for local time is * less than three days (include Daylight Savings Time adjustment). * This only a concern in Posix where the specification of the TZ * environment restricts the combined offset for time zone and * Daylight Savings Time to 2 * (24:59:59), just under 50 hours. * *Entry: * time_t *ptime - pointer to a long time value * *Exit: * If *ptime is non-negative, returns a pointer to the tm structure. * Otherwise, returns NULL. * *Exceptions: * See items (3) and (4) in the NOTES above. If these assumptions are * violated, behavior is undefined. * *******************************************************************************/ struct tm * _CRTAPI1 localtime ( const time_t *ptime ) { REG1 struct tm *ptm; long ltime; /* * Check for illegal time_t value */ if ( (long)*ptime < 0L ) return( NULL ); #ifdef _POSIX_ tzset(); #else __tzset(); #endif if ( (*ptime > 3 * _DAY_SEC) && (*ptime < LONG_MAX - 3 * _DAY_SEC) ) { /* * The date does not fall within the first three, or last * three, representable days of the Epoch. Therefore, there * is no possibility of overflowing or underflowing the * time_t representation as we compensate for timezone and * Daylight Savings Time. */ ltime = (long)*ptime - _timezone; ptm = gmtime( <ime ); /* * Check and adjust for Daylight Saving Time. */ if ( _daylight && _isindst( ptm ) ) { #ifdef _POSIX_ ltime -= _dstoffset - _timezone; #else ltime += 3600L; #endif ptm = gmtime( (time_t *)<ime ); ptm->tm_isdst = 1; } } else { ptm = gmtime( ptime ); /* * The date falls with the first three, or last three days * of the Epoch. It is possible the time_t representation * would overflow or underflow while compensating for * timezone and Daylight Savings Time. Therefore, make the * timezone and Daylight Savings Time adjustments directly * in the tm structure. The beginning of the Epoch is * 00:00:00, 01-01-70 (UTC) and the last representable second * in theEpoch is 03:14:07, 01-19-2038 (UTC). This will be * used in the calculations below. * * First, adjust for the timezone. */ ltime = (long)ptm->tm_sec - _timezone; ptm->tm_sec = (int)(ltime % 60); if ( ptm->tm_sec < 0 ) { ptm->tm_sec += 60; ltime -= 60; } ltime = (long)ptm->tm_min + ltime/60; ptm->tm_min = (int)(ltime % 60); if ( ptm->tm_min < 0 ) { ptm->tm_min += 60; ltime -= 60; } ltime = (long)ptm->tm_hour + ltime/60; ptm->tm_hour = (int)(ltime % 24); if ( ptm->tm_hour < 0 ) { ptm->tm_hour += 24; ltime -=24; } ltime /= 24; if ( ltime > 0L ) { /* * There is no possibility of overflowing the tm_mday * and tm_yday fields since the date can be no later * than January 19. */ ptm->tm_wday = (ptm->tm_wday + ltime) % 7; ptm->tm_mday += ltime; ptm->tm_yday += ltime; } else if ( ltime < 0L ) { /* * It is possible to underflow the tm_mday and tm_yday * fields. If this happens, then adjusted date must * lie in December 1969. */ ptm->tm_wday = (ptm->tm_wday + 7 + ltime) % 7; if ( (ptm->tm_mday += ltime) <= 0 ) { ptm->tm_mday += 31; ptm->tm_yday = 365; ptm->tm_mon = 11; ptm->tm_year--; } else { ptm->tm_yday += ltime; } } #ifdef _POSIX_ /* * In Posix, it is possible either the first or last three * days of the Epoch might lie with Daylight Savings Time in * certain time zones. */ if ( _isindst(ptm) ) { ltime = (long)ptm->tm_sec + _dstoffset; ptm->tm_sec = (int)(ltime % 60); if ( ptm->tm_sec < 0 ) { ptm->tm_sec += 60; ltime -= 60; } ltime = (long)ptm->tm_min + ltime/60; ptm->tm_min = (int)(ltime % 60); if ( ptm->tm_min < 0 ) { ptm->tm_min += 60; ltime -= 60; } ltime = (long)ptm->tm_hour + ltime/60; ptm->tm_hour = (int)(ltime % 24); if ( ptm->tm_hour < 0 ) { ptm->tm_hour += 24; ltime -=24; } ltime /= 24; if ( ltime > 0L ) { /* * There is no possibility of overflowing the * tm_mday and tm_yday fields since the date * can be no later than January 19. */ ptm->tm_wday = (ptm->tm_wday + ltime) % 7; ptm->tm_mday += ltime; ptm->tm_yday += ltime; } else if ( ltime < 0L ) { /* * It is possible to underflow the tm_mday * and tm_yday fields. If this happens, then * adjusted date must lie in December 1969. */ ptm->tm_wday = (ptm->tm_wday + 7 + ltime) % 7; if ( (ptm->tm_mday += ltime) <= 0 ) { ptm->tm_mday += 31; ptm->tm_yday = 365; ptm->tm_mon = 12; ptm->tm_year--; } else { ptm->tm_yday += ltime; } } } #endif } return(ptm); }