ctime(3p) — Linux manual page


CTIME(3P)                 POSIX Programmer's Manual                CTIME(3P)

PROLOG         top

       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.

NAME         top

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

SYNOPSIS         top

       #include <time.h>

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

DESCRIPTION         top

       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.1‐2008 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:


       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() does not set tzname, it shall not set daylight and shall
       not set timezone.

RETURN VALUE         top

       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.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top



       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

RATIONALE         top

       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


       These functions may be removed in a future version.

SEE ALSO         top

       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.1‐2008, time.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                           CTIME(3P)

Pages that refer to this page: time.h(0p)asctime(3p)asctime_r(3p)clock(3p)clock_getres(3p)clock_gettime(3p)difftime(3p)getdate(3p)gettimeofday(3p)gmtime(3p)gmtime_r(3p)localtime(3p)localtime_r(3p)mktime(3p)strftime(3p)strftime_l(3p)time(3p)tzname(3p)tzset(3p)