freopen

 NAME
  freopen - reopen a new file using an existing file pointer,
        the existing file is closed before it is reused.

 SYNOPSIS
  #include <stdio.h>

  FILE *fp = freopen(filename, modes, ofp)
  char *filename;
  char *modes;
  FILE *ofp;

 FUNCTION
  freopen works exactly like fopen but takes an additional argument...
  A file pointer to reuse.  This file pointer, ofp, must be reference
  a valid open file.  freopen() will close out ofp then reuse the
  descriptor to open the new file, returning ofp (fp == ofp) on
  success, NULL on failure.

  If the freopen fails NULL is returned and the original file
  pointer is still closed, but not free()d so you may call
  freopen again with the same ofp, even though it has already
  been closed.

  refer to the fopen() manual page for information on the modes
  string.

  freopen is often used to change a program's stdin, stdout, or
  stderr though to be frank, using a separate file pointer is
  normally much more modular.

 WARNING
  ANSI does not specify that the ofp can be used in a second freopen
  if the first freopen using ofp fails (returns NULL).  Many
  implementations free the file pointer.  This just might be
  the proper way of doing things but I dunno.  I suggest you do
  not use DICE's feature in that respect as I might have to
  change it back to free ofp if the new file is unopenable.

 NOTE
  refer to the file_pointer manual page for general information

 EXAMPLE
  /*
   *  re-open stdin to an Amiga console device
   */

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

  main()
  {
      char buf[256];

      assert(freopen("CON:0/0/320/100/freopen-in", "r", stdin));
      assert(freopen("CON:320/0/320/100/freopen-out", "w", stdout));

      /*
       *  set to line buffered
       */
      setvbuf(stdin, NULL, _IOLBF, 0);
      setvbuf(stdout, NULL, _IOLBF, 0);

      puts("Type a line in the second window");
      gets(buf);
      fclose(stdin);
      fclose(stdout);
      fprintf(stderr, "Your line was: %sn", buf);

      return(0);
  }

 INPUTS
  char *filename;     file name to open
  char *modes;        open modes string
  FILE *ofp;      open file pointer to reuse

 RESULTS
  FILE *fp;       same as ofp if the new open worked, NULL otherwise

 SEE ALSO
  fdopen, fopen, fclose, open, close