[boost] boost::gregorian::date_period,how to increment/decrement the period

From: george (george13p_at_[hidden])
Date: 2006-03-26 14:19:44

hello!

boost::gregorian::days size(1);

boost::gregorian::date_period tmp(period.begin()+=size,period.end()-=size);

period=tmp;

is there any better way to increment/decrement the period object

I want 
period.begin+=size;
period.end()-=size

to be permanent to period but it doesn't,it returns an object...

any idea??

thanks for any help.