How to put an icon on file extensions of a Qt program on Windows Explorer

[GeneCode]

Hello,

Here is the program. On the Web I found:

QSettings reg("HKEY_LOCAL_MACHINE\\SOFTWARE\\Classes\\.sp\\DefaultIcon",
                 QSettings::NativeFormat);
reg.setValue("Default", "C:\\Users\\Tomy\\Desktop\\package_directory"
               "\\packages\\com.vendor.product\\data\\Spreadsheet.ico");
 
SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, NULL, NULL);

QSettings reg("HKEY_LOCAL_MACHINE\\SOFTWARE\\Classes\\.sp\\DefaultIcon",
                 QSettings::NativeFormat);
reg.setValue("Default", "C:\\Users\\Tomy\\Desktop\\package_directory"
               "\\packages\\com.vendor.product\\data\\Spreadsheet.ico");

SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, NULL, NULL);

To copy to clipboard, switch view to plain text mode 

I put this in void MainWindow::writeSettings() and void MainWindow::readSettings() in the code. And then created an installer using Qt Installer Framework and installed it on Windows.
No icon!
Any idea?

Just find a book and learn it.