ctime(3) Library Functions Manual ctime(3) NOM asctime, ctime, gmtime, localtime, mktime, asctime_r, ctime_r, gmtime_r, localtime_r - Convertir des dates et des temps au format annee/mois/jour ou au format ASCII BIBLIOTHEQUE Bibliotheque C standard (libc, -lc) SYNOPSIS #include char *asctime(const struct tm *tm); char *asctime_r(const struct tm *restrict tm, char tampon[restrict 26]); char *ctime(const time_t *timep); char *ctime_r(const time_t *restrict timep, char tampon[restrict 26]); struct tm *gmtime(const time_t *timep); struct tm *gmtime_r(const time_t *restrict timep, struct tm *restrict resultat); struct tm *localtime(const time_t *timep); struct tm *localtime_r(const time_t *restrict timep, struct tm *restrict resultat); time_t mktime(struct tm *tm); Exigences de macros de test de fonctionnalites pour la glibc (consulter feature_test_macros(7)) : asctime_r(), ctime_r(), gmtime_r(), localtime_r() : _POSIX_C_SOURCE || /* glibc <= 2.19 : */ _BSD_SOURCE || _SVID_SOURCE DESCRIPTION Les fonctions ctime(), gmtime() et localtime() prennent toutes un parametre de type time_t qui represente un temps en secondes. Si l'on interprete ce parametre comme une valeur absolue, il s'agit du nombre de secondes ecoulees depuis l'epoque POSIX, 1er janvier 1970 a 00:00:00 (UTC). Les fonctions asctime() et mktime() utilisent toutes deux un parametre representant le temps dans un format humain, c'est-a-dire annee, mois, jour, etc. La representation humaine (<< broken-down time >>) est stockee dans la structure tm decrite dans tm(3type). L'appel ctime(t) est equivalent a asctime(localtime(t)). Il convertit le temps calendaire t en une chaine de caracteres, terminee par un octet NULL de la forme "Wed Jun 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. La fonction gmtime() convertit le temps calendaire timep en une representation humaine exprimee en temps universel (UTC). Elle peut renvoyer NULL quand l'annee ne tient pas dans un entier. La valeur renvoyee pointe vers une structure allouee statiquement qui sera ecrasee a chaque appel ulterieur d'une fonction de date ou de temps. La fonction reentrante gmtime_r() effectue le meme travail, mais stocke le resultat dans une structure fournie par l'utilisateur. 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. La fonction asctime() convertit une date au format humain tm en une chaine de caracteres terminee par un octet NULL dans le meme format que ctime(). La valeur renvoyee pointe sur une chaine allouee statiquement qui sera ecrasee a chaque appel d'une fonction de date et de temps. La version reentrante asctime_r() effectue le meme travail, mais stocke la chaine dans un tampon d'une longueur minimale de 26 caracteres fourni par l'utilisateur. 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). Si la representation du temps au format humain specifie ne peut pas etre convertie au format calendaire (nombre de secondes depuis l'epoque POSIX, 1er janvier 1970 a 00:00:00 (UTC)), mktime() renvoie la valeur (time_t) -1 et ne modifie pas les membres de la structure du temps au format humain. VALEUR RENVOYEE S'ils reussissent, les appels gmtime() et localtime() renvoient un pointeur sur une struct tm. S'ils reussissent, les appels gmtime_r() et localtime_r() renvoient l'adresse de la structure pointee par resultat. S'ils reussissent, les appels asctime() et ctime() renvoient un pointeur sur une chaine. S'ils reussissent, les appels asctime_r() et ctime_r() renvoient un pointeur sur la chaine pointee par tampon. S'il reussit, l'appel mktime() renvoie le temps calendaire (nombre de secondes depuis l'epoque POSIX, 1er janvier 1970 a 00:00:00 (UTC)) exprime sous la forme d'une valeur de type 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. ERREURS EOVERFLOW Le resultat ne peut pas etre represente. ATTRIBUTS Pour une explication des termes utilises dans cette section, consulter attributes(7). +---------------+--------------------------+---------------------------+ |Interface | Attribut | Valeur | +---------------+--------------------------+---------------------------+ |asctime() | Securite des threads | MT-Unsafe race:asctime | | | | locale | +---------------+--------------------------+---------------------------+ |asctime_r() | Securite des threads | MT-Safe locale | +---------------+--------------------------+---------------------------+ |ctime() | Securite des threads | MT-Unsafe race:tmbuf | | | | race:asctime env locale | +---------------+--------------------------+---------------------------+ |ctime_r(), | Securite des threads | MT-Safe env locale | |gmtime_r(), | | | |localtime_r(), | | | |mktime() | | | +---------------+--------------------------+---------------------------+ |gmtime(), | Securite des threads | MT-Unsafe race:tmbuf env | |localtime() | | locale | +---------------+--------------------------+---------------------------+ VERSIONS POSIX ne preconise pas restrict pour les parametres de ctime_r() ; cela est specifique a la glibc. Dans beaucoup d'implementations, dont la glibc, un 0 dans tm_mday est interprete comme le dernier jour du mois precedent. According to POSIX.1, localtime() is required to behave as though tzset(3) was called, while localtime_r() does not have this requirement. For portable code, tzset(3) should be called before localtime_r(). STANDARDS asctime() ctime() gmtime() localtime() mktime() C23, POSIX.1-2024. gmtime_r() localtime_r() POSIX.1-2024. asctime_r() ctime_r() None. HISTORIQUE 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 Securite des threads Les quatre fonctions asctime(), ctime(), gmtime() et localtime() renvoient un pointeur vers des donnees statiques et ne sont donc pas sures dans un contexte multithread. Les versions sures dans un contexte multithread, asctime_r(), ctime_r(), gmtime_r() et localtime_r() sont specifiees dans 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. EXEMPLES 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; } VOIR AUSSI date(1), gettimeofday(2), time(2), utime(2), clock(3), difftime(3), strftime(3), strptime(3), timegm(3), tzset(3), time(7) TRADUCTION La traduction francaise de cette page de manuel a ete creee par Christophe Blaess , Stephan Rafin , Thierry Vignaud , Francois Micaux, Alain Portal , Jean-Philippe Guerard , Jean-Luc Coulon (f5ibh) , Julien Cristau , Thomas Huriaux , Nicolas Francois , Florentin Duneau , Simon Paillard , Denis Barbier , David Prevot et Lucien Gentis Cette traduction est une documentation libre ; veuillez vous reporter a la GNU General Public License version 3 concernant les conditions de copie et de distribution. 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