102 lines
3.4 KiB
Text
102 lines
3.4 KiB
Text
# fflush.m4
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# serial 20
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dnl Copyright (C) 2007-2025 Free Software Foundation, Inc.
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dnl This file is free software; the Free Software Foundation
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dnl gives unlimited permission to copy and/or distribute it,
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dnl with or without modifications, as long as this notice is preserved.
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dnl This file is offered as-is, without any warranty.
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dnl From Eric Blake
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dnl Find out how to obey POSIX semantics of fflush(stdin) discarding
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dnl unread input on seekable streams, rather than C99 undefined semantics.
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AC_DEFUN([gl_FUNC_FFLUSH],
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[
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AC_REQUIRE([gl_STDIO_H_DEFAULTS])
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gl_FUNC_FFLUSH_STDIN
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case "$gl_cv_func_fflush_stdin" in
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*yes) ;;
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*) REPLACE_FFLUSH=1 ;;
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esac
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])
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dnl Determine whether fflush works on input streams.
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dnl Sets gl_cv_func_fflush_stdin.
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AC_DEFUN([gl_FUNC_FFLUSH_STDIN],
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[
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AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
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AC_CHECK_HEADERS_ONCE([unistd.h])
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AC_CACHE_CHECK([whether fflush works on input streams],
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[gl_cv_func_fflush_stdin],
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[echo hello world > conftest.txt
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AC_RUN_IFELSE([AC_LANG_PROGRAM(
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[[
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#include <stdio.h>
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#if HAVE_UNISTD_H
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# include <unistd.h>
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#else /* on Windows with MSVC */
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# include <io.h>
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#endif
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]GL_MDA_DEFINES],
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[[FILE *f = fopen ("conftest.txt", "r");
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char buffer[10];
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int fd;
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int c;
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if (f == NULL)
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return 1;
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fd = fileno (f);
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if (fd < 0 || fread (buffer, 1, 5, f) != 5)
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{ fclose (f); return 2; }
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/* For deterministic results, ensure f read a bigger buffer. */
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if (lseek (fd, 0, SEEK_CUR) == 5)
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{ fclose (f); return 3; }
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/* POSIX requires fflush-fseek to set file offset of fd. This fails
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on BSD systems and on mingw. */
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if (fflush (f) != 0 || fseek (f, 0, SEEK_CUR) != 0)
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{ fclose (f); return 4; }
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if (lseek (fd, 0, SEEK_CUR) != 5)
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{ fclose (f); return 5; }
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/* Verify behaviour of fflush after ungetc. See
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<https://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> */
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/* Verify behaviour of fflush after a backup ungetc. This fails on
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mingw. */
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c = fgetc (f);
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ungetc (c, f);
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fflush (f);
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if (fgetc (f) != c)
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{ fclose (f); return 6; }
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/* Verify behaviour of fflush after a non-backup ungetc. This fails
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on glibc 2.8 and on BSD systems. */
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c = fgetc (f);
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ungetc ('@', f);
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fflush (f);
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if (fgetc (f) != c)
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{ fclose (f); return 7; }
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fclose (f);
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return 0;
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]])],
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[gl_cv_func_fflush_stdin=yes],
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[gl_cv_func_fflush_stdin=no],
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[case "$host_os" in
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# Guess no on NetBSD, OpenBSD, native Windows.
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netbsd* | openbsd* | mingw* | windows*)
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gl_cv_func_fflush_stdin="guessing no" ;;
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*) gl_cv_func_fflush_stdin=cross ;;
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esac
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])
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rm conftest.txt
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])
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case "$gl_cv_func_fflush_stdin" in
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*yes) gl_func_fflush_stdin=1 ;;
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*no) gl_func_fflush_stdin=0 ;;
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*) gl_func_fflush_stdin='(-1)' ;;
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esac
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AC_DEFINE_UNQUOTED([FUNC_FFLUSH_STDIN], [$gl_func_fflush_stdin],
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[Define to 1 if fflush is known to work on stdin as per POSIX.1-2008
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or later, 0 if fflush is known to not work, -1 if unknown.])
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])
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# Prerequisites of lib/fflush.c.
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AC_DEFUN([gl_PREREQ_FFLUSH], [:])
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