strftime怎么用???

strftime请各位大哥指点下~~
size_t strftime( char *str, size_t maxsize, const char *fmt, struct tm *time );
搞不懂最后一个 struct tm *time 是什么意思 ~~要怎么实现???
最好可以给小弟举例说下~~~~
感激不尽~~~