using date function in unix

1. how can I determine machine time in seconds on unix O/S? (i can't use 'date +%s', it's not POSIX).
2. what functions exist for 开发者_运维知识库date and epoch time in second?
3. by using date "+%format" how can i subtract 1-2 hour from present hour?

Regards

Try the time function in time.h. For example:

time_t the_time=time(NULL);
// the_time now contains the number of seconds since the epoch

To get a time in the past, just subtract the number of seconds. Since there are 3600 seconds in an hour, to go an hour back, just subtract 3600.