Why don't you perform the input validation inside your DLL's function? Veni, vidi, vici.

You're most likely never going to get an answer about this here. It's unlikely, in the extreme, that anyone who has ever used that library will ever see your question here. You're best bet would be to contact the people that wrote the library you're using. A guide to posting questions on CodeProject[^] Dave Kreskowiak

jn4u wrote: Is std::string more neutral to the character set? sadly, no. there is a std::wstring variation to handle wide char strings. image processing toolkits | batch image processing