Understanding Deployment Targets in Xcode 12: A Guide for Developers

When developing a software application using Qt, it's essential to understand how deployment targets work in Xcode 12. This knowledge will help you avoid common issues and ensure your application runs smoothly on various macOS versions.

The deployment target refers to the lowest version of macOS that your application is compatible with. If you set the deployment target too low, your binary may crash at runtime when deployed to a lower version of macOS than what Qt expected to run on. To avoid this, it's crucial to understand how to set the deployment target correctly.

In Xcode 12, you can control the deployment target using the CMAKE_OSX_DEPLOYMENT_TARGET or QMAKE_MACOSX_DEPLOYMENT_TARGET variables. These variables have a default value set by Qt, which you should not change unless you know that your own code uses macOS APIs that are only available in a particular version higher than what Qt defaults to.

If you try to run your binary on a lower macOS version than the deployment target, Qt will give an error message and the application will not run. This is because Qt checks at runtime whether or not a platform feature is available before utilizing it.

In theory, this would allow running your application on every single macOS version released. However, for practical (and technical) reasons, there is a lower limit to this range, known as the deployment target of your application.

Building an application using Xcode 12's SDK-based development involves weak linking, which allows you to build your application against the headers and libraries of the latest platform SDK while still allowing it to be deployed to macOS versions lower than the SDK version. This technique is used extensively in building for macOS.

In summary, understanding deployment targets in Xcode 12 is crucial for ensuring your Qt-based applications run smoothly on various macOS versions. By setting the deployment target correctly and using weak linking techniques, you can ensure that your application is compatible with a wide range of macOS versions. For more information about SDK-based development on macOS, see Apple's developer documentation.

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