As stated in cppreference.com class inheritance have underlying rule set.
| Inderited as | Type in Base | Type in Derived |
|---|---|---|
| public | public | public |
| protected | protected | |
| private | unaccessible unless friended | |
| protected | public | protected |
| protected | protected | |
| private | unaccessible unless friended | |
| private | public | private |
| protected | private | |
| private | unaccessible unless friended |