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std::asctime

From cppreference.com
< cpp‎ | chrono‎ | c
 
 
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asctime
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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.

Contents

[edit] Parameters

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

[edit] 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.

[edit] 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.

[edit] Example

#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

[edit] See also

converts a time_t object to a textual representation
(function) [edit]
converts a tm object to custom textual representation
(function) [edit]
(C++11)
formats and outputs a date/time value according to the specified format
(function template) [edit]
C documentation for asctime