using QPixmap to transparent image

[sophister]

Hi, guys, I want to use QPixmap to translate a PNG picture which is not transparent, into a transparent one. But the following codes does not work, for some compiling errors:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    if(argc < 2)
    {
        //
        std::cout << "no original picture file ！" << std::endl;
        return 0;
    }
 
    QPixmap pix(QString(argv[1]));      //original picture
    pix.setMask(pix.createHeuristicMask());
    QString toWrite("out.png");
    if(argc == 3)
    {
        toWrite = argv[2];
    }
    pix.save(toWrite, "PNG");
    return a.exec();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    if(argc < 2)
    {
        //
        std::cout << "no original picture file ！" << std::endl;
        return 0;
    }

    QPixmap pix(QString(argv[1]));      //original picture
    pix.setMask(pix.createHeuristicMask());
    QString toWrite("out.png");
    if(argc == 3)
    {
        toWrite = argv[2];
    }
    pix.save(toWrite, "PNG");
    return a.exec();
}

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How can the compiler complain that the pix is non-class type"QPixmap"?

Thanks in advance!