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-rw-r--r--m4/fflush.m4100
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diff --git a/m4/fflush.m4 b/m4/fflush.m4
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+# fflush.m4 serial 18
+
+# Copyright (C) 2007-2022 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_REQUIRE([gl_STDIO_H_DEFAULTS])
+ gl_FUNC_FFLUSH_STDIN
+ case "$gl_cv_func_fflush_stdin" in
+ *yes) ;;
+ *) REPLACE_FFLUSH=1 ;;
+ esac
+])
+
+dnl Determine whether fflush works on input streams.
+dnl Sets gl_cv_func_fflush_stdin.
+
+AC_DEFUN([gl_FUNC_FFLUSH_STDIN],
+[
+ AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+ AC_CHECK_HEADERS_ONCE([unistd.h])
+ AC_CACHE_CHECK([whether fflush works on input streams],
+ [gl_cv_func_fflush_stdin],
+ [echo hello world > conftest.txt
+ AC_RUN_IFELSE([AC_LANG_PROGRAM(
+ [[
+#include <stdio.h>
+#if HAVE_UNISTD_H
+# include <unistd.h>
+#else /* on Windows with MSVC */
+# include <io.h>
+#endif
+ ]GL_MDA_DEFINES],
+ [[FILE *f = fopen ("conftest.txt", "r");
+ char buffer[10];
+ int fd;
+ int c;
+ if (f == NULL)
+ return 1;
+ fd = fileno (f);
+ if (fd < 0 || fread (buffer, 1, 5, f) != 5)
+ { fclose (f); return 2; }
+ /* For deterministic results, ensure f read a bigger buffer. */
+ if (lseek (fd, 0, SEEK_CUR) == 5)
+ { fclose (f); return 3; }
+ /* POSIX requires fflush-fseek to set file offset of fd. This fails
+ on BSD systems and on mingw. */
+ if (fflush (f) != 0 || fseek (f, 0, SEEK_CUR) != 0)
+ { fclose (f); return 4; }
+ if (lseek (fd, 0, SEEK_CUR) != 5)
+ { fclose (f); return 5; }
+ /* Verify behaviour of fflush after ungetc. See
+ <https://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> */
+ /* Verify behaviour of fflush after a backup ungetc. This fails on
+ mingw. */
+ c = fgetc (f);
+ ungetc (c, f);
+ fflush (f);
+ if (fgetc (f) != c)
+ { fclose (f); return 6; }
+ /* Verify behaviour of fflush after a non-backup ungetc. This fails
+ on glibc 2.8 and on BSD systems. */
+ c = fgetc (f);
+ ungetc ('@', f);
+ fflush (f);
+ if (fgetc (f) != c)
+ { fclose (f); return 7; }
+ fclose (f);
+ return 0;
+ ]])],
+ [gl_cv_func_fflush_stdin=yes],
+ [gl_cv_func_fflush_stdin=no],
+ [case "$host_os" in
+ # Guess no on native Windows.
+ mingw*) gl_cv_func_fflush_stdin="guessing no" ;;
+ *) gl_cv_func_fflush_stdin=cross ;;
+ esac
+ ])
+ rm conftest.txt
+ ])
+ case "$gl_cv_func_fflush_stdin" in
+ *yes) gl_func_fflush_stdin=1 ;;
+ *no) gl_func_fflush_stdin=0 ;;
+ *) gl_func_fflush_stdin='(-1)' ;;
+ esac
+ AC_DEFINE_UNQUOTED([FUNC_FFLUSH_STDIN], [$gl_func_fflush_stdin],
+ [Define to 1 if fflush is known to work on stdin as per POSIX.1-2008,
+ 0 if fflush is known to not work, -1 if unknown.])
+])
+
+# Prerequisites of lib/fflush.c.
+AC_DEFUN([gl_PREREQ_FFLUSH], [:])