ctime(3) Library Functions Manual ctime(3) NAZWA asctime, ctime, gmtime, localtime, mktime, asctime_r, ctime_r, gmtime_r, localtime_r - konwertuje daty i czas do postaci czasu rozlozonego lub ASCII BIBLIOTEKA Standardowa biblioteka C (libc, -lc) SKLADNIA #include char *asctime(const struct tm *tm); char *asctime_r(const struct tm *restrict tm, char buf[restrict 26]); char *ctime(const time_t *timep); char *ctime_r(const time_t *restrict timep, char buf[restrict 26]); struct tm *gmtime(const time_t *timep); struct tm *gmtime_r(const time_t *restrict timep, struct tm *restrict result); struct tm *localtime(const time_t *timep); struct tm *localtime_r(const time_t *restrict timep, struct tm *restrict result); time_t mktime(struct tm *tm); Wymagane ustawienia makr biblioteki glibc (patrz feature_test_macros(7)): asctime_r(), ctime_r(), gmtime_r(), localtime_r(): _POSIX_C_SOURCE || /* glibc w wersji <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE OPIS Funkcje ctime(), gmtime() oraz localtime() przyjmuja argument typu time_t, reprezentujacy czas kalendarzowy. Zinterpretowany jako bezwzgledna wartosc czasu okresla liczbe sekund, jakie uplynely od poczatku epoki, to jest od 1970-01-01 00:00:00 +0000 (UTC). Funkcje asctime() oraz mktime() przyjmuja jako argument czas rozlozony, ktory jest reprezentacja podzielona na rok, miesiac, dzien itd. Czas rozlozony jest przechowywany w strukturze tm, opisanej w podreczniku tm(3type). Wywolanie ctime(t) jest rownowazne asctime(localtime(t)). Przeksztalca czas kalendarzowy t na zakonczony znakiem null lancuch o postaci "sro, sty 30 21:49:08 1993\n" The abbreviations for the days of the week are "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", and "Sat". The abbreviations for the months are "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", and "Dec". The return value points to a statically allocated string which might be overwritten by subsequent calls to any of the date and time functions. The function also sets the external variables tzname, timezone, and daylight as if it called tzset(3). The reentrant version ctime_r() does the same, but stores the string in a user-supplied buffer which should have room for at least 26 bytes. It need not set tzname, timezone, and daylight. Funkcja gmtime() przeksztalca czas kalendarzowy timep na czas rozlozony, wyrazony w Coordinated Universal Time (UTC). Moze zwrocic wartosc NULL, jesli rok nie daje sie zapisac jako liczba calkowita. Zwracany jest wskaznik do statycznej struktury, ktora to struktura moze zostac nadpisana przy kolejnym wywolaniu dowolnej funkcji daty i czasu. Funkcja gmtime_r() robi to samo, ale zapisuje dane do struktury podanej przez uzytkownika. The localtime() function converts the calendar time timep to broken-down time representation, expressed relative to the user's specified timezone. The function also sets the external variables tzname, timezone, and daylight as if it called tzset(3). The return value points to a statically allocated struct which might be overwritten by subsequent calls to any of the date and time functions. The localtime_r() function does the same, but stores the data in a user-supplied struct. It need not set tzname, timezone, and daylight. Funkcja asctime() przeksztalca czas rozlozony tm na zakonczony bajtem null lancuch tego samego formatu, co ctime(). Zwracany jest wskaznik do statycznego lancucha, ktory to lancuch moze zostac nadpisany przy kolejnym wywolaniu dowolnej funkcji daty i czasu. Funkcja asctime_r() robi to samo, ale zapisuje lancuch w podanym przez uzytkownika buforze o dlugosci co najmniej 26 bajtow. The mktime() function converts a broken-down time structure, expressed as local time, to calendar time representation. The function ignores the values supplied by the caller in the tm_wday and tm_yday fields. The value specified in the tm_isdst field informs mktime() whether or not daylight saving time (DST) is in effect for the time supplied in the tm structure: a positive value means DST is in effect; zero means that DST is not in effect; and a negative value means that mktime() should (use timezone information and system databases to) attempt to determine whether DST is in effect at the specified time. See timegm(3) for a UTC equivalent of this function. The mktime() function modifies the fields of the tm structure as follows: tm_wday and tm_yday are set to values determined