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   ctime_r.3p    ( 3 )

преобразовать значение времени в строку даты и времени (convert a time value to a date and time string)

Пролог (Prolog)

This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

Имя (Name)

ctime, ctime_r — convert a time value to a date and time string

Синопсис (Synopsis)

#include <time.h>

char *ctime(const time_t *clock); char *ctime_r(const time_t *clock, char *buf);


Описание (Description)

For ctime(): The functionality described on this reference page
       is aligned with the ISO C standard. Any conflict between the
       requirements described here and the ISO C standard is
       unintentional. This volume of POSIX.1‐2017 defers to the ISO C
       standard.

The ctime() function shall convert the time pointed to by clock, representing time in seconds since the Epoch, to local time in the form of a string. It shall be equivalent to:

asctime(localtime(clock))

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 char. Execution of any of the functions may overwrite the information returned in either of these objects by any of the other functions.

The ctime() function need not be thread-safe.

The ctime_r() function shall convert the calendar time pointed to by clock to local time in exactly the same form as ctime() and put the string into the array pointed to by buf (which shall be at least 26 bytes in size) and return buf.

Unlike ctime(), the ctime_r() function is not required to set tzname. If ctime_r() sets tzname, it shall also set daylight and timezone. If ctime_r() does not set tzname, it shall not set daylight and shall not set timezone.


Возвращаемое значение (Return value)

The ctime() function shall return the pointer returned by
       asctime() with that broken-down time as an argument.

Upon successful completion, ctime_r() shall return a pointer to the string pointed to by buf. When an error is encountered, a null pointer shall be returned.


Ошибки (Error)

No errors are defined.

The following sections are informative.


Примеры (Examples)

None.

Использование в приложениях (Application usage)

These functions are included only for compatibility with older
       implementations. They have undefined behavior if the resulting
       string would be too long, so the use of these functions should be
       discouraged.  On implementations that do not detect output string
       length overflow, it is possible to overflow the output buffers in
       such a way as to cause applications to fail, or possible system
       security violations. Also, these functions do not support
       localized date and time formats. To avoid these problems,
       applications should use strftime() to generate strings from
       broken-down times.

Values for the broken-down time structure can be obtained by calling gmtime() or localtime().

The ctime_r() function is thread-safe and shall return values in a user-supplied buffer instead of possibly using a static data area that may be overwritten by each call.

Attempts to use ctime() or ctime_r() for times before the Epoch or for times beyond the year 9999 produce undefined results. Refer to asctime(3p).


Обоснование (Rationale)

The standard developers decided to mark the ctime() and ctime_r()
       functions obsolescent even though they are in the ISO C standard
       due to the possibility of buffer overflow. The ISO C standard
       also provides the strftime() function which can be used to avoid
       these problems.

Будущие направления (Future directions)

These functions may be removed in a future version.

Смотри также (See also)

asctime(3p), clock(3p), difftime(3p), gmtime(3p), localtime(3p),
       mktime(3p), strftime(3p), strptime(3p), time(3p), utime(3p)

The Base Definitions volume of POSIX.1‐2017, time.h(0p)