casts in glibc <ctype.h> cause standards-conformance bug

[Paul Eggert]

The C Standard requires a diagnostic for the following program:

        #include <ctype.h>
        int
        main (void)
        {
          return isalpha ("");
        }

due to the type clash in the argument to isalpha.

However, in my Debian GNU/Linux box there is no diagnostic, and from
code inspection it appears that the problem remains in glibc 2.3.1.

Here is an untested patch for this particular problem.  I suspect that
other similar ones are lurking in other function macros that cast
their arguments.

2002-12-05  Paul Eggert  <address@hidden>

        * ctype/ctype.h (__ctype_int): New function.
        (__isctype, __isctype_l): Use it so that a diagnostic is generated
        for e.g. `isalpha ("")', as the C standard requires.
        (_tolower, _toupper): Likewise, except here it's an SVID req't.

--- ctype/ctype.h       2002-09-02 11:48:00.000000000 -0700
+++ /tmp/ctype.h        2002-12-05 15:31:09.000000000 -0800
@@ -85,8 +85,10 @@
 extern __const __int32_t **__ctype_toupper_loc (void)
      __attribute__ ((__const));
 
+static inline int __ctype_int (int __c) { return __c; }
+
 #define __isctype(c, type) \
-  ((*__ctype_b_loc ())[(int) (c)] & (unsigned short int) type)
+  ((*__ctype_b_loc ())[__ctype_int (c)] & (unsigned short int) type)
 
 #define        __isascii(c)    (((c) & ~0x7f) == 0)    /* If C is a 7 bit 
value.  */
 #define        __toascii(c)    ((c) & 0x7f)            /* Mask off high bits.  
*/
@@ -209,8 +211,8 @@
 #  define isascii(c)   __isascii (c)
 #  define toascii(c)   __toascii (c)
 
-#  define _tolower(c)  ((int) (*__ctype_tolower_loc ())[(int) (c)])
-#  define _toupper(c)  ((int) (*__ctype_toupper_loc ())[(int) (c)])
+#  define _tolower(c)  ((int) (*__ctype_tolower_loc ())[__ctype_int (c)])
+#  define _toupper(c)  ((int) (*__ctype_toupper_loc ())[__ctype_int (c)])
 # endif
 
 #endif /* Not __NO_CTYPE.  */
@@ -235,7 +237,7 @@
 /* These definitions are similar to the ones above but all functions
    take as an argument a handle for the locale which shall be used.  */
 #  define __isctype_l(c, type, locale) \
-  ((locale)->__ctype_b[(int) (c)] & (unsigned short int) type)
+  ((locale)->__ctype_b[__ctype_int (c)] & (unsigned short int) type)
 
 # define __exctype_l(name)                                                   \
   extern int name (int, __locale_t) __THROW