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Timezone Data Loading

This is a proposal to support the loading of time zone data resources from individual files in ICU4C, in configurations that do not otherwise support loading data from separate files.

Please provide feedback by July 15, 2014.
Designated API Reviewer: Markus
Ticket: 10942 

The intent is to permit the updating of time zone data separately from the rest of the ICU data. When the option is enabled, ICU will check first in a separate directory for time zone related resource files; if they are not found then the normal ICU data loading conventions will be followed.

The option can be specified in two ways,
  • At build time, by defining the preprocessor variable U_TIMEZONE_FILES_DIR to be the desired absolute path.
  • At run time by setting the environment variable U_TIMEZONE_FILES_DIR. This will override any build time setting.

The option adds a directory path to be checked first when opening these four resources:

If the stand-alone file(s) are not present the standard ICU resource data loading mechanisms will be followed, including any options set by udata_setFileAccess(). Any combination of the files can be supplied; for example, zoneinfo64.res could be supplied separately, with the other three resources being taken from the default ICU data file.

Setting U_TIMEZONE_FILES_DIR overrides UCONFIG_NO_FILE_IO, but for the purposes of time zone data loading only.

Issue: No API makes testing harder. Maybe we should have an internal API to allow testing without requiring a whole separate build of ICU.