from the contents of the other fields; if structure members are outside their valid interval, they will be normalized (so that, for example, 40 October is changed into 9 November); tm_isdst is set (regardless of its initial value) to a positive value or to 0, respectively, to indicate whether DST is or is not in effect at the specified time. The function also sets the external variables tzname, timezone, and daylight as if it called tzset(3). Jesli podany czas rozlozony nie moze byc reprezentowany jako czas kalendarzowy (sekundy od poczatku epoki), mktime() zwraca (time_t) -1 i nie zmienia pol w podzielonej strukturze czasu. WARTOSC ZWRACANA gmtime() oraz localtime(), gdy sie zakoncza pomyslnie, zwracaja wskaznik do struct tm. gmtime_r() oraz localtime_r(), gdy sie zakoncza pomyslnie, zwracaja adres struktury wskazywanej przez result. asctime() oraz ctime(), gdy sie zakoncza pomyslnie, zwracaja wskaznik do lancucha znakow asctime_r() oraz ctime_r(), gdy sie zakoncza pomyslnie, zwracaja wskaznik do lancucha znakow, na ktory wskazuje argument buf. mktime, gdy zakonczy sie pomyslnie, zwraca czas kalendarzowy (w sekundach od poczatku epoki [tj. 1970-01-01 00:00:00 +0000 -przyp. tlum.]), wyrazony jako wartosc typu time_t On error, mktime() returns the value (time_t) -1, and leaves the tm->tm_wday member unmodified. The remaining functions return NULL on error. On error, errno is set to indicate the error. BLEDY EOVERFLOW Wynik jest niereprezentowalny. ATRYBUTY Informacje o pojeciach uzywanych w tym rozdziale mozna znalezc w podreczniku attributes(7). +---------------+--------------------------+---------------------------+ |Interfejs | Atrybut | Wartosc | +---------------+--------------------------+---------------------------+ |asctime() | Bezpieczenstwo watkowe | MT-niebezpieczne | | | | race:asctime locale | +---------------+--------------------------+---------------------------+ |asctime_r() | Bezpieczenstwo watkowe | MT-bezpieczne locale | +---------------+--------------------------+---------------------------+ |ctime() | Bezpieczenstwo watkowe | MT-niebezpieczne | | | | race:tmbuf race:asctime | | | | env locale | +---------------+--------------------------+---------------------------+ |ctime_r(), | Bezpieczenstwo watkowe | MT-bezpieczne env locale | |gmtime_r(), | | | |localtime_r(), | | | |mktime() | | | +---------------+--------------------------+---------------------------+ |gmtime(), | Bezpieczenstwo watkowe | MT-niebezpieczne | |localtime() | | race:tmbuf env locale | +---------------+--------------------------+---------------------------+ WERSJE POSIX nie okresla parametrow ctime_r() jako restrict; jest to typowe dla glibc. Wiele implementacji, wlaczajac glibc, interpretuje 0 w tm_mday jako ostatni dzien poprzedniego miesiaca. Wedlug POSIX.1, localtime() musi sie zachowywac tak, jakby tzset(3) bylo wywolane, w przypadku zas localtime_r() nie ma takiego wymagania. W przenosnym kodzie tzset(3) powinno byc wywolanie przed localtime_r(). STANDARDY asctime() ctime() gmtime() localtime() mktime() C23, POSIX.1-2024. gmtime_r() localtime_r() POSIX.1-2024. asctime_r() ctime_r() Brak. HISTORIA gmtime() localtime() mktime() C89, POSIX.1-1988. asctime() ctime() C89, POSIX.1-1988. Marked obsolescent in C23 and in POSIX.1-2008 (recommending strftime(3)). gmtime_r() localtime_r() POSIX.1-1996. asctime_r() ctime_r() POSIX.1-1996. Marked obsolescent in POSIX.1-2008. Removed in POSIX.1-2024 (recommending strftime(3)). CAVEATS Bezpieczenstwo watkowe Nastepujace cztery funkcje acstime(), ctime(), gmtime() i localtime() zwracaja wskaznik do statycznych danych i w zwiazku z tym nie sa przystosowane do wielowatkowosci. Wielowatkowe wersje acstime_r(), ctime_r(), gmtime_r() i localtime_r() sa wymienione w SUSv2. POSIX.1 says: "The asctime(), ctime(), gmtime(), and localtime() functions shall return values in one of two static objects: a broken-down time structure and an array of type char. Execution of any of the functions that return a pointer to one of these object types may overwrite the information in any object of the same type pointed to by the value returned from any previous call to any of them." This can occur in the glibc implementation. mktime() (time_t) -1 can represent a valid time (one second before the Epoch). To determine whether mktime() failed, one must use the tm->tm_wday field. See the example program in EXAMPLES. The