Question

I am working on a project based on facerecognition using Qt and Opencv in Windows 7. I have come across a really dead end now…I need to train a face recognizer using some images…but whenever I comment out the train statement, the program runs fine but not witholding my purpose…

void Dialog::on_btnAdd_2_clicked()
{
    tmrTimer->stop();

    dir=QDir(directory);
    QFileInfoList files;
    QFileInfo file;
    QString filen;


    dir.setFilter(QDir::Files | QDir::Hidden | QDir::NoSymLinks);
    files=dir.entryInfoList();
    int nofiles;
    nofiles=files.size();
    for(int i=0;i<nofiles;i++)
    {
        file=files.at(i);
        filen=file.absoluteFilePath();


        std::string fname = filen.toStdString();

        filen=file.baseName();
        std::string filename=filen.toStdString();

        char* path = new char [fname.size()+1];
        char name[10];

        strcpy(name,filename.c_str());
        strcpy( path, fname.c_str() );

        name[1]='\0';

        ui->boxConsole->appendPlainText(path);
        ui->boxConsole->appendPlainText(name);

        cv::Mat temp=cv::imread(path,-1);
        newImages.push_back(temp);
        newLabels.push_back(atoi(name));
    }


    ui->boxConsole->appendPlainText("Training Started....!!");

    cv::Ptr<cv::FaceRecognizer> model = cv::createEigenFaceRecognizer();

    model->train(newImages,newLabels);   ///training statement

    //strcat(home,"\\data.xml");


    //model->save(home);


    ui->boxConsole->appendPlainText("Training Completed!!");
    tmrTimer->start();
}

When I run the project and click a button that initiate the above function the process crashes saying…

Problem signature:
  Problem Event Name:   APPCRASH
  Application Name: QtTracker3.exe
  Application Version:  0.0.0.0
  Application Timestamp:    5101dde0
  Fault Module Name:    libopencv_core242.dll
  Fault Module Version: 0.0.0.0
  Fault Module Timestamp:   50da6896
  Exception Code:   c0000005
  Exception Offset: 000a38f0
  OS Version:   6.1.7600.2.3.0.256.1
  Locale ID:    1033
  Additional Information 1: 0a9e
  Additional Information 2: 0a9e372d3b4ad19135b953a78882e789
  Additional Information 3: 0a9e
  Additional Information 4: 0a9e372d3b4ad19135b953a78882e789

Read our privacy statement online:
  http://go.microsoft.com/fwlink/?linkid=104288&clcid=0x0409

If the online privacy statement is not available, please read our privacy statement offline:
  C:\Windows\system32\en-US\erofflps.txt

i modified the code as follows taking advices…and got in to another problem…

void Dialog::on_btnAdd_2_clicked()
{
    tmrTimer->stop();

    dir=QDir(directory);
    QFileInfoList files;
    QFileInfo file;
    QString filen;

    char name[10];
    int i,j;
    std::string str;


    dir.setFilter(QDir::Files | QDir::Hidden | QDir::NoSymLinks);
    files=dir.entryInfoList();
    int nofiles;
    nofiles=files.size();

    for(i=0;i<nofiles;i++)
        {
            file=files.at(i);
            filen=file.baseName();
            std::string filename=filen.toStdString();
            strcpy(name,filename.c_str());

            for(j=0;name[j]!='-';j++);
            name[j]='\0';

            filen=file.absoluteFilePath();
            str=filen.toStdString();

            cv::Mat offimage=cv::imread(str.c_str(),-1);

            cv::namedWindow("face",WINDOW_AUTOSIZE);     //show retrieved image in a window
            cv::imshow("face",offimage);
            cvvWaitKey(1000);

            newImages.push_back(offimage);
            newLabels.push_back(atoi(name));


        }

i removed the pointers used within the for loop and stil the very same problem persists…

I also found that qt creator in its issues tab reported an issue:

:-1: warning: auto-importing has been activated without --enable-auto-import specified on the command line.

Answer 1

When your code crashes, use a debugger to find out where it crashes. If you don’t understand the reason, add the backtrace to the question.

I assume your crash is in the filename handling when looping over the files.
You’re opening multiple cans of worms by using char* instead of the std::string or QString and not doing it properly.

For once, this is highly unsafe and also insecure (buffer overflow):

    char name[10];
    ...
    strcpy(name,filename.c_str());

If the file name is longer than 9, the behavior is undefined (crash, most likely).

You’re also leaking memory, as this allocation is never freed: char* path = new char [fname.size()+1];

So I strongly suggest to use QString instead of fiddling with char*. If you need to pass a char* to OpenCV, you can do it like this:

const QByteArray ba = filename.toLatin1(); //or toUtf8(), toLocal8Bit(), depending on the encoding you need
... functionTakingChar( ba.constData(), -1 ); // or .data(), if imread() takes a non-const char

imread takes a std::string, so:

... imread( filename.toStdString(), -1 );