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error on operator= of QDateTime in a lambda, Qt5.6.2

  • Hi, I have an error here

    QDateTime &QDateTime::operator=(const QDateTime &other)
        d = other.d;//error

    inside a lambda function the code was:


    but I have put du as member variable of my object and I have tried :


    setDateUpload was

     void setDateUpload(const QDateTime &value);

    and I have tried with setDateUpload2 that is :

     void setDateUpload2(QDateTime value);

    du is a QdateTime
    this is a parameter of the lambda and is derived of QObject :


    Has someone an idea to help me ?
    I use Qt5.6.2 and I am under windows,here with a debug version of Qt.....

    [Fixed code tags ~kshegunov]

  • there is an error on !old->ref.deref() (more inside, l93 of qshareddata.h)

  • @stephane78


    You can try with a generic reference lambda [&]. Sometimes, depending on the compiler's implementation, lambdas require default objects to be created which may not work in all circumstances.


  • @m.sue what do you mean with generic lambda [&] ? when you pass "this" as argument of the lambda you don't pass it by reference but you can modify all the variable of "this" (with my compiler mingw-w64 and even with visual studio)

  • @stephane78

    I mean replace [this,reponse]() with [&]().


  • @m.sue no ,If I do that, I have an error on reponse->readAll() but I have tried [&,reponse] and I have always the same error on my operator = of QDateTime.

  • Moderators

    I have a hard time understanding what exactly is the problem! Any chance you could post the whole lampda here?

  • ...and setDateUpload(2). I cannot find it as Qt function.


  • @m.sue ```
    void MyFichier::setDateUpload(const QDateTime &value)
    dateUpload = value;
    void MyFichier::setDateUpload2(QDateTime value)
    dateUpload = value;

  • @stephane78 these are my own functions...

  • here is the lambda

       QString strReply = QString::fromUtf8(reponse->readAll());
        QJsonDocument jsonResponse = QJsonDocument::fromJson(strReply.toUtf8());
        QJsonObject jsonObject = jsonResponse.object();
        long idFichier = (long)jsonObject["fileId"].toDouble();
          QDateTime du = QDateTime::fromString(jsonObject["dateUpload"].toString(),"yyyy-MM-dd HH:mm:ss");
        QDateTime dup;
            dup = QDateTime::fromString(jsonObject["updated_at"].toString(),"yyyy-MM-dd HH:mm:ss");
        int code=jsonObject["code"].toInt();
    if(idFichier > 0)
             else this->pf->setDateUpload2(du);

  • I think I could try with the release version because perhaps there isn't any error with the release version.....because here I am with the debug version and with the debugger and with a 64 bits debug version of Qt and Qtcreator....

  • OK this problem is solved, I have put a mutexlocker with a mutex before pf->setid and ml.unlock after setdateupload2 because this is an object associated to a secondary thread with movetothread and now I haven't any more this error. I Have another error further but I put a mutexlocker too and see

  • @stephane78

    There is something fishy with your lambda I think. You do not use &, which means the setDateUpload function works on a copy -> a temporary. You probably will want to work on something like:

    QDateTime &dateUpload=pf->dateUpload;

    EDIT: ok you did not tell about multithreading, either :-)


  • @m.sue I have still the error on operator so I will now try what you said ,but I have already tried with du and dup a members variables of this and it was not good*....

  • @m-sue,Hi michael, thanks a lot,it was fast the solution : I have began to replace all the pointers on the instance of my own class with such a thing in the lambda and it seems to work : for example :

    MyFichier * &pf2=pf;

    and I haven't any problem any more with the QDateTime...

  • I have still a problem with dateupload and seems that the other problems are solved (it seems ) but not for dateupload and shash....

  • still the error on !old->ref.deref()

  • OK, I am not sure that my compiler,mingw-w64 4.9.2, supports well the lambdas and I think I will try with mingw-w64 5.3.0 (but I must build a release and a debug version of Qt and my other libs with it......).

  • so it not mingw 4.9.2. so is there any way to replace the loop.exec() in that code ?

    QNetworkReply * reponse = netmanager->post(requete,multiPart);
         QEventLoop loop;
           connect(reponse, SIGNAL(finished()), &loop, SLOT(quit())) ;

    (but not a lambda because I have problems with the lambda)

  • I post another thread for this...this subject is closed,because I don't see any way for this lambda....

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