C: close FILE* - not filedescriptor [duplicate]

Question

I wondered if it was possible to release a FILE wrapper, without closing the underlying file descriptor:

void stream_function( int fd ) {
    FILE * stream = fdopen( fd, "r");
    // Read from stream with fread / fscanf
    // then close the buffered stream object with the mythical
    // xclose( stream ) function, leaving the fd intact. 
    xclose( stream );  
}


int main( ) {
   int fd = open("filename" , flags);
   stream_function( fd );
   // Continue to use fd
   close( fd );
}

Answer 1

It's not. You can use dup2(fileno(f)) to keep a copy of the file descriptor, but fclose(f) inherently and always closes fileno(f).

In cases like yours where you're using fdopen to get the FILE * to begin with, however, you can dup2 the fd before passing it to fdopen. This protects the original fd from being closed at fclose time.