no match for 'operator[]' (operand types are 'QVariant' and 'const char [2]') QVariant/QVariantMap

Question

Im trying to make the start of a wrapper class for json in qt 5.1 and i'm working on a function which which will check if the var inputted is a QVariantMap or just a QVariant and everything works well till i go the second level of the muli dimen array. here is my array structure and class code.

JsonHelper jh;
QVariantMap obj = jh.getJsonObjectVarientMap(data);

This causes me the problems, when i just use "obj" or "obj["1"]" there is no issues, only when i

 // obj["4"]["3"] this causes the problems
qDebug() <<  "Your returned val is : " << jh.keySearchVal(obj["4"]["3"],arr_index_txt);
QMap<QString,QVariant> mp = obj["4"].toMap();
foreach(QString key,mp.keys())
{
    // this works ok
    qDebug() << "key : " << key << " : val : " << mp[key];
}

QVariantMap JsonHelper::getJsonObjectVarientMap(QString in)
{
    QJsonDocument d = QJsonDocument::fromJson(in.toUtf8());
    return d.object().toVariantMap();
}

QVariant JsonHelper::keySearchVal(QVariant source, QString key)
{
    QString type(source.typeName());
    if(type=="QVariantMap")
    {
        QMap<QString, QVariant> map = source.toMap();
        foreach(QString key_inner,map.keys())
        {
            QVariant in = map[key_inner];
            if(key_inner==key)
            {
                return getVariantVal(in);
            }
        }
    }
    return "";
}

QVariant JsonHelper::keySearchVal(QVariantMap source, QString key)
{
    foreach(QString key_inner,source.keys())
    {
        if(key_inner==key)
        {
            return source[key_inner];
        }
    }
    return "";
}

     QVariant JsonHelper::getVariantVal(QVariant in)
     {
    qDebug() << "from variant";
    QString type(in.typeName());
    if(type=="QVariantMap")
    {
        return in.toMap();
    }
    return in;
}

Answer 1

// obj["4"]["3"] this causes the problems

That is invalid because QVariant does not have an operator[] overload. That is also what the compiler is trying to tell you with this:

no match for 'operator[]' (operand types are 'QVariant' and 'const char [2]') QVariant/QVariantMap

You will need to convert any nested QVariant explicitly to QVariantMap if that is the underlying data type. See the following method for details:

QMap QVariant::toMap() const

Returns the variant as a QMap if the variant has type() QMetaType::QVariantMap; otherwise returns an empty map.

It is not the main point, but you also have two further issues:

• You seem to use the word Varient as opposed to Variant.

• Your code lacks error checking and reporting for conversions, etc.