NAME

std::asctime - std::asctime

Synopsis

Defined in header <ctime>
char* asctime( const std::tm* time_ptr );

Converts given calendar time std::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 of Mon, Tue, Wed, Thu, Fri, Sat, Sun.
* Mmm - three-letter English abbreviated month name from time_ptr->tm_mon, one of
Jan, 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 %2d
* hh - 2-digit hour from timeptr->tm_hour as if printed by sprintf using %.2d
* mm - 2-digit minute from timeptr->tm_min as if printed by sprintf using %.2d
* ss - 2-digit second from timeptr->tm_sec as if printed by sprintf using %.2d
* yyyy - 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.

Parameters

time_ptr - pointer to a std::tm object specifying the time to print

Return value

Pointer to a static null-terminated character string holding the textual
representation of date and time. The string may be shared between std::asctime and
std::ctime, and may be overwritten on each invocation of any of those functions.

Notes

This function returns a pointer to static data and is not thread-safe. POSIX marks
this function obsolete and recommends locale-dependent std::strftime instead. In
std::locale("C") the std::strftime format string "%c\n" will be an exact match to
std::asctime output, while in other locales the format string "%a %b %e %H:%M:%S
%Y\n" will be a potentially closer but not always exact match.

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

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

Example

// Run this code

#include <ctime>
#include <iomanip>
#include <iostream>

int main()
{
const std::time_t now = std::time(nullptr);

for (const char *localeName : {"C", "en_US.utf8", "de_DE.utf8", "ja_JP.utf8" }) {
std::cout << "locale " << localeName << ":" "\n" << std::left;
std::locale::global(std::locale(localeName));

std::cout << std::setw(40) << " asctime" << std::asctime(std::localtime(&now));

// strftime output for comparison:
char buf[64];
if (strftime(buf, sizeof buf, "%c\n", std::localtime(&now))) {
std::cout << std::setw(40) << " strftime %c" << buf;
}

if (strftime(buf, sizeof buf, "%a %b %e %H:%M:%S %Y\n", std::localtime(&now))) {
std::cout << std::setw(40) << " strftime %a %b %e %H:%M:%S %Y" << buf;
}

std::cout << '\n';
}
}

Possible output:

locale C:
asctime Wed Nov 4 00:45:01 2020
strftime %c Wed Nov 4 00:45:01 2020
strftime %a %b %e %H:%M:%S %Y Wed Nov 4 00:45:01 2020

locale en_US.utf8:
asctime Wed Nov 4 00:45:01 2020
strftime %c Wed 04 Nov 2020 12:45:01 AM UTC
strftime %a %b %e %H:%M:%S %Y Wed Nov 4 00:45:01 2020

locale de_DE.utf8:
asctime Wed Nov 4 00:45:01 2020
strftime %c Mi 04 Nov 2020 00:45:01 UTC
strftime %a %b %e %H:%M:%S %Y Mi Nov 4 00:45:01 2020

locale ja_JP.utf8:
asctime Wed Nov 4 00:45:01 2020
strftime %c 2020年11月04日 00時45分01秒
strftime %a %b %e %H:%M:%S %Y 水 11月 4 00:45:01 2020