test if val["1"]["2"]["3"] is bool

jsoncpp_test_field.cpp

Json::value val;
val = val["1"];
if (val.isNull() || !val.isObject()) {
  return false;
}
val = val["2"];
if (val.isNull() || !val.isObject()) {
  return false;
}
val = val["3"];
if (!val.isBool()) {
  return false;
}