Question

I have a large application written in Delphi. I want to renew it, starting with the user interface. I thought about using the new Qt. During the process of renewing it, I want to change to C++ as the programming language.
Is there a way to gradually rewrite the application (starting with the UI) to change to C++?

Thank you for your help.

Answer 1

The best course of action highly depends on the C++ development environment.

If it is C++ Builder you have two possibilities:

• Use runtime packages instead of normal DLLs. This will spare you much headaches when it comes to string marshalling and mapping class hierarchies to flat DLL functions.

• Use mixed code. You can mix Delphi/Pascal code with C++ code in the same project. (Only one language in a single module/unit though)

If it is any other C++ compiler:

• Go the way you proposed with DLLs. You have to create some kind of layer/facade to map your classes’ functionality to flat DLL functions.

• If you want to go the plain DLL way even though you are using C++ Builder you can try using a shared memory manager like ShareMem (comes with Delphi) or FastMM (SourceForge) to allow passing of strings instead of PChars.

• Create .objs instead of .dcus so both compilers work with the same output format. Then link them directly into you C++ program. This is essentially the same as with creating a DLL, but it’s static. You will spot certain kinds of errors at compile time rather than runtime.