The number of seconds by which the local time zone is earlier than UTC
#include <time.h> long int timezone;
This global variable holds the number of seconds by which the local time zone is earlier than Coordinated Universal Time (UTC) (formerly known as Greenwich Mean Time). Whenever you call a time function, tzset() is called to set the variable, based on the current time zone.
POSIX 1003.1 XSI
daylight, tzname, tzset()
“Setting the time zone” in the Configuring Your Environment chapter of the Neutrino User's Guide