Print the QGuiApplication::devicePixelRatio() value

qt_pixel_ratio.cc

// This simple utility prints the device pixel ratio reported by Qt library
// How to compile:
// - save into "qt_pixel_ratio" directory
//   (the directory name determines the binary name, see later)
// - run "qmake-qt5 -project"
// - run "qmake-qt5"
// - run "make"
// Then you can run the "./qt_pixel_ratio" binary.
// (Use the name of the parent directory if you used another directory name
// in the first step.)

#include <QGuiApplication>
#include <QScreen>
#include <iostream>

int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);
    
    std::cout << "Pixel Ratio: " << a.devicePixelRatio() << std::endl;
    std::cout << "DPI(x):   " << QGuiApplication::primaryScreen()->physicalDotsPerInchX() << std::endl;
    std::cout << "DPI(y):   " << QGuiApplication::primaryScreen()->physicalDotsPerInchY() << std::endl;
    std::cout << "DPI(avg): " << QGuiApplication::primaryScreen()->physicalDotsPerInch() << std::endl;
}