c++ implementation to library

Can you create a C ++ library to use QT or just document your implementation?

I believe there is no active new developments in ReadiumSDK (C++ native code), just maintenance. Contributions are welcome. What is your use case? What hardware / software platform do you need to integrate with?

I want to integrate your code into android/ios in qt creator with c++ and qml

I just want to know how to use your C++ source code to open epub books

I would suggest trying one of the 3 "launcher apps" (Android, iOS, OSX), and study the code to see how the "open book" function is used. For example, Android:
https://github.com/readium/SDKLauncher-Android/blob/438da1ede63fa5146153352b9322e454854b550a/SDKLauncher-Android/app/src/main/java/org/readium/sdk/android/launcher/ContainerList.java#L141

readium-sdk/Platform/Android/epub3/src/main/jni/epub3.cpp

Line 468 in 80a71fe

JNIEXPORT jobject JNICALL

iOS:
https://github.com/readium/SDKLauncher-iOS/blob/579a41ac3e8627950edffa5328ea56f187462efa/Classes/ContainerController.m#L57

readium-sdk/Platform/Apple/RDServices/Main/RDContainer.mm

Line 71 in 80a71fe

ePub3::ErrorHandlerFn sdkErrorHandler = ^(const ePub3::error_details& err) {