问题
I have a FILE *, returned by a call to fopen(). I need to get a file descriptor from it, to make calls like fsync(fd) on it. What's the function to get a file descriptor from a file pointer?
回答1:
The proper function is int fileno(FILE *stream). It can be found in <stdio.h>, and is a POSIX standard but not standard C.
回答2:
Even if fileno(FILE *) may return a file descriptor, be VERY careful not to bypass stdio's buffer. If there is buffer data (either read or unflushed write), reads/writes from the file descriptor might give you unexpected results.
To answer one of the side questions, to convert a file descriptor to a FILE pointer, use fdopen(3)
来源：https://stackoverflow.com/questions/3167298/how-can-i-convert-a-file-pointer-file-fp-to-a-file-descriptor-int-fd