handling of a non-negative tm_isdst in mktime() is poorly specified, and passing a value that is incorrect for the time specified yields unspecified results. Since mktime() is one of the few functions that knows when DST is in effect, providing a correct value may be difficult. One workaround for this is to call mktime() twice, once with tm_isdst set to zero, and once with tm_isdst set to a positive value, and discarding the results from the call that changes it. If neither call changes tm_isdst then the time specified probably happens during a fall-back period where DST begins or ends, and both results are valid but represent two different times. If both calls change it, that could indicate a fall-forward transition, or some other reason why the time specified does not exist. The specification of time zones and daylight saving time are up to regional governments, change often, and may include discontinuities beyond mktime's ability to document a result. For example, a change in the timezone definition may cause a clock time to be repeated or skipped without a corresponding DST change. PRZYKLADY The program below defines a wrapper that allows detecting invalid and ambiguous times, with EINVAL and ENOTUNIQ, respectively. The following shell session shows sample runs of the program: $ TZ=UTC ./a.out 1969 12 31 23 59 59 0; -1 $ $ export TZ=Europe/Madrid; $ $ ./a.out 2147483647 2147483647 00 00 00 00 -1; a.out: mktime: Value too large for defined data type $ $ ./a.out 2024 08 23 00 17 53 -1; 1724365073 $ ./a.out 2024 08 23 00 17 53 0; a.out: my_mktime: Invalid argument 1724368673 $ ./a.out 2024 08 23 00 17 53 1; 1724365073 $ $ ./a.out 2024 02 23 00 17 53 -1; 1708643873 $ ./a.out 2024 02 23 00 17 53 0; 1708643873 $ ./a.out 2024 02 23 00 17 53 1; a.out: my_mktime: Invalid argument 1708640273 $ $ ./a.out 2023 03 26 02 17 53 -1; a.out: my_mktime: Invalid argument 1679793473 $ $ ./a.out 2023 10 29 02 17 53 -1; a.out: my_mktime: Name not unique on network 1698542273 $ ./a.out 2023 10 29 02 17 53 0; 1698542273 $ ./a.out 2023 10 29 02 17 53 1; 1698538673 $ $ ./a.out 2023 02 29 12 00 00 -1; a.out: my_mktime: Invalid argument 1677668400 Program source: mktime.c #include #include #include #include #include #include #include #define is_signed(T) ((T) -1 < 1) time_t my_mktime(struct tm *tp); int main(int argc, char *argv[]) { char **p; time_t t; struct tm tm; if (argc != 8) { fprintf(stderr, "Usage: %s yyyy mm dd HH MM SS isdst\n", argv[0]); exit(EXIT_FAILURE); } p = &argv[1]; tm.tm_year = atoi(*p++) - 1900; tm.tm_mon = atoi(*p++) - 1; tm.tm_mday = atoi(*p++); tm.tm_hour = atoi(*p++); tm.tm_min = atoi(*p++); tm.tm_sec = atoi(*p++); tm.tm_isdst = atoi(*p++); errno = 0; tm.tm_wday = -1; t = my_mktime(&tm); if (tm.tm_wday == -1) err(EXIT_FAILURE, "mktime"); if (errno == EINVAL || errno == ENOTUNIQ) warn("my_mktime"); if (is_signed(time_t)) printf("%jd\n", (intmax_t) t); else printf("%ju\n", (uintmax_t) t); exit(EXIT_SUCCESS); } time_t my_mktime(struct tm *tp) { int e, isdst; time_t t; struct tm tm; unsigned char wday[sizeof(tp->tm_wday)]; e = errno; tm = *tp; isdst = tp->tm_isdst; memcpy(wday, &tp->tm_wday, sizeof(wday)); tp->tm_wday = -1; t = mktime(tp); if (tp->tm_wday == -1) { memcpy(&tp->tm_wday, wday, sizeof(wday)); return -1; } if (isdst == -1) tm.tm_isdst = tp->tm_isdst; if ( tm.tm_sec != tp->tm_sec || tm.tm_min != tp->tm_min || tm.tm_hour != tp->tm_hour || tm.tm_mday != tp->tm_mday || tm.tm_mon != tp->tm_mon || tm.tm_year != tp->tm_year || tm.tm_isdst != tp->tm_isdst) { errno = EINVAL; return t; } if (isdst != -1) goto out; tm = *tp; tm.tm_isdst = !tm.tm_isdst; tm.tm_wday = -1; mktime(&tm); if (tm.tm_wday == -1) goto out; if (tm.tm_isdst != tp->tm_isdst) { errno = ENOTUNIQ; return t; } out: errno = e; return t; } ZOBACZ TAKZE date(1), gettimeofday(2), time(2), utime(2), clock(3), difftime(3), strftime(3), strptime(3), timegm(3), tzset(3), time(7) TLUMACZENIE Autorami polskiego tlumaczenia niniejszej strony podrecznika sa: Adam Byrtek , Andrzej Krzysztofowicz , Robert Luberda i Michal Kulach Niniejsze tlumaczenie jest wolna dokumentacja. Blizsze informacje o warunkach licencji mozna uzyskac zapoznajac sie z GNU General Public License w wersji 3 lub nowszej. Nie przyjmuje sie ZADNEJ ODPOWIEDZIALNOSCI. Bledy w tlumaczeniu strony podrecznika prosimy zglaszac na adres listy dyskusyjnej . Linux man-pages 6.12 18 lutego 2025 r. ctime(3)