Skip to content

Document IANA time zone support on Windows in FindSystemTimeZoneById #11896

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 1 commit into
base: main
Choose a base branch
from
+1 −1
Open

Document IANA time zone support on Windows in FindSystemTimeZoneById #11896

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion xml/System/TimeZoneInfo.xml
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1872,7 +1872,7 @@

The `id` parameter must correspond exactly to the time zone's identifier in length, but not in case, for a successful match to occur; that is, the comparison of `id` with time zone identifiers is case-insensitive. If you want to retrieve time zone objects based on partial matches, you can write custom procedures that work with the read-only collection of <xref:System.TimeZoneInfo> objects returned by the <xref:System.TimeZoneInfo.GetSystemTimeZones%2A> method.

On Windows systems, `FindSystemTimeZoneById` tries to match `id` to the subkey names of the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Time Zones branch of the registry. On Linux and macOS, it uses time zone information available in the [ICU Library](https://unicode-org.github.io/icu/userguide/datetime/timezone/). If the registry or the library does not have the information for the time zone you desire, you can create a particular time zone either by calling one of the overloads of the <xref:System.TimeZoneInfo.CreateCustomTimeZone%2A> method or by calling <xref:System.TimeZoneInfo.FromSerializedString%2A> to deserialize a <xref:System.TimeZoneInfo> object that represents the required time zone. However, time zones created by these method calls are not system-defined time and cannot be retrieved using the <xref:System.TimeZoneInfo.FindSystemTimeZoneById%2A> method. These custom time zones can be accessed only through the object reference returned by the <xref:System.TimeZoneInfo.CreateCustomTimeZone%2A> or <xref:System.TimeZoneInfo.FromSerializedString%2A> method call.
On Windows systems, `FindSystemTimeZoneById` tries to match `id` to the subkey names of the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Time Zones branch of the registry. Starting with .NET 6, Windows systems also support IANA time zone identifiers (such as "America/Los_Angeles" or "Pacific/Auckland"), providing cross-platform time zone resolution. On Linux and macOS, it uses time zone information available in the [ICU Library](https://unicode-org.github.io/icu/userguide/datetime/timezone/). If the registry or the library does not have the information for the time zone you desire, you can create a particular time zone either by calling one of the overloads of the <xref:System.TimeZoneInfo.CreateCustomTimeZone%2A> method or by calling <xref:System.TimeZoneInfo.FromSerializedString%2A> to deserialize a <xref:System.TimeZoneInfo> object that represents the required time zone. However, time zones created by these method calls are not system-defined time and cannot be retrieved using the <xref:System.TimeZoneInfo.FindSystemTimeZoneById%2A> method. These custom time zones can be accessed only through the object reference returned by the <xref:System.TimeZoneInfo.CreateCustomTimeZone%2A> or <xref:System.TimeZoneInfo.FromSerializedString%2A> method call.

In .NET 7 and earlier versions, this method returns a new <xref:System.TimeZoneInfo> instance for each method call. This might impact performance in applications that call the `FindSystemTimeZoneById` method repeatedly with the same identifier. (In .NET 8 and later versions, this method always returns a cached <xref:System.TimeZoneInfo> instance.)

Expand Down