| 1 | # fflush.m4 serial 18
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| 2 |
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| 3 | # Copyright (C) 2007-2022 Free Software Foundation, Inc.
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| 4 | # This file is free software; the Free Software Foundation
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| 5 | # gives unlimited permission to copy and/or distribute it,
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| 6 | # with or without modifications, as long as this notice is preserved.
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| 7 |
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| 8 | dnl From Eric Blake
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| 9 |
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| 10 | dnl Find out how to obey POSIX semantics of fflush(stdin) discarding
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| 11 | dnl unread input on seekable streams, rather than C99 undefined semantics.
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| 12 |
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| 13 | AC_DEFUN([gl_FUNC_FFLUSH],
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| 14 | [
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| 15 | AC_REQUIRE([gl_STDIO_H_DEFAULTS])
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| 16 | gl_FUNC_FFLUSH_STDIN
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| 17 | case "$gl_cv_func_fflush_stdin" in
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| 18 | *yes) ;;
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| 19 | *) REPLACE_FFLUSH=1 ;;
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| 20 | esac
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| 21 | ])
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| 22 |
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| 23 | dnl Determine whether fflush works on input streams.
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| 24 | dnl Sets gl_cv_func_fflush_stdin.
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| 25 |
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| 26 | AC_DEFUN([gl_FUNC_FFLUSH_STDIN],
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| 27 | [
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| 28 | AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
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| 29 | AC_CHECK_HEADERS_ONCE([unistd.h])
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| 30 | AC_CACHE_CHECK([whether fflush works on input streams],
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| 31 | [gl_cv_func_fflush_stdin],
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| 32 | [echo hello world > conftest.txt
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| 33 | AC_RUN_IFELSE([AC_LANG_PROGRAM(
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| 34 | [[
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| 35 | #include <stdio.h>
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| 36 | #if HAVE_UNISTD_H
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| 37 | # include <unistd.h>
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| 38 | #else /* on Windows with MSVC */
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| 39 | # include <io.h>
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| 40 | #endif
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| 41 | ]GL_MDA_DEFINES],
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| 42 | [[FILE *f = fopen ("conftest.txt", "r");
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| 43 | char buffer[10];
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| 44 | int fd;
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| 45 | int c;
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| 46 | if (f == NULL)
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| 47 | return 1;
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| 48 | fd = fileno (f);
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| 49 | if (fd < 0 || fread (buffer, 1, 5, f) != 5)
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| 50 | { fclose (f); return 2; }
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| 51 | /* For deterministic results, ensure f read a bigger buffer. */
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| 52 | if (lseek (fd, 0, SEEK_CUR) == 5)
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| 53 | { fclose (f); return 3; }
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| 54 | /* POSIX requires fflush-fseek to set file offset of fd. This fails
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| 55 | on BSD systems and on mingw. */
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| 56 | if (fflush (f) != 0 || fseek (f, 0, SEEK_CUR) != 0)
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| 57 | { fclose (f); return 4; }
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| 58 | if (lseek (fd, 0, SEEK_CUR) != 5)
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| 59 | { fclose (f); return 5; }
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| 60 | /* Verify behaviour of fflush after ungetc. See
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| 61 | <https://www.opengroup.org/austin/aardvark/latest/xshbug3.txt> */
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| 62 | /* Verify behaviour of fflush after a backup ungetc. This fails on
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| 63 | mingw. */
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| 64 | c = fgetc (f);
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| 65 | ungetc (c, f);
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| 66 | fflush (f);
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| 67 | if (fgetc (f) != c)
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| 68 | { fclose (f); return 6; }
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| 69 | /* Verify behaviour of fflush after a non-backup ungetc. This fails
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| 70 | on glibc 2.8 and on BSD systems. */
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| 71 | c = fgetc (f);
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| 72 | ungetc ('@', f);
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| 73 | fflush (f);
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| 74 | if (fgetc (f) != c)
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| 75 | { fclose (f); return 7; }
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| 76 | fclose (f);
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| 77 | return 0;
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| 78 | ]])],
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| 79 | [gl_cv_func_fflush_stdin=yes],
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| 80 | [gl_cv_func_fflush_stdin=no],
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| 81 | [case "$host_os" in
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| 82 | # Guess no on native Windows.
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| 83 | mingw*) gl_cv_func_fflush_stdin="guessing no" ;;
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| 84 | *) gl_cv_func_fflush_stdin=cross ;;
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| 85 | esac
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| 86 | ])
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| 87 | rm conftest.txt
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| 88 | ])
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| 89 | case "$gl_cv_func_fflush_stdin" in
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| 90 | *yes) gl_func_fflush_stdin=1 ;;
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| 91 | *no) gl_func_fflush_stdin=0 ;;
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| 92 | *) gl_func_fflush_stdin='(-1)' ;;
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| 93 | esac
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| 94 | AC_DEFINE_UNQUOTED([FUNC_FFLUSH_STDIN], [$gl_func_fflush_stdin],
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| 95 | [Define to 1 if fflush is known to work on stdin as per POSIX.1-2008,
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| 96 | 0 if fflush is known to not work, -1 if unknown.])
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| 97 | ])
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| 98 |
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| 99 | # Prerequisites of lib/fflush.c.
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| 100 | AC_DEFUN([gl_PREREQ_FFLUSH], [:])
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