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up vote 4 down vote favorite
1

I have 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 boolMarkers 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!

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3 Answers

up vote 10 down vote accepted

You can do it also this way:

jsonRootValue["emptyArray"] = Json::Value(Json::arrayValue);
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why not just jsonRootValue["emptyArray"] = Json::arrayValue; –  Konstantin K May 12 at 22:44
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up vote 2 down vote

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".

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Thank you Ahmet but this is exactly the same as user609441 already stated with a little more text. –  Martin Meeser Mar 5 '13 at 11:18
    
Wanted to explain the reasons as well ^_^ –  Ahmet Ipkin Mar 7 '13 at 7:29
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up vote 0 down vote

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" = [] }
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