Add explicit null checks after string conversions in the shells.

samples/shell.cc

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 81 matching lines @@
       }
       if (!ExecuteString(source, file_name, false, true))
         return 1;
     }
   }
   if (run_shell) RunShell(context);
   return 0;
 }
 
 
+// Extracts a C string from a V8 Utf8Value.
+const char* ToCString(const v8::String::Utf8Value& value) {
+  return *value ? *value : "<string conversion failed>";
+}
+
+
 // The callback that is invoked by v8 whenever the JavaScript 'print'
 // function is called.  Prints its arguments on stdout separated by
 // spaces and ending with a newline.
 v8::Handle<v8::Value> Print(const v8::Arguments& args) {
   bool first = true;
   for (int i = 0; i < args.Length(); i++) {
     v8::HandleScope handle_scope;
     if (first) {
       first = false;
     } else {
       printf(" ");
     }
     v8::String::Utf8Value str(args[i]);
-    printf("%s", *str);
+    const char* cstr = ToCString(str);
+    printf("%s", cstr);
   }
   printf("\n");
   return v8::Undefined();
 }
 
 
 // The callback that is invoked by v8 whenever the JavaScript 'load'
 // function is called.  Loads, compiles and executes its argument
 // JavaScript file.
 v8::Handle<v8::Value> Load(const v8::Arguments& args) {
   for (int i = 0; i < args.Length(); i++) {
     v8::HandleScope handle_scope;
     v8::String::Utf8Value file(args[i]);
+    if (*file == NULL) {
+      return v8::ThrowException(v8::String::New("Error loading file"));
+    }
     v8::Handle<v8::String> source = ReadFile(*file);
     if (source.IsEmpty()) {
       return v8::ThrowException(v8::String::New("Error loading file"));
     }
     if (!ExecuteString(source, v8::String::New(*file), false, false)) {
       return v8::ThrowException(v8::String::New("Error executing  file"));
     }
   }
   return v8::Undefined();
 }
@@ skipping 74 matching lines @@
     if (result.IsEmpty()) {
       // Print errors that happened during execution.
       if (report_exceptions)
         ReportException(&try_catch);
       return false;
     } else {
       if (print_result && !result->IsUndefined()) {
         // If all went well and the result wasn't undefined then print
         // the returned value.
         v8::String::Utf8Value str(result);
-        printf("%s\n", *str);
+        const char* cstr = ToCString(str);
+        printf("%s\n", cstr);
       }
       return true;
     }
   }
 }
 
 
 void ReportException(v8::TryCatch* try_catch) {
   v8::HandleScope handle_scope;
   v8::String::Utf8Value exception(try_catch->Exception());
+  const char* exception_string = ToCString(exception);
   v8::Handle<v8::Message> message = try_catch->Message();
   if (message.IsEmpty()) {
     // V8 didn't provide any extra information about this error; just
     // print the exception.
-    printf("%s\n", *exception);
+    printf("%s\n", exception_string);
   } else {
     // Print (filename):(line number): (message).
     v8::String::Utf8Value filename(message->GetScriptResourceName());
+    const char* filename_string = ToCString(filename);
     int linenum = message->GetLineNumber();
-    printf("%s:%i: %s\n", *filename, linenum, *exception);
+    printf("%s:%i: %s\n", filename_string, linenum, exception_string);
     // Print line of source code.
     v8::String::Utf8Value sourceline(message->GetSourceLine());
-    printf("%s\n", *sourceline);
+    const char* sourceline_string = ToCString(sourceline);
+    printf("%s\n", sourceline_string);
     // Print wavy underline (GetUnderline is deprecated).
     int start = message->GetStartColumn();
     for (int i = 0; i < start; i++) {
       printf(" ");
     }
     int end = message->GetEndColumn();
     for (int i = start; i < end; i++) {
       printf("^");
     }
     printf("\n");
   }
 }