ctime, ctime_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* ctime(consttime_t* timer);			(until C23)
[[deprecated]]char* ctime(consttime_t* timer);			(since C23)
errno_t ctime_s(charbuf, rsize_t bufsz,consttime_t timer);		(2)	(since C11)

1) Converts given time since epoch to a calendar local time and then to a textual representation, as if by callingasctime(localtime(timer)) orasctime(localtime_r(timer,&(structtm){0}))(since C23).This function is deprecated and should not be used in new code.(since C23)

2) Same as(1), except that the function is equivalent toasctime_s(buf, bufsz, localtime_s(timer,&(structtm){0})), and the following errors are detected at runtime and call the currently installedconstraint handler function:

buf ortimer is a null pointer
bufsz is less than26 or greater thanRSIZE_MAX

As with all bounds-checked functions,ctime_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>.

The resulting string has the following format:

Www Mmm dd hh:mm:ss yyyy\n

Www - the day of the week (one ofMon,Tue,Wed,Thu,Fri,Sat,Sun).
Mmm - the month (one ofJan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec).
dd - the day of the month
hh - hours
mm - minutes
ss - seconds
yyyy - years

The function does not support localization.

[edit]Parameters

timer	-	pointer to atime_t object specifying the time to print
buf	-	pointer to the first element of a char array of size at least`bufsz`
bufsz	-	max number of bytes to output, typically the size of the buffer pointed to by`buf`

[edit]Return value

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

2) zero on success (in which case the string representation of time has been written out to the array pointed to bybuf), or non-zero on failure (in which case, the terminating null character is always written tobuf[0] unlessbuf is a null pointer orbufsz is zero or greater thanRSIZE_MAX.

[edit]Notes

ctime returns a pointer to static data and is not thread-safe. In addition, it modifies the statictm object which may be shared withgmtime andlocaltime. POSIX marks this function obsolete and recommendsstrftime instead. The C standard also recommendsstrftime instead ofctime andctime_s becausestrftime is more flexible and locale-sensitive.

The behavior ofctime is undefined for the values oftime_t that result in the string longer than 25 characters (e.g. year 10000).

[edit]Example

Run this code

#define __STDC_WANT_LIB_EXT1__ 1#include <time.h>#include <stdio.h> int main(void){time_t result=time(NULL);printf("%s", ctime(&result)); #ifdef __STDC_LIB_EXT1__char str[26];    ctime_s(str,sizeof str,&result);printf("%s", str);#endif}

Possible output:

Tue May 26 21:51:03 2015Tue May 26 21:51:03 2015

[edit]References

C17 standard (ISO/IEC 9899:2018):

7.27.3.2 The ctime function (p: 287-288)

K.3.8.2.2 The ctime_s function (p: 454)

C11 standard (ISO/IEC 9899:2011):

7.27.3.2 The ctime function (p: 393)

K.3.8.2.2 The ctime_s function (p: 626)

C99 standard (ISO/IEC 9899:1999):

7.23.3.2 The ctime function (p: 342)

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

4.12.3.2 The ctime function

[edit]See also

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