fileno

 NAME
  fileno - return file descriptor given a file pointer

 SYNOPSIS
  #include <stdio.h>

  int fd = fileno(fp);                (MACRO)
  FILE *fp;

 FUNCTION
  The fileno() macro returns the file descriptor (open, close, read,
  write) associated with the file pointer (fopen, fclose, fread,
  fwrite).

  This is still not the AmigaDOS file handle... to get that you must
  use the fdtofh() call.

 WARNING
  If you use the file descriptor of a file pointer the file pointer
  will get its seek position confused.  Additionally, there might
  be unflushed data in the file pointer's buffers that has not
  been written out to the file descriptor yet.  There also might
  be unread input on the file pointer's input buffers already
  read from the file descriptor.

 NOTE
  refer to the file_pointer manual page for general information

 EXAMPLE
  /*
   *  stdin defaults to file descriptor 0
   *  stdout defaults to file descriptor 1
   *  stderr defaults to file descriptor 2
   */

  #include <stdio.h>
  #include <assert.h>

  main()
  {
      assert(fileno(stdin) == 0);
      assert(fileno(stdout) == 1);
      assert(fileno(stderr) == 2);
      return(0);
  }

 INPUTS
  FILE *fp;   file pointer

 RESULTS
  int fd;     associated file descriptor

 SEE ALSO
  fdopen, fopen, fclose, open, close