fileno

fileno

Return File Number

Portability: POSIX.1 conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
EXAMPLE
RELATED FUNCTIONS
SEE ALSO

SYNOPSIS

#include <lcio.h>

int fileno(FILE *f);

Here is the synopsis for the POSIX implementation

#include <stdio.h>

int fileno(FILE *f);

DESCRIPTION

fileno returns the file number of the stream associated with the FILE object addressed by f . If fileno is called for a file open to an HFS file, it returns the USS file descriptor for the file. If fileno is called for a socket, it returns the simulated file-descriptor number for the socket. If fileno is called for a file that is not an USS file, it fails and returns a -1.

RETURN VALUE

fileno returns an integer file number. If f is 0 or is not associated with an open stream, the value returned by fileno is unpredictable. fileno of a stream that is not USS returns a -1.

EXAMPLE

This example illustrates truncating an HFS file accessed by standard I/O. fileno obtains the file number, and then ftruncate is called to truncate the file. fflush is called before truncation to ensure that any buffered data are flushed:

/* This example must be compiled with the posix option. */
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int stdtrunc(FILE *f, long pos) {
   int fd;
   int rc;

   /* Get POSIX file descriptor.           */
   fd = fileno(f);
   if (fd == -1) {
      fputs("Cannot truncate non-HFS file\n", stderr);
      return -1;
   }
   rc = fflush(f);
   if (rc != 0) {
      perror("fflush error");
      return -1;
   }
   /* Truncate file to requested position. */
   rc = ftruncate(fd, pos);
   if (rc == -1)
      perror("ftruncate error");
   return rc;
}

RELATED FUNCTIONS

fdopen