what is a qr code and how does it work code example

Example: QR code in QT

#include "QrCode.hpp"

void paintQR(QPainter &painter, const QSize sz, const QString &data, QColor fg)
{

    qrcodegen::QrCode qr = qrcodegen::QrCode::encodeText(data.toUtf8().constData(), qrcodegen::QrCode::Ecc::LOW);
    const int s=qr.getSize()>0?qr.getSize():1;
    const double w=sz.width();
    const double h=sz.height();
    const double aspect=w/h;
    const double size=((aspect>1.0)?h:w);
    const double scale=size/(s+2);
   
    painter.setPen(Qt::NoPen);
    painter.setBrush(fg);
    for(int y=0; y<s; y++) {
        for(int x=0; x<s; x++) {
            const int color=qr.getModule(x, y);  // 0 for white, 1 for black
            if(0!=color) {
                const double rx1=(x+1)*scale, ry1=(y+1)*scale;
                QRectF r(rx1, ry1, scale, scale);
                painter.drawRects(&r,1);
            }
        }
    }
}