ASCTIME(P) POSIX Programmer's Manual ASCTIME(P)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.
NAME
asctime, asctime_r - convert date and time to a string
SYNOPSIS
#include <time.h>
char *asctime(const struct tm *timeptr);
char *asctime_r(const struct tm *restrict tm, char *restrict buf);
DESCRIPTION
For asctime(): 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 defers to the ISO C standard.
The asctime() function shall convert the broken-down time in the struc‐
ture pointed to by timeptr into a string in the form:
Sun Sep 16 01:03:52 1973\n\0
using the equivalent of the following algorithm:
char *asctime(const struct tm *timeptr)
{
static char wday_name[7][3] = {
"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
static char mon_name[12][3] = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun",
"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
static char result[26];
sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
wday_name[timeptr->tm_wday],
mon_name[timeptr->tm_mon],
timeptr->tm_mday, timeptr->tm_hour,
timeptr->tm_min, timeptr->tm_sec,
1900 + timeptr->tm_year);
return result;
}
The tm structure is defined in the <time.h> header.
The asctime(), ctime(), gmtime(), and localtime() functions shall
return values in one of two static objects: a broken-down time struc‐
ture and an array of type char. Execution of any of the functions may
overwrite the information returned in either of these objects by any of
the other functions.
The asctime() function need not be reentrant. A function that is not
required to be reentrant is not required to be thread-safe.
The asctime_r() function shall convert the broken-down time in the
structure pointed to by tm into a string (of the same form as that
returned by asctime()) that is placed in the user-supplied buffer
pointed to by buf (which shall contain at least 26 bytes) and then
return buf.
RETURN VALUE
Upon successful completion, asctime() shall return a pointer to the
string.
Upon successful completion, asctime_r() shall return a pointer to a
character string containing the date and time. This string is pointed
to by the argument buf. If the function is unsuccessful, it shall
return NULL.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Values for the broken-down time structure can be obtained by calling
gmtime() or localtime(). This function is included for compatibility
with older implementations, and does not support localized date and
time formats. Applications should use strftime() to achieve maximum
portability.
The asctime_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 ALSOclock() , ctime() , difftime() , gmtime() , localtime() , mktime() ,
strftime() , strptime() , time() , utime() , the Base Definitions vol‐
ume of IEEE Std 1003.1-2001, <time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE/The Open Group 2003 ASCTIME(P)
