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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CTIME(3P) POSIX Programmer's Manual CTIME(3P)
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.
ctime, ctime_r — convert a time value to a date and time string
#include <time.h>
char *ctime(const time_t *clock);
char *ctime_r(const time_t *clock, char *buf);
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.
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.
No errors are defined.
The following sections are informative.
None.
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).
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.
These functions may be removed in a future version.
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)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 2017 CTIME(3P)
Pages that refer to this page: time.h(0p), asctime(3p), clock(3p), clock_getres(3p), difftime(3p), getdate(3p), gettimeofday(3p), gmtime(3p), localtime(3p), mktime(3p), strftime(3p), time(3p), tzset(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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