3 # Copyright (C) 2007-2009 Free Software Foundation, Inc.
4 # This file is free software; the Free Software Foundation
5 # gives unlimited permission to copy and/or distribute it,
6 # with or without modifications, as long as this notice is preserved.
10 dnl Find out how to obey POSIX semantics of fflush(stdin) discarding
11 dnl unread input on seekable streams, rather than C99 undefined semantics.
13 AC_DEFUN([gl_FUNC_FFLUSH],
15 AC_CACHE_CHECK([whether fflush works on input streams],
16 [gl_cv_func_fflush_stdin],
17 [echo hello world > conftest.txt
18 AC_RUN_IFELSE([AC_LANG_PROGRAM(
22 ]], [[FILE *f = fopen ("conftest.txt", "r");
29 if (fd < 0 || fread (buffer, 1, 5, f) != 5)
31 /* For deterministic results, ensure f read a bigger buffer. */
32 if (lseek (fd, 0, SEEK_CUR) == 5)
34 /* POSIX requires fflush-fseek to set file offset of fd. This fails
35 on BSD systems and on mingw. */
36 if (fflush (f) != 0 || fseek (f, 0, SEEK_CUR) != 0)
38 if (lseek (fd, 0, SEEK_CUR) != 5)
40 /* Verify behaviour of fflush after ungetc. See
41 <http://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> */
42 /* Verify behaviour of fflush after a backup ungetc. This fails on
49 /* Verify behaviour of fflush after a non-backup ungetc. This fails
50 on glibc 2.8 and on BSD systems. */
57 ]])], [gl_cv_func_fflush_stdin=yes], [gl_cv_func_fflush_stdin=no],
58 [dnl Pessimistically assume fflush is broken.
59 gl_cv_func_fflush_stdin=no])
62 if test $gl_cv_func_fflush_stdin = no; then
67 AC_DEFUN([gl_REPLACE_FFLUSH],
71 AC_REQUIRE([gl_STDIO_H_DEFAULTS])
77 # Prerequisites of lib/fflush.c.
78 AC_DEFUN([gl_PREREQ_FFLUSH],
80 AC_REQUIRE([AC_C_INLINE])