PRB: Conflicting Definitions of time_t Between Windows and Mac

 Last reviewed: July 25, 1997
Article ID: Q149471
The information in this article applies to:
  • The C Run-time (CRT) included with: - Microsoft Visual C++, Macintosh Cross-Development, 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 

Keywords          : CRTIss MacPrgIss kbinterop
Version           : 2.0 4.0
Platform          : MACINTOSH NT WINDOWS
Issue type        : kbprb
Solution Type     : Info_Provided

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Last reviewed: July 25, 1997
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