Using Qt to write Cross Platform Library

is anybody know how to use Qt to write cross-platform class library(not a stand-alone program), to be called by other Qt program?

that is, i can use QObject like QString inside the functions in my library, and still can be identify by other Qt program once it has been loaded by QLibrary

Yes, you can create a cross platform library, similar to any other library. What you should do is compile the library as normal on every platform and supply a header file with the definitions of the interface to the library (also as normal). By including that header file in the program, the classes/functions/etc in the library are known and the library can be linked to the program during linking.

So, basically you need to create the following:
libLinux.a
libLinux64.a
libSunOs.a
libDefinitions.h

We do this all the time, but then with modules in the development tree.

You can also create a dynamic library, but I don't have any experience with that.

Add "TEMPLATE = lib" to your project file. If you want your library to be loadable by QLibrary, you also have to make sure that all functions in that library are declared as extern "C":

Code:

---

extern "C" {
  void func1();
  void func2();
  void func3();
  //...
}

---