Date/Time in C++

["Jonathon M. Merz" <merz@mscs.mu.edu>]

>
>oh! and btw.. does anyone know a good link where I can get examples of
>working with dates in C++ ? like converting from the standard format to
>"Gregorian" (and I *know* this is not even close to the English word but I
>don't how to translate it, hope you guys understand.)

First, as far as I know, "Gregorian" is the proper English term for 
it...  We do follow the Gregorian Calendar.  Of course the actual term for 
it usually just gets thrown around by historians while I doubt that most 
people usually even think about whether there even _is_ a name for our 
calendar system (I know I don't except for the good old days of school with 
history classes!)  But anyway, I digress...

I don't know of any sites for working with dates (though I'm sure they're 
out there), but here's one I've got on my computer here:


Out of the functions demonstrated in the example below, I usually find 
strftime() the most useful, so here's a quick list of the %() formatting 
operators (If you look below, it works basically like printf) that can be 
used with it:

-------------------------------
%a
Abbreviated weekday name

%A
Full weekday name

%b
Abbreviated month name

%B
Full month name

%c
Date and time representation appropriate for locale

%d
Day of month as decimal number (01 – 31)

%H
Hour in 24-hour format (00 – 23)

%I
Hour in 12-hour format (01 – 12)

%j
Day of year as decimal number (001 – 366)

%m
Month as decimal number (01 – 12)

%M
Minute as decimal number (00 – 59)

%p
Current locale’s A.M./P.M. indicator for 12-hour clock

%S
Second as decimal number (00 – 59)

%U
Week of year as decimal number, with Sunday as first day of week (00 – 53)

%w
Weekday as decimal number (0 – 6; Sunday is 0)

%W
Week of year as decimal number, with Monday as first day of week (00 – 53)

%x
Date representation for current locale

%X
Time representation for current locale

%y
Year without century, as decimal number (00 – 99)

%Y
Year with century, as decimal number

%z, %Z
Time-zone name or abbreviation; no characters if time zone is unknown

%%
Percent sign

-------------------------------


/* TIMES.C illustrates various time and date functions including:
  *      time            _ftime          ctime       asctime
  *      localtime       gmtime          mktime      _tzset
  *      _strtime        _strdate        strftime
  *
  * Also the global variable:
  *      _tzname
  */

#include <time.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/timeb.h>
#include <string.h>

void main()
{
     char tmpbuf[128], ampm[] = "AM";
     time_t ltime;
     struct _timeb tstruct;
     struct tm *today, *gmt, xmas = { 0, 0, 12, 25, 11, 93 };

     /* Set time zone from TZ environment variable. If TZ is not set,
      * the operating system is queried to obtain the default value
      * for the variable.
      */
     _tzset();

     /* Display operating system-style date and time. */
     _strtime( tmpbuf );
     printf( "OS time:\t\t\t\t%s\n", tmpbuf );
     _strdate( tmpbuf );
     printf( "OS date:\t\t\t\t%s\n", tmpbuf );

     /* Get UNIX-style time and display as number and string. */
     time( &ltime );
     printf( "Time in seconds since UTC 1/1/70:\t%ld\n", ltime );
     printf( "UNIX time and date:\t\t\t%s", ctime( &ltime ) );

     /* Display UTC. */
     gmt = gmtime( &ltime );
     printf( "Coordinated universal time:\t\t%s", asctime( gmt ) );

     /* Convert to time structure and adjust for PM if necessary. */
     today = localtime( &ltime );
     if( today->tm_hour > 12 )
     {
    strcpy( ampm, "PM" );
    today->tm_hour -= 12;
     }
     if( today->tm_hour == 0 )  /* Adjust if midnight hour. */
    today->tm_hour = 12;

     /* Note how pointer addition is used to skip the first 11
      * characters and printf is used to trim off terminating
      * characters.
      */
     printf( "12-hour time:\t\t\t\t%.8s %s\n",
        asctime( today ) + 11, ampm );

     /* Print additional time information. */
     _ftime( &tstruct );
     printf( "Plus milliseconds:\t\t\t%u\n", tstruct.millitm );
     printf( "Zone difference in seconds from UTC:\t%u\n",
              tstruct.timezone );
     printf( "Time zone name:\t\t\t\t%s\n", _tzname[0] );
     printf( "Daylight savings:\t\t\t%s\n",
              tstruct.dstflag ? "YES" : "NO" );

     /* Make time for noon on Christmas, 1993. */
     if( mktime( &xmas ) != (time_t)-1 )
    printf( "Christmas\t\t\t\t%s\n", asctime( &xmas ) );

     /* Use time structure to build a customized time string. */
     today = localtime( &ltime );

     /* Use strftime to build a customized time string. */
     strftime( tmpbuf, 128,
          "Today is %A, day %d of %B in the year %Y.\n", today );
     printf( tmpbuf );
}


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