CodeQL library for C/C++
codeql/cpp-all 1.1.0 (changelog, source)

Member predicate Class::getABaseClassByteOffset

Gets the byte offset within this of each base class subobject of type baseClass, or zero if baseClass and this are the same type. Both direct and indirect base classes are included. Note that for virtual base classes, and non-virtual base classes thereof, this predicate assumes that this is the type of the complete most-derived object.

int getABaseClassByteOffset(Class baseClass)