#serial 1

dnl Just like AC_C_CONST from autoconf-2.12, but with an initializer
dnl for `charset x' and with
dnl   AC_DEFINE(const, )
dnl changed to
dnl   AC_DEFINE_UNQUOTED(const, [/* empty */])
dnl to avoid this warning:
dnl   [...]/m4: Warning: Excess arguments to built-in `define' ignored

undefine([AC_C_CONST])
AC_DEFUN(AC_C_CONST,
[dnl This message is consistent in form with the other checking messages,
dnl and with the result message.
AC_CACHE_CHECK([for working const], ac_cv_c_const,
[AC_TRY_COMPILE(,
changequote(<<, >>)dnl
<<
/* Ultrix mips cc rejects this.  */
typedef int charset[2]; const charset x = {0, 0};
/* SunOS 4.1.1 cc rejects this.  */
char const *const *ccp;
char **p;
/* NEC SVR4.0.2 mips cc rejects this.  */
struct point {int x, y;};
static struct point const zero = {0,0};
/* AIX XL C 1.02.0.0 rejects this.
   It does not let you subtract one const X* pointer from another in an arm
   of an if-expression whose if-part is not a constant expression */
const char *g = "string";
ccp = &g + (g ? g-g : 0);
/* HPUX 7.0 cc rejects these. */
++ccp;
p = (char**) ccp;
ccp = (char const *const *) p;
{ /* SCO 3.2v4 cc rejects this.  */
  char *t;
  char const *s = 0 ? (char *) 0 : (char const *) 0;

  *t++ = 0;
}
{ /* Someone thinks the Sun supposedly-ANSI compiler will reject this.  */
  int x[] = {25, 17};
  const int *foo = &x[0];
  ++foo;
}
{ /* Sun SC1.0 ANSI compiler rejects this -- but not the above. */
  typedef const int *iptr;
  iptr p = 0;
  ++p;
}
{ /* AIX XL C 1.02.0.0 rejects this saying
     "k.c", line 2.27: 1506-025 (S) Operand must be a modifiable lvalue. */
  struct s { int j; const int *ap[3]; };
  struct s *b; b->j = 5;
}
{ /* ULTRIX-32 V3.1 (Rev 9) vcc rejects this */
  const int foo = 10;
}
>>,
changequote([, ])dnl
ac_cv_c_const=yes, ac_cv_c_const=no)])
if test $ac_cv_c_const = no; then
  AC_DEFINE_UNQUOTED(const, [/* empty */])
fi
])