what time should I delete the resource

[stampede]

But I still can't figure out what is protected inheritance

It's a kind of "has-a" relationship with possibility to access protected members of contained object. There is more about it, but maybe better leave it alone for now, just focus on the basics.
If you are curious: private and protected inheritance

[stereoMatching]

It's a kind of "has-a" relationship with possibility to access protected members of contained object. There is more about it, but maybe better leave it alone for now, just focus on the basics.
If you are curious: private and protected inheritance

Thanks, but I don't think I would use any protected inheritance since public inheritance
and private inheritance(only some extreme cases would be considered) are capable to mimic most of the cases.