When I hear someone say "a Unix timestamp is in GMT" I die a little inside. It is muddy thinking that leads to many of the problems that plague this modern world. A time_t does not have a time zone at all. It is a point in time, a scalar value. A 'struct tm' is a point in spacetime, a vector value. If you are trying to express a point in time to a human, you could do that by saying ...