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Add DST ambiguity note to TzSpecificLocalTimeToSystemTime(Ex) documentation #2065

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Add DST ambiguity note to TzSpecificLocalTimeToSystemTime(Ex) documentation #2065

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e2cad12
Add DST ambiguity note to TzSpecificLocalTimeToSystemTime documentation
rkg96 Aug 4, 2025
98eb1ed
Update TzSpecificLocalTimeToSystemTimeEx to add same updated remarks …
rkg96 Aug 4, 2025
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9 changes: 8 additions & 1 deletion sdk-api-src/content/timezoneapi/nf-timezoneapi-tzspecificlocaltimetosystemtime.md
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Expand Up @@ -88,6 +88,13 @@ If the function fails, the return value is zero. To get extended error informati

<b>TzSpecificLocalTimeToSystemTime</b> takes into account whether daylight saving time (DST) is in effect for the local time to be converted.

> [!IMPORTANT]
> Certain local times near DST transitions may be <b>ambiguous</b> or <b>invalid</b>. Specifying such a time can result in unexpected behavior as there is no guaranteed "correct" result.
> - During the transition from daylight time to standard time, the local clock repeats. A local time within the repeated window is ambiguous because it occurs twice, once in daylight time and once in standard time.
> - During the transition from standard time to daylight time, the local clock jumps forward. A local time within the skipped window does not have a valid UTC conversion.
>
> Applications requiring continuity or precision should avoid relying on this function and look to use UTC time directly instead.

## -see-also

<a href="/windows/desktop/api/sysinfoapi/nf-sysinfoapi-getsystemtime">GetSystemTime</a>
Expand All @@ -114,4 +121,4 @@ If the function fails, the return value is zero. To get extended error informati



<a href="/windows/desktop/SysInfo/time-functions">Time Functions</a>
<a href="/windows/desktop/SysInfo/time-functions">Time Functions</a>
13 changes: 12 additions & 1 deletion ...api-src/content/timezoneapi/nf-timezoneapi-tzspecificlocaltimetosystemtimeex.md
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Expand Up @@ -74,4 +74,15 @@ A pointer to a
## -returns

If the function fails, the return value is zero. To get extended error information, call
<a href="/windows/desktop/api/errhandlingapi/nf-errhandlingapi-getlasterror">GetLastError</a>.
<a href="/windows/desktop/api/errhandlingapi/nf-errhandlingapi-getlasterror">GetLastError</a>.

## -remarks

<b>TzSpecificLocalTimeToSystemTimeEx</b> takes into account whether daylight saving time (DST) is in effect for the local time to be converted.

> [!IMPORTANT]
> Certain local times near DST transitions may be <b>ambiguous</b> or <b>invalid</b>. Specifying such a time can result in unexpected behavior as there is no guaranteed "correct" result.
> - During the transition from daylight time to standard time, the local clock repeats. A local time within the repeated window is ambiguous because it occurs twice, once in daylight time and once in standard time.
> - During the transition from standard time to daylight time, the local clock jumps forward. A local time within the skipped window does not have a valid UTC conversion.
>
> Applications requiring continuity or precision should avoid relying on this function and look to use UTC time directly instead.