NAME
ctime ctime_r
— convert a time value to a date and time
string
SYNOPSIS
#include
<time.h>
char *ctime(const time_t *clock); [TSF] char *ctime_r(const time_t *clock, char *buf);
DESCRIPTION
For ctime (): [CX] 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 IEEE Std
1003.1-2001 (“POSIX.1”) 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))
[CX] The asctime(3),
ctime (), gmtime(3), and
localtime(3) 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
reentrant. A function that is not required to be reentrant is not required
to be thread-safe.
[TSF] 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
thread-safe version ctime_r () is not required to set
tzname.
RETURN VALUE
The ctime () function shall return the
pointer returned by asctime(3) with that broken-down time
as an argument.
[TSF] 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
No errors are defined.
EXAMPLES
None.
APPLICATION USAGE
Values for the broken-down time structure can be obtained by
calling gmtime(3) or localtime(3). The
ctime () function is included for compatibility with
older implementations, and does not support localized date and time formats.
Applications should use the strftime(3) function to
achieve maximum portability.
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
asctime(3) , clock(3) , difftime(3) , gmtime(3) , localtime(3) , mktime(3) , strftime(3) , strptime(3) , time(3) , utime(3) , the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <time.h>
CHANGE HISTORY
First released in Issue 1. Derived from Issue 1 of the SVID.
Issue 5
Normative text previously in the APPLICATION USAGE section is moved to the DESCRIPTION.
The ctime_r () function is included for alignment with the POSIX Threads Extension.
A note indicating that the ctime ()
function need not be reentrant is added to the DESCRIPTION.
Issue 6
Extensions beyond the ISO C standard are marked.
In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.
The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a static data area.
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