[quote user="Ines Wieland"]Does it mean, that I have to convert the whole MDL including MDL-Dialogs into C++?[/quote]
No. My intention was to highlight the folly of attempting to implement an outmoded MDL approach to solving a particular problem when C++ offers something better. In this case, the toolSubs_api was an evolution of MDL. Behind the scenes, it provides better file I/O than the orginal MDL but still in a C-style idiom. When building a C++ project, you have to do some extra work to tell the linker where to find the library (*.lib file) that implements those functions.
To put it another way, you can spend time figuring out how to build using the toolSubs_api, which is a dead end. Alternatively, you can learn how to use the C++ file I/O API, which gives you a standard, compiler & linker supported, way of writing better code. Which choice is time better spent?