cpplib: expression parser messages

[Neil Booth <NeilB at earthling dot net>]

This simple patch just improves some error messages by mentioning the
operator the parser has stumbled on.  For example, the line

#if >= 4

used to produce the message

"operator has no left operand"

It now produces

"operator `>=' has no left operand"

By the way, Zack, in testing this I noticed that

#if #

segfaults.  This happens because an assertion of zero length gets
looked up in cpphash.c, and the hashing code assumes the length of the
identifier it's passed is at least one.  As I'm not sure whether you
want to fix the hash code or simply prevent lookup, I'll leave that to
you.

OK to commit?

Neil.

	* cppexp.c:  New typedef op_t.  struct operation and struct 
	token updated to use it.
	(op_to_str): New function.
	(_cpp_parse_expr): Error messages modified to use op_to_str.

Index: cppexp.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/cppexp.c,v
retrieving revision 1.44
diff -u -p -r1.44 cppexp.c
--- cppexp.c	2000/04/02 08:27:23	1.44
+++ cppexp.c	2000/04/02 09:15:41
@@ -73,6 +73,8 @@ Written by Per Bothner 1994.  */
    number with SUM's sign, where A, B, and SUM are all C integers.  */
 #define possible_sum_sign(a, b, sum) ((((a) ^ (b)) | ~ ((a) ^ (sum))) < 0)
 
+typedef short op_t;
+
 static void integer_overflow PARAMS ((cpp_reader *));
 static HOST_WIDEST_INT left_shift PARAMS ((cpp_reader *, HOST_WIDEST_INT,
 					   unsigned int,
@@ -88,7 +90,7 @@ static struct operation parse_defined PA
 static HOST_WIDEST_INT parse_escape PARAMS ((cpp_reader *, U_CHAR **,
 					     HOST_WIDEST_INT));
 static struct operation lex PARAMS ((cpp_reader *, int));
-
+static const char * op_to_str PARAMS ((op_t));
 
 #define ERROR 299
 #define OROR 300
@@ -106,7 +108,7 @@ static struct operation lex PARAMS ((cpp
 
 struct operation
 {
-  short op;
+  op_t op;
   U_CHAR prio;         /* Priority of op.  */
   U_CHAR flags;
   U_CHAR unsignedp;    /* True if value should be treated as unsigned.  */
@@ -378,14 +380,15 @@ parse_defined (pfile)
   op.op = ERROR;
   return op;
 }
-
 
-struct token {
+struct token
+{
   const char *operator;
-  int token;
+  op_t token;
 };
 
-static const struct token tokentab2[] = {
+static const struct token tokentab2[] =
+{
   {"&&", ANDAND},
   {"||", OROR},
   {"<<", LSH},
@@ -476,6 +479,25 @@ lex (pfile, skip_evaluation)
   }
 }
 
+/* Convert an operator ID to a string.  */
+static const char *
+op_to_str (op)
+     op_t op;
+{
+  static char str[5];
+  const struct token *toktab;
+
+  /* See if it is a special token of length 2.  */
+  for (toktab = tokentab2; toktab->operator != NULL; toktab++)
+    if (op == toktab->token)
+      return toktab->operator;
+
+  if (ISGRAPH (op))
+    sprintf (str, "%c", (int) op);
+  else
+    sprintf (str, "\\%03o", (int) op);
+  return str;
+}
 
 /* Parse a C escape sequence.  STRING_PTR points to a variable
    containing a pointer to the string to parse.  That pointer
@@ -830,7 +852,8 @@ _cpp_parse_expr (pfile)
 	      if (top->op == '(')
 		cpp_error (pfile, "void expression between '(' and ')'");
 	      else
-		cpp_error (pfile, "operator has no right operand");
+		cpp_error (pfile, "operator `%s' has no right operand",
+			   op_to_str (top->op));
 	      goto syntax_error;
 	    }
 
@@ -993,11 +1016,8 @@ _cpp_parse_expr (pfile)
 	      op.unsignedp = unsigned2;
 	      goto push_immediate;
 	    default:
-	      if (ISGRAPH (top[1].op))
-		cpp_error (pfile, "unimplemented operator '%c'", top[1].op);
-	      else
-		cpp_error (pfile, "unimplemented operator '\\%03o'",
-			   top[1].op);
+	      cpp_error (pfile, "unimplemented operator `%s'",
+			 op_to_str (top[1].op));
 	      break;
 	    case FINISHED:
 	      /* Reducing this dummy operator indicates we've finished.  */
@@ -1029,9 +1049,11 @@ _cpp_parse_expr (pfile)
       if (((flags & NO_L_OPERAND) != 0) ^ ((top->flags & HAVE_VALUE) == 0))
 	{
 	  if (flags & NO_L_OPERAND)
-	    cpp_error (pfile, "missing binary operator");
+	    cpp_error (pfile, "missing binary operator before `%s'",
+		       op_to_str (op.op));
 	  else
-	    cpp_error (pfile, "operator has no left operand");
+	    cpp_error (pfile, "operator `%s' has no left operand",
+		       op_to_str (op.op));
 	  goto syntax_error;
 	}