CODEWITHSUNDEEP
c++jsonjsoncpp
Martin Meeser
Martin Meeser

Reputation: 2956

Create empty json array with jsoncpp

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!

Upvotes: 22

Views: 46229

Answers (3)

Michal Sabo
Michal Sabo

Reputation: 653

Here are two ways you can do it:

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

Upvotes: 47

Ahmet Ipkin
Ahmet Ipkin

Reputation: 942

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".

Upvotes: 9

Martin Meeser
Martin Meeser

Reputation: 2956

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" = [] }

Upvotes: 5

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