0xFF

https://stackoverflow.com/questions/6163683/cycles-in-family-tree-software

I am the developer of some family tree software (written in C++ and Qt). I had no problems until one of my customers mailed me a bug report. The problem is that the customer has two children with their own daughter, and, as a result, he can't use my software because of errors.

The problem, in our case, and I assume your case as well, comes from the GEDCOM format that is extremely opinionated about what a family should be. However this format contains some severe misconceptions about what a family tree really looks like. GEDCOM has many issues, such as incompatibility with same sex relations, incest, etc... Which in real life happens more often than you'd imagine (especially when going back in time to the 1700-1800).