PRB: Conflicting Definitions of time_t Between Windows and Mac (149471)
The information in this article applies to:
- The C Run-Time (CRT), when used with:
- Microsoft Visual C++, Macintosh Cross-Development Addon 2.0
- Microsoft Visual C++, Macintosh Cross-Development Addon 4.0
This article was previously published under Q149471 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
| Modification Type: | Major | Last Reviewed: | 11/18/2003 |
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| Keywords: | kbCRT kbinterop kbprb KB149471 |
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