asctime, asctime_r, asctime_s
From cppreference.com
Defined in header <time.h>
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char* asctime ( const struct tm* time_ptr ); |
(1) | |
char* asctime_r( const struct tm* time_ptr, char* buf ); |
(2) | (since C23) |
errno_t asctime_s( char* buf, rsize_t bufsz, const struct tm* time_ptr ); |
(3) | (since C11) |
1) Converts given calendar time tm 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 from time_ptr->tm_wday, one ofMon
,Tue
,Wed
,Thu
,Fri
,Sat
,Sun
.Mmm
- three-letter English abbreviated month name from time_ptr->tm_mon, one ofJan
,Feb
,Mar
,Apr
,May
,Jun
,Jul
,Aug
,Sep
,Oct
,Nov
,Dec
.dd
- 2-digit day of the month from timeptr->tm_mday as if printed by sprintf using %2dhh
- 2-digit hour from timeptr->tm_hour as if printed by sprintf using %.2dmm
- 2-digit minute from timeptr->tm_min as if printed by sprintf using %.2dss
- 2-digit second from timeptr->tm_sec as if printed by sprintf using %.2dyyyy
- 4-digit year from timeptr->tm_year + 1900 as if printed by sprintf 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 by time_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.
2) Same as (1), except that the message is written into user-provided storage
buf
, which is guaranteed to be null-terminated. The behavior is undefined if available size of the storage beginning at
buf
is less than 26 bytes.3) Same as (1), except that the message is written into user-provided storage
buf
, which is guaranteed to be null-terminated, and the following errors are detected at runtime and call the currently installed constraint handler function:
-
buf
ortime_ptr
is a null pointer -
bufsz
is less than 26 or greater than RSIZE_MAX - not all members of *time_ptr are within their normal ranges
- the year indicated by time_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 constant 1 before including
Contents |
[edit] Parameters
time_ptr | - | pointer to a tm 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 between <code>asctime</code> and ctime, and may be overwritten on each invocation of any of those functions.
2) <code>buf</code>, which points to a null-terminated character string holding the textual representation of date and time as described above after returning.
3) zero on success, non-zero on failure, in which case buf[0] is set to zero (unless <code>buf</code> is a null pointer or <code>bufsz</code> is zero or greater than RSIZE_MAX).
[edit] Notes
<code>asctime</code> returns a pointer to static data and is not thread-safe. POSIX marks this function obsolete and recommends strftime instead. The C standard also recommends strftime instead of <code>asctime</code>, <code>asctime_r</code> and <code>asctime_s</code> because <code>strftime</code> is more flexible and locale-sensitive.
POSIX limits undefined behaviors only to when the output string would be longer than 25 characters, when <code>timeptr->tm_wday</code> or <code>timeptr->tm_mon</code> are not within the expected ranges, or when <code>timeptr->tm_year</code> exceeds INT_MAX-1990.
Some implementations handle timeptr->tm_mday==0 as meaning the last day of the preceding month.
[edit] Example
Run this code
Possible output:
Tue May 26 21:51:50 2015 Tue 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
(C23)(C11) |
converts a time_t object to a textual representation (function) |
converts a tm object to custom textual representation (function) | |
C++ documentation for asctime
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