/*
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */

/*
FUNCTION
<<fflush>>---flush buffered file output

INDEX
	fflush

ANSI_SYNOPSIS
	#include <stdio.h>
	int fflush(FILE *<[fp]>);

TRAD_SYNOPSIS
	#include <stdio.h>
	int fflush(<[fp]>)
	FILE *<[fp]>;

DESCRIPTION
The <<stdio>> output functions can buffer output before delivering it
to the host system, in order to minimize the overhead of system calls.

Use <<fflush>> to deliver any such pending output (for the file
or stream identified by <[fp]>) to the host system.

If <[fp]> is <<NULL>>, <<fflush>> delivers pending output from all
open files.

RETURNS
<<fflush>> returns <<0>> unless it encounters a write error; in that
situation, it returns <<EOF>>.

PORTABILITY
ANSI C requires <<fflush>>.

No supporting OS subroutines are required.
*/

#include <_ansi.h>
#include <stdio.h>
#include "local.h"

/* Flush a single file, or (if fp is NULL) all files.  */

int
_DEFUN(fflush, (fp),
       register FILE * fp)
{
  register unsigned char *p;
  register int n, t;

  if (fp == NULL)
    return _fwalk (_GLOBAL_REENT, fflush);

  CHECK_INIT (_REENT, fp);

  _flockfile (fp);

  t = fp->_flags;
  if ((t & __SWR) == 0)
    {
      /* For a read stream, an fflush causes the next seek to be
         unoptimized (i.e. forces a system-level seek).  This conforms
         to the POSIX and SUSv3 standards.  */
      fp->_flags |= __SNPT;
      _funlockfile (fp);
      return 0;
    }
  if ((p = fp->_bf._base) == NULL)
    {
      /* Nothing to flush.  */
      _funlockfile (fp);
      return 0;
    }
  n = fp->_p - p;		/* write this much */

  /*
   * Set these immediately to avoid problems with longjmp
   * and to allow exchange buffering (via setvbuf) in user
   * write function.
   */
  fp->_p = p;
  fp->_w = t & (__SLBF | __SNBF) ? 0 : fp->_bf._size;

  while (n > 0)
    {
      t = (*fp->_write) (fp->_cookie, (char *) p, n);
      if (t <= 0)
	{
          fp->_flags |= __SERR;
          _funlockfile (fp);
          return EOF;
	}
      p += t;
      n -= t;
    }
  _funlockfile (fp);
  return 0;
}