asctime, asctime_s

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Compiler support
Language
Headers
Type support
Program utilities
Variadic function support
Error handling
Dynamic memory management
Strings library
Algorithms
Numerics
Date and time utilities
Input/output support
Localization support
Concurrency support(C11)
Technical Specifications
Symbol index

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Date and time utilities

Functions
Time manipulation
difftime
time
clock
timespec_get (C11)
timespec_getres (C23)
Format conversions
asctimeasctime_s (deprecated in C23)(C11)
ctimectime_s (deprecated in C23)(C11)
strftime
wcsftime (C95)
gmtimegmtime_rgmtime_s (C23)(C11)
localtimelocaltime_rlocaltime_s (C23)(C11)
mktime
Constants
CLOCKS_PER_SEC
Types
tm
time_t
clock_t
timespec (C11)

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Defined in header`<time.h>`
	(1)
char* asctime(conststructtm* time_ptr);			(until C23)
[[deprecated]]char* asctime(conststructtm* time_ptr);			(since C23)
errno_t asctime_s(char* buf, rsize_t bufsz,conststructtm* time_ptr);		(2)	(since C11)

1) Converts given calendar timetm to a textual representation of the following fixed 25-character form:Www Mmm dd hh:mm:ss yyyy\n

Www - three-letter English abbreviated day of the week fromtime_ptr->tm_wday, one ofMon,Tue,Wed,Thu,Fri,Sat,Sun.
Mmm - three-letter English abbreviated month name fromtime_ptr->tm_mon, one ofJan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec.
dd - 2-digit day of the month fromtimeptr->tm_mday as if printed bysprintf using%2d.
hh - 2-digit hour fromtimeptr->tm_hour as if printed bysprintf using%.2d.
mm - 2-digit minute fromtimeptr->tm_min as if printed bysprintf using%.2d.
ss - 2-digit second fromtimeptr->tm_sec as if printed bysprintf using%.2d.
yyyy - 4-digit year fromtimeptr->tm_year+1900 as if printed bysprintf using%4d.

The behavior is undefined if any member of*time_ptr is outside its normal range.

The behavior is undefined if the calendar year indicated bytime_ptr->tm_year has more than 4 digits or is less than the year 1000.

The function does not support localization, and the newline character cannot be removed.

The function modifies static storage and is not thread-safe.

This function is deprecated and should not be used in new code.

(since C23)

2) Same as(1), except that the message is written into user-provided storagebuf, which is guaranteed to be null-terminated, and the following errors are detected at runtime and call the currently installedconstraint handler function:

buf ortime_ptr is a null pointer
bufsz is less than 26 or greater thanRSIZE_MAX
not all members of*time_ptr are within their normal ranges
the year indicated bytime_ptr->tm_year is less than 0 or greater than 9999.

As with all bounds-checked functions,asctime_s is only guaranteed to be available if__STDC_LIB_EXT1__ is defined by the implementation and if the user defines__STDC_WANT_LIB_EXT1__ to the integer constant1 before including<time.h>.

[edit]Parameters

time_ptr	-	pointer to atm object specifying the time to print
buf	-	pointer to a user-supplied buffer at least 26 bytes in length
bufsz	-	size of the user-supplied buffer

[edit]Return value

1) pointer to a static null-terminated character string holding the textual representation of date and time as described above. The string may be shared betweenasctime andctime, and may be overwritten on each invocation of any of those functions.

2) zero on success, non-zero on failure, in which casebuf[0] is set to zero (unlessbuf is a null pointer orbufsz is zero or greater thanRSIZE_MAX).

[edit]Notes

asctime returns a pointer to static data and is not thread-safe. POSIX marks this function obsolete and recommendsstrftime instead. The C standard also recommendsstrftime instead ofasctime andasctime_s becausestrftime is more flexible and locale-sensitive.

POSIX limits undefined behaviors only to when the output string would be longer than 25 characters, whentimeptr->tm_wday ortimeptr->tm_mon are not within the expected ranges, or whentimeptr->tm_year exceedsINT_MAX-1990.

Some implementations handletimeptr->tm_mday==0 as meaning the last day of the preceding month.

[edit]Example

Run this code

#define __STDC_WANT_LIB_EXT1__ 1#include <stdio.h>#include <time.h> int main(void){structtmtm=*localtime(&(time_t){time(NULL)});printf("%s", asctime(&tm));// note implicit trailing '\n' #ifdef __STDC_LIB_EXT1__char str[26];    asctime_s(str,sizeof str,&tm);printf("%s", str);#endif}

Possible output:

Tue May 26 21:51:50 2015Tue May 26 21:51:50 2015

[edit]References

C17 standard (ISO/IEC 9899:2018):

7.27.2.1 The asctime function (p: 287)

K.3.8.2.1 The asctime_s function (p: 453-454)

C11 standard (ISO/IEC 9899:2011):

7.27.2.1 The asctime function (p: 392-393)

K.3.8.2.1 The asctime_s function (p: 624-625)

C99 standard (ISO/IEC 9899:1999):

7.23.3.1 The asctime function (p: 341-342)

C89/C90 standard (ISO/IEC 9899:1990):

4.12.3.1 The asctime function

[edit]See also

ctimectime_s (deprecated in C23)(C11)	converts atime_t object to a textual representation (function)[edit]
strftime	converts atm object to custom textual representation (function)[edit]
C++ documentation forasctime