Create empty json array with jsoncpp

Question

I have the following code:

void MyClass::myMethod(Json::Value& jsonValue_ref)
{
    for (int i = 0; i <= m_stringList.size(); i++)
    {
        if (m_boolMarkerList[i])
        {
            jsonValue_ref.append(stringList[i]);
        }
    }
}

void MyClass::myOuterMethod()
{
    Json::Value jsonRoot;
    Json::Value jsonValue;
    
    myMethod(jsonValue);

    jsonRoot["somevalue"] = jsonValue;
    Json::StyledWriter writer;
    std::string out_string = writer.write(jsonRoot);
}
    

If all markers in m_boolMarkerList are false, the out_string is { "somevalue" : null }, but I want it to be an empty array: { "somevalue" : [ ] }

Does anybody know how to achieve this?

Thank you very much!

Answer 1

Here are two ways you can do it:

jsonRootValue["emptyArray"] = Json::Value(Json::arrayValue);
// or 
jsonRootValue["emptyArray"] = Json::arrayValue;

Answer 2

You can do this by defining the Value object as an "Array object" (by default it makes it as an "object" object which is why your member becomes "null" when no assignment made, instead of [] )

So, switch this line:

 Json::Value jsonValue;
 myMethod(jsonValue);

with this:

Json::Value jsonValue(Json::arrayValue);
myMethod(jsonValue);

And voila! Note that you can change "arrayValue" to any type you want (object, string, array, int etc.) to make an object of that type. As I said before, the default one is "object".

Answer 3

OK I got it. It is a little bit annoying but it is quite easy after all. To create an empty json array with jsoncpp:

Json::Value jsonArray;
jsonArray.append(Json::Value::null);
jsonArray.clear();
jsonRootValue["emptyArray"] = jsonArray;

Output via writer will be:

{ "emptyArray" = [] }