Difference between fflush and fsync

今天做APUE的习题，对fflush和fsync的区别不甚了解，google了一下，找到了一个回答备忘下：

原文链接：http://stackoverflow.com/questions/2340610/difference-between-fflush-and-fsync

fflush()

 works
on FILE* , it just flushes the internal buffers in the 

FILE*

 of
your application out to the OS.

fsync

 works
on a lower level, it tells the OS to flush its buffers to the physical media.

OSs heavily caches data you write to a file. If the OS enforced every write to hit the drive, things would be very slow. fsync(among other things)
allows you to control when the data should hit the drive.

Furthermore, fsync/commit works on a file descriptor. It has no knowledge of a FILE* and can't flush its buffers. FILE* lives in your application, file descriptors lives in the OS kernel, typically.

还有一个链接，写的也很详细：http://blog.chinaunix.net/uid-1911213-id-3412851.html