# fpurge.m4 serial 12
dnl Copyright (C) 2007, 2009-2021 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FUNC_FPURGE],
[
  AC_REQUIRE([gl_STDIO_H_DEFAULTS])
  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
  AC_CHECK_HEADERS_ONCE([stdio_ext.h])
  AC_CHECK_FUNCS_ONCE([fpurge])
  AC_CHECK_FUNCS_ONCE([__fpurge])
  AC_CHECK_DECLS([fpurge], , , [[#include <stdio.h>]])
  if test "x$ac_cv_func_fpurge" = xyes; then
    HAVE_FPURGE=1
    # Detect BSD bug.  Only cygwin 1.7 and musl are known to be immune.
    AC_CACHE_CHECK([whether fpurge works], [gl_cv_func_fpurge_works],
      [AC_RUN_IFELSE(
         [AC_LANG_PROGRAM(
            [[#include <stdio.h>
]],
            [[FILE *f = fopen ("conftest.txt", "w+");
              if (!f)
                return 1;
              if (fputc ('a', f) != 'a')
                { fclose (f); return 2; }
              rewind (f);
              if (fgetc (f) != 'a')
                { fclose (f); return 3; }
              if (fgetc (f) != EOF)
                { fclose (f); return 4; }
              if (fpurge (f) != 0)
                { fclose (f); return 5; }
              if (putc ('b', f) != 'b')
                { fclose (f); return 6; }
              if (fclose (f) != 0)
                return 7;
              if ((f = fopen ("conftest.txt", "r")) == NULL)
                return 8;
              if (fgetc (f) != 'a')
                { fclose (f); return 9; }
              if (fgetc (f) != 'b')
                { fclose (f); return 10; }
              if (fgetc (f) != EOF)
                { fclose (f); return 11; }
              if (fclose (f) != 0)
                return 12;
              if (remove ("conftest.txt") != 0)
                return 13;
              return 0;
            ]])],
         [gl_cv_func_fpurge_works=yes],
         [gl_cv_func_fpurge_works=no],
         [case "$host_os" in
                     # Guess yes on musl systems.
            *-musl*) gl_cv_func_fpurge_works="guessing yes" ;;
                     # Otherwise obey --enable-cross-guesses.
            *)       gl_cv_func_fpurge_works="$gl_cross_guess_normal" ;;
          esac
         ])
      ])
    case "$gl_cv_func_fpurge_works" in
      *yes) ;;
      *) REPLACE_FPURGE=1 ;;
    esac
  else
    HAVE_FPURGE=0
  fi
  if test "x$ac_cv_have_decl_fpurge" = xno; then
    HAVE_DECL_FPURGE=0
  fi
])
