Fixed compiler warnings for cast to bool in generated code.

Change-Id: I7727aeb478feb23d8ef66fd1ba9499b142b3ea7d
Tested: on Linux.

src/idl_gen_cpp.cpp

@@ -234,11 +234,16 @@ static void GenEnum(const Parser &parser, EnumDef &enum_def,
 // underlying type to the interface type.
 std::string GenUnderlyingCast(const Parser &parser, const FieldDef &field,
                               bool from, const std::string &val) {
-  return (field.value.type.enum_def && IsScalar(field.value.type.base_type)) ||
-         field.value.type.base_type == BASE_TYPE_BOOL
-      ? "static_cast<" + GenTypeBasic(parser, field.value.type, from) + ">(" +
-        val + ")"
-      : val;
+  if (from && field.value.type.base_type == BASE_TYPE_BOOL) {
+    return val + " != 0";
+  } else if ((field.value.type.enum_def &&
+              IsScalar(field.value.type.base_type)) ||
+             field.value.type.base_type == BASE_TYPE_BOOL) {
+    return "static_cast<" + GenTypeBasic(parser, field.value.type, from) +
+           ">(" + val + ")";
+  } else {
+    return val;
+  }
 }
 
 std::string GenFieldOffsetName(const FieldDef &field) {

tests/monster_test_generated.h

@@ -236,7 +236,7 @@ struct Monster FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
   const MyGame::Example::Monster *testnestedflatbuffer_nested_root() const { return flatbuffers::GetRoot<MyGame::Example::Monster>(testnestedflatbuffer()->Data()); }
   const Stat *testempty() const { return GetPointer<const Stat *>(VT_TESTEMPTY); }
   Stat *mutable_testempty() { return GetPointer<Stat *>(VT_TESTEMPTY); }
-  bool testbool() const { return static_cast<bool>(GetField<uint8_t>(VT_TESTBOOL, 0)); }
+  bool testbool() const { return GetField<uint8_t>(VT_TESTBOOL, 0) != 0; }
   bool mutate_testbool(bool _testbool) { return SetField(VT_TESTBOOL, static_cast<uint8_t>(_testbool)); }
   int32_t testhashs32_fnv1() const { return GetField<int32_t>(VT_TESTHASHS32_FNV1, 0); }
   bool mutate_testhashs32_fnv1(int32_t _testhashs32_fnv1) { return SetField(VT_TESTHASHS32_FNV1, _testhashs32_fnv1); }