In a Qt project, you can set the application icon for different platforms by following these steps

1. Setting the Icon for Windows

• Create an .ico file (this can contain multiple resolutions in one file).
• Place the .ico file in your project directory.
• In your .pro file, add the following line to reference the icon file:
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  RC_ICONS = path/to/icon.ico
• This line tells Qt to include the .ico file in the build, so it will appear as the application icon on Windows.

2. Setting the Icon for macOS

• Create an .icns file (specific to macOS).
• Place the .icns file in your project directory.
• In the .pro file, add:
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  ICON = path/to/icon.icns
• This will set the application icon for macOS applications.

3. Setting the Icon for Linux

• For Linux, you generally set the icon for the application window, rather than the app file itself.
• In your main code, use the setWindowIcon() method on the main window:
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  QIcon icon("path/to/icon.png"); mainWindow.setWindowIcon(icon);
• Note that Linux desktop environments often require .desktop files to specify application icons system-wide. This file typically goes in /usr/share/applications and references your icon.

By adding these settings to your project, Qt will package the icon for the respective platforms.