Question

I’m not sure if this will be a specific thing with jsoncpp or a general paradigm with how to make a C++ library behave better. Basically I’m getting this trace:

imagegeneratormanager.tsk: src/lib_json/json_value.cpp:1176: const Json::Value&     Json::Value::operator[](const char*) const: Assertion `type_ == nullValue || type_ == objectValue' failed.

That happens when the input is bad. When the input – which is coming from another application of mine via memcached – happens to be bad, I would like to handle this error. You know, gracefully. Perhaps something like, “error: input for item 15006 is bad” going to the log. Not crashing my entire JSON-string-processing task.

Is this just a badly written library or is it possible to configure it more subtly?

Edit: here’s some calling code:

Json::Value root;
Json::Reader reader;
succeeded = reader.parse(jsonString, root);

if(!succeeded) {
  throw std::runtime_error(std::string("Failed to parse JSON for key ")  + emailInfoKey.str());
}

std::string userEmail = root.get("userId", "").asString();
std::string bodyFilePath = root.get("bodyFilePath", "").asString();
std::string msgId = root.get("msgId", "").asString();

Answer 1

According to the library reference:

Value & Json::Value::operator[] ( const StaticString & key )

Access an object value by name, create a null member if it does not exist.

Seems you are trying to call operator[] on a non-object, say an integer or a string (get internally uses operator[]). You are breaking the function precondition, and its an error on your side of the code, not the library. You could check if the Json::Value is an object before accessing it as such using isObject().