Q214661: FIX: Daylight Savings Time Bug in C Run-Time Library

Article: Q214661
Product(s): Microsoft C Compiler
Version(s): winnt:4.1,4.2,5.0,6.0
Operating System(s): 
Keyword(s): kbservicepack kbCRT kbVC500 kbVC600bug kbVS600sp2 kbVS600SP1 kbVS600sp3fixkbbuglist
Last Modified: 07-MAY-2001

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The information in this article applies to:

- Microsoft Visual C++, version 4.1 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

The C-Run-time Library date/time functions might fail to calculate the correct
time during the first week of daylight savings time beginning April 1, 2001. The
bug corrects itself after one week, on the following Sunday. This bug is not
related to the year 2000 problem.

CAUSE
=====

The bug is caused by a logic error in the C-Run-time library's cvtdate helper
function.


STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.This bug was corrected in Visual Studio 6.0 Service
Pack 3. For more information about Visual Studio service packs, please see the
following articles in the Microsoft Knowledge Base:

Q194022 INFO: Visual Studio 6.0 Service Packs, What, Where, Why

Q194295 HOWTO: Tell That Visual Studio 6.0 Service Packs Are Installed

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

The following sample program reproduces the problem:

  // ----------------- start of sample program -------------------------

  // Compiler switches needed : none.

  #include <time.h>;
  #include <stdio.h>
  #include <stdlib.h>
  #include <stdarg.h>

  int main ()
  {
      struct tm ltm;
      time_t tstamp = 0;

      ltm.tm_year = 90;	/* First valid year .*/ 
      ltm.tm_mon = 3;		/* April. */ 
      ltm.tm_mday = 1;	/* 1st of the month. */ 
      ltm.tm_hour = 3;	/* At 3:00 am. */ 
      ltm.tm_min = 0;
      ltm.tm_sec = 0;
      ltm.tm_wday =0;
      ltm.tm_yday = 0;

      while (ltm.tm_year <= 2005)
      {
          ltm.tm_isdst = -1;

  	// mktime indirectly calls cvtdate which has the logic bug.
  	tstamp = mktime(&ltm);

  	/* If it's Sunday April 1st, it should also be DST */ 
  	if (!ltm.tm_wday && !ltm.tm_isdst)
  	{
  	    printf("April 01 is the first Sunday in April, %d  \ 
              -it should be DST but tm_isdst says it's \ 
              not!\n", 1900+ltm.tm_year);
  	    while (!ltm.tm_isdst)
  	    {
  		ltm.tm_mday++;
  		ltm.tm_isdst=-1;
  		tstamp = mktime(&ltm);
  	    }
  	    printf("\tDST is reported as starting on  \ 
              %d/%d/%d\n", 1+ltm.tm_mon, ltm.tm_mday, \ 
  	    1900+ltm.tm_year);
  	
              ltm.tm_mday = 1;
  	}
  	
          ltm.tm_year++;
  	
      }

      return 0;
  }

  // ----------------- end  of sample program ---------------------------

REFERENCES
==========

http://msdn.microsoft.com/visualc/headlines/2001.asp

Additional query words: y2k year2000

======================================================================
Keywords          : kbservicepack kbCRT kbVC500 kbVC600bug kbVS600sp2 kbVS600SP1 kbVS600sp3fix kbbuglist
Technology        : kbVCsearch kbAudDeveloper kbVC410 kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : winnt:4.1,4.2,5.0,6.0
Hardware          : ALPHA x86
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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