tzname2

tzname2 is a term used in some software libraries to refer to an additional time zone name string that sits beyond the standard tzname array defined by POSIX time.h. It is not part of the POSIX standard, and its presence, semantics, and naming vary between implementations. As a result, tzname2 is not portable across platforms and should not be relied upon for cross‑platform code.

In typical C or C++ time handling, the standard tzname variable is an array of two strings representing the standard time and daylight saving time abbreviations for the current locale. Some libraries or applications extend this concept with tzname2 to store a secondary display name, a long form of the zone name, an alias, or a locale-specific label. When tzname2 appears, its exact contents and purpose are determined by the library, not by the C or POSIX specifications.

Usage considerations include portability and compatibility. Since tzname2 is nonstandard, code that uses it may fail to compile or run on platforms that do not provide it. Developers who need robust time zone information are generally advised to rely on the IANA time zone database (zone IDs like America/New_York) and formatting APIs, rather than nonstandard extensions such as tzname2. If tzname2 is encountered in a project, it is important to consult the specific library’s documentation to understand its intended meaning, storage, and access patterns.

See also: tzname, time.h, struct tm, IANA time zone database, time zone abbreviations.