Nice message on fopen with missing argument.

src/V3Gate.cpp

@@ -103,7 +103,7 @@ public:
     virtual AstNUser* accept(GateGraphBaseVisitor& v, AstNUser* vup=NULL) =0;
     // Returns only the result from the LAST vertex iterated over
     AstNUser* iterateInEdges(GateGraphBaseVisitor& v, AstNUser* vup=NULL) {
-	AstNUser* retp;
+	AstNUser* retp = NULL;
 	for (V3GraphEdge* edgep = inBeginp(); edgep; edgep = edgep->inNextp()) {
 	    retp = dynamic_cast<GateEitherVertex*>(edgep->fromp())->accept(v, vup);
 	}

src/verilog.y

@@ -2184,6 +2184,7 @@ statementVerilatorPragmas<nodep>:
 
 foperator_assignment<nodep>:	// IEEE: operator_assignment (for first part of expression)
 		fexprLvalue '=' delayE expr	{ $$ = new AstAssign($2,$1,$4); }
+	|	fexprLvalue '=' yD_FOPEN '(' expr ')'		{ $$ = NULL; $3->v3error("Unsupported: $fopen with multichannel descriptor.  Add ,\"w\" as second argument to open a file descriptor."); }
 	|	fexprLvalue '=' yD_FOPEN '(' expr ',' expr ')'	{ $$ = new AstFOpen($3,$1,$5,$7); }
 	//
 	//UNSUP	~f~exprLvalue '=' delay_or_event_controlE expr { UNSUP }