【QT】二进制读取图像文件并显示

void MainWindow::showImage()
{
    //打开文件对话框

    QString lastPath="D:/Englishpath/QTprojects/DATA/videoData";
    fileName = QFileDialog::getOpenFileName(this,"OpenFile", lastPath);
    if(fileName.isEmpty())
    {
        QMessageBox::information(this,"Error Message","Select File Failed");
        return;
    }
    QFile file(fileName);
    if(!file.open(QIODevice::ReadOnly))
    {
        QMessageBox::information(NULL,"失败提示","打开失败",QMessageBox::Ok,QMessageBox::Ok);
        return;
    }
//    QTextStream in(&file);
//    ui->textEdit->setText(in.readAll());

    //类型转换为可以被ifstream使用的
    QString str =fileName;
    char *s; QByteArray//QString转换为char*
    ba = str.toLatin1();
    s = ba.data();

    // [1]得到二进制数据;
    using std::ifstream;
    ifstream i_f_stream(s,ifstream::binary);
    i_f_stream.seekg(0, i_f_stream.end);
    int length = i_f_stream.tellg();
    i_f_stream.seekg(0, i_f_stream.beg);
    char *buffer = new char[length];
    i_f_stream.read(buffer, length);//一次性读取
    i_f_stream.close();

    // [2]缓存数据重构;
    QByteArray byteArray(buffer, length);

    // [3] 构建图片对象并载入二进制数据;
    QImage img;
    img.loadFromData(byteArray, "png");

    // [4] 结果检测(将图片保存到某一目录、用label显示);
    img.save(QString("test.bmp"), "png");
    ui->d_label->setPixmap(QPixmap::fromImage(img));

    delete [] buffer;

//    QDataStream in(&file);
//    while( !in.atEnd())
//    {
//        QByteArray s;
//        in >> s;
//        file.close();
//        qDebug()<<s<<endl;
//    }
}