std::asctime

 

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Date and time library

Time point time_point (C++11) clock_time_conversion (C++20)   clock_cast (C++20) Duration duration (C++11) Clocks system_clock (C++11) steady_clock (C++11) is_clock (C++20) utc_clock (C++20) tai_clock (C++20) high_resolution_clock (C++11) gps_clock (C++20) file_clock (C++20) local_t (C++20) Time of day is_amis_pm (C++20)(C++20) make12make24 (C++20)(C++20) hh_mm_ss (C++20)

Calendar day (C++20) month (C++20) year (C++20) weekday (C++20) operator/ (C++20) year_month_day (C++20) year_month_day_last (C++20) year_month_weekday (C++20) year_month_weekday_last (C++20)   weekday_indexed (C++20) weekday_last (C++20) month_day (C++20) month_day_last (C++20) month_weekday (C++20) month_weekday_last (C++20) year_month (C++20) last_speclast (C++20)(C++20) chrono I/O parse (C++20)

Time zone tzdb (C++20) tzdb_list (C++20) get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)(C++20)(C++20)(C++20) sys_info (C++20) local_info (C++20) nonexistent_local_time (C++20) ambiguous_local_time (C++20) locate_zone (C++20) current_zone (C++20) time_zone (C++20) choose (C++20) zoned_traits (C++20) zoned_time (C++20) time_zone_link (C++20) leap_second (C++20) leap_second_info (C++20) get_leap_second_info (C++20) C-style date and time

 

C-style date and time utilities

Functions

Time manipulation

difftime

time

clock

timespec_get (C++17)

timespec_getres (C++26)

Format conversions

asctime (deprecated in C++26)

ctime (deprecated in C++26)

strftime

wcsftime

gmtime

localtime

mktime

Constants

CLOCKS_PER_SEC

Types

tm

time_t

clock_t

timespec (C++17)

 

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

See also

ctime	converts a std::time_t object to a textual representation (function)
strftime	converts a std::tm object to custom textual representation (function)
put_time (C++11)	formats and outputs a date/time value according to the specified format (function template)
C documentation for asctime