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Q149471: PRB: Conflicting Definitions of time_t Between Windows and Mac

Article: Q149471
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbinterop kbCRT kbVC
Last Modified: 30-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The C Run-Time (CRT), included with:
   - Microsoft Visual C++, Macintosh Cross-Development Addon, versions 2.0, 4.0 
-------------------------------------------------------------------------------


SYMPTOMS
========

Mixing calls to both the Visual C++ C Runtime Library and native Macintosh
functions that rely on time_t may yield incorrect results. Most of these
functions can be found in Time.h.

CAUSE
=====

Both sets of libraries define time_t as the number of seconds elapsed since
epoch. However, Visual C++ defines epoch as 00:00:00 January 1, 1970 (GMT) and
stores the value as a signed 32-bit long. Native Macintosh functions define
epoch as 00:00:00 January 1, 1904 (GMT) and stores the value as an unsigned
32-bit long.

RESOLUTION
==========

If the source to the call to a time function is accessible, then offset the
value by 2,082,844,800 or by the value computed from the call to the Mac API
LongDateToSeconds().

     LongDateToSeconds(
         LongDateRec   lDate  // Jan 1, 1970 00:00:00
         LongDateTime* lSecs  // time_t equivalent returned
     )

If the calling module's source is inaccessible (as in many third-party
libraries), create an ASLM (Apple Shared Library Manager) module containing the
third-party library linked with Apple's native CRT, and export functions to call
the third-party library routines. This will allow you to use both CRT time
functions without conflicts.

STATUS
======

time_t has been a standard for representing time among many platforms. However,
the epoch that this is based on has not been standardized. Apple's standard is
different from those of Microsoft and UNIX System V.

REFERENCES
==========

Books Online

Additional query words:

======================================================================
Keywords          : kbinterop kbCRT kbVC 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:
Issue type        : kbprb

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

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