The QR-Code-Generator library by Project Nayuki for C++ gives you an easy, fast and correct way to generate QR codes. However, you get just a data structure, showing that data is up to you. An example is provided to print the code to a terminal, but not to create and actual image file. For Java, there is an example provided which writes a PNG file, but not for C++. The author of the library also has another C++ library, Tiny-PNG-Out. It is correct up until 700 megapixel PNG files, which I hope your QR code never hits. I've written a class which bridges the two together, allowing you to both generate the QR code and write it to a PNG file, scaled up to be as readable as possible.