调整本地时间C ++的夏令时

I have a piece of optimized function to get the GMT time. I would like to convert it to local time. I would want to call localtime and gmtime function only once to adjust the time to localtime as calling localtime and gmtime multiple times would defeat the purpose of using the optimized function. However, my problem is how could I adjust my localtime when there is daylight saving? Any ideas on that?I have a piece of optimized function to get the