void set_dst(int(*)(const time_t *, int32_t *))
Specify the Daylight Saving function.
The Daylight Saving function should examine its parameters to determine whether Daylight Saving is in effect, and return a value appropriate for tm_isdst.
Working examples for the USA and the EU are available..
#include <util/eu_dst.h>for the European Union, and
#include <util/usa_dst.h>for the United States
If a Daylight Saving function is not specified, the system will ignore Daylight Saving.