# fflush.m4 serial 7

# Copyright (C) 2007-2009 Free Software Foundation, Inc.
# This file is free software; the Free Software Foundation
# gives unlimited permission to copy and/or distribute it,
# with or without modifications, as long as this notice is preserved.

dnl From Eric Blake

dnl Find out how to obey POSIX semantics of fflush(stdin) discarding
dnl unread input on seekable streams, rather than C99 undefined semantics.

AC_DEFUN([gl_FUNC_FFLUSH],
[
  AC_CACHE_CHECK([whether fflush works on input streams],
    [gl_cv_func_fflush_stdin],
    [echo hello world > conftest.txt
     AC_RUN_IFELSE([AC_LANG_PROGRAM(
       [[
#include <stdio.h>
#include <unistd.h>
       ]], [[FILE *f = fopen ("conftest.txt", "r");
	 char buffer[10];
	 int fd;
	 int c;
	 if (f == NULL)
	   return 1;
	 fd = fileno (f);
	 if (fd < 0 || fread (buffer, 1, 5, f) != 5)
	   return 2;
	 /* For deterministic results, ensure f read a bigger buffer.  */
	 if (lseek (fd, 0, SEEK_CUR) == 5)
	   return 3;
	 /* POSIX requires fflush-fseek to set file offset of fd.  This fails
	    on BSD systems and on mingw.  */
	 if (fflush (f) != 0 || fseek (f, 0, SEEK_CUR) != 0)
	   return 4;
	 if (lseek (fd, 0, SEEK_CUR) != 5)
	   return 5;
	 /* Verify behaviour of fflush after ungetc. See
	    <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt>  */
	 /* Verify behaviour of fflush after a backup ungetc.  This fails on
	    mingw.  */
	 c = fgetc (f);
	 ungetc (c, f);
	 fflush (f);
	 if (fgetc (f) != c)
	   return 6;
	 /* Verify behaviour of fflush after a non-backup ungetc.  This fails
	    on glibc 2.8 and on BSD systems.  */
	 c = fgetc (f);
	 ungetc ('@', f);
	 fflush (f);
	 if (fgetc (f) != c)
	   return 7;
	 return 0;
       ]])], [gl_cv_func_fflush_stdin=yes], [gl_cv_func_fflush_stdin=no],
     [dnl Pessimistically assume fflush is broken.
      gl_cv_func_fflush_stdin=no])
     rm conftest.txt
    ])
  if test $gl_cv_func_fflush_stdin = no; then
    gl_REPLACE_FFLUSH
  fi
])

AC_DEFUN([gl_REPLACE_FFLUSH],
[
  AC_LIBOBJ([fflush])
  AC_LIBOBJ([fseeko])
  AC_REQUIRE([gl_STDIO_H_DEFAULTS])
  REPLACE_FFLUSH=1
  REPLACE_FSEEKO=1
  gl_PREREQ_FFLUSH
])

# Prerequisites of lib/fflush.c.
AC_DEFUN([gl_PREREQ_FFLUSH],
[
  AC_REQUIRE([AC_C_INLINE])
  :
])