c-decl.c: Add warn_multichar.

* c-decl.c: Add warn_multichar.
        (c_decode_option): Handle -Wno-multichar.
        * c-lex.c (yylex): Check it.
        * c-tree.h: Declare it.
        * toplev.c (lang_options): Add it.
        * invoke.texi: Document it.

From-SVN: r20968

gcc/ChangeLog

@@ -1,3 +1,12 @@
+Mon Jul  6 22:50:48 1998  Jason Merrill  <jason@yorick.cygnus.com>
+
+	* c-decl.c: Add warn_multichar.
+	(c_decode_option): Handle -Wno-multichar.
+	* c-lex.c (yylex): Check it.
+	* c-tree.h: Declare it.
+	* toplev.c (lang_options): Add it.
+	* invoke.texi: Document it.
+
 Mon Jul  6 22:47:55 1998  J"orn Rennecke <amylaar@cygnus.co.uk>
 
 	* gcse.c (hash_scan_insn): New argument IN_LIBCALL_BLOCK.  Changed

gcc/c-decl.c

@@ -577,6 +577,10 @@ int warn_unknown_pragmas = 0; /* Tri state variable.  */
 
 int warn_sign_compare = -1;
 
+/* Nonzero means warn about use of multicharacter literals.  */
+
+int warn_multichar = 1;
+
 /* Nonzero means `$' can be in an identifier.  */
 
 #ifndef DOLLARS_IN_IDENTIFIERS
@@ -792,6 +796,10 @@ c_decode_option (argc, argv)
     warn_sign_compare = 1;
   else if (!strcmp (p, "-Wno-sign-compare"))
     warn_sign_compare = 0;
+  else if (!strcmp (p, "-Wmultichar"))
+    warn_multichar = 1;
+  else if (!strcmp (p, "-Wno-multichar"))
+    warn_multichar = 0;
   else if (!strcmp (p, "-Wunknown-pragmas"))
     /* Set to greater than 1, so that even unknown pragmas in system
        headers will be warned about.  */

gcc/c-lex.c

@@ -1872,7 +1872,7 @@ yylex ()
 	    num_chars = max_chars;
 	    error ("character constant too long");
 	  }
-	else if (num_chars != 1 && ! flag_traditional)
+	else if (num_chars != 1 && ! flag_traditional && warn_multichar)
 	  warning ("multi-character character constant");
 
 	/* If char type is signed, sign-extend the constant.  */

gcc/c-tree.h

@@ -505,6 +505,10 @@ extern int warn_missing_braces;
 
 extern int warn_sign_compare;
 
+/* Warn about multicharacter constants.  */
+
+extern int warn_multichar;
+
 /* Nonzero means we are reading code that came from a system header file.  */
 
 extern int system_header_p;

gcc/invoke.texi

@@ -122,7 +122,7 @@ in the following sections.
 -Wimplicit-function-declaration  -Wimport
 -Werror-implicit-function-declaration  -Winline
 -Wlarger-than-@var{len}  -Wmain  -Wmissing-declarations
--Wmissing-prototypes  -Wnested-externs  -Wno-import  
+-Wmissing-prototypes  -Wmultichar  -Wnested-externs  -Wno-import  
 -Wold-style-cast  -Woverloaded-virtual  -Wparentheses
 -Wpointer-arith  -Wredundant-decls  -Wreorder  -Wreturn-type
 -Wshadow  -Wsign-compare  -Wstrict-prototypes  -Wswitch
@@ -1287,6 +1287,11 @@ Same as @samp{-Wimplicit-int} and @samp{-Wimplicit-function-}@*
 Warn if the type of @samp{main} is suspicious.  @samp{main} should be a
 function with external linkage, returning int, taking either zero
 arguments, two, or three arguments of appropriate types.
+
+@item -Wmultichar
+Warn if a multicharacter constant (@samp{'FOOF'}) is used.  Usually they
+indicate a typo in the user's code, as they have implementation-defined
+values, and should not be used in portable code.
   
 @item -Wparentheses
 Warn if parentheses are omitted in certain contexts, such

gcc/toplev.c

@@ -872,6 +872,8 @@ char *lang_options[] =
   "-Wno-missing-declarations",
   "-Wmissing-prototypes",
   "-Wno-missing-prototypes",
+  "-Wmultichar",
+  "-Wno-multichar",
   "-Wnested-externs",
   "-Wno-nested-externs",
   "-Wparentheses",