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

[m.sue]

@stephane78

Hi,

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.

-Michael.

[stephane78]

@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)

[m.sue]

@stephane78

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

-Michael.

[stephane78]

@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.

[J.Hilk]

@stephane78
hi,
I have a hard time understanding what exactly is the problem! Any chance you could post the whole lampda here?

[m.sue]

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

-Michael.

[stephane78]

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

[stephane78]

@stephane78 these are my own functions...

[stephane78]

here is the lambda

connect(reponse,&QNetworkReply::finished,reponse,[this,reponse](){
        
       

      


   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;
    if(this->flag)
        dup = QDateTime::fromString(jsonObject["updated_at"].toString(),"yyyy-MM-dd HH:mm:ss");
   
  
  
    int code=jsonObject["code"].toInt();


if(idFichier > 0)
{
         if(!this->flag)
            this->pf->setId(idFichier);
         if(this->flag)
             this->pf->setDateUpload2(dup);
         else this->pf->setDateUpload2(du);
         ....

[stephane78]

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....

[stephane78]

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

[m.sue]

@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;
connect(reponse,&QNetworkReply::finished,reponse,[&dateUpload,response](){
...
});

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

-Michael.

[stephane78]

@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*....

[stephane78]

@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;
 connect(reponse,&QNetworkReply::finished,reponse,[this,&pf2,reponse](){

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

[stephane78]

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

[stephane78]

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

[stephane78]

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......).

[stephane78]

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())) ;

       loop.exec();

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

[stephane78]

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