Ideally, you can build and run the applications created by using Qt and OpenCV frameworks on desktop and mobile platforms alike, without having the need to write any platform-specific codes. However, in practice, this is not as easy as it seems, since frameworks like Qt and OpenCV act as wrappers over the capabilities of the operating system itself (in some cases), and since they are still undergoing extensive development, there might be some cases that are not yet fully implemented in a particular operating system, such as Android or iOS. The good news is that those cases are getting rarer as new versions of the Qt and OpenCV frameworks are released, and even now (Qt 5.9 and OpenCV 3.3), most of the classes and functions in both of these frameworks can be easily used in Windows, Linux, macOS, Android, and iOS operating systems.
So, first...
