Question

I understand that const_cast to remove constness of objects is bad,

I have the following use case,

//note I cannot remove constness in the foo function foo(const std::vector<Object> & objectVec) {     ...    int size = (int) objectVec.size();    std::vector<Object> tempObjectVec;    //Indexing here is to just show a part of the vector being    //modified    for (int i=0; i < (int) size-5; ++i) {        Object &a = const_cast<Object&> objectVec[i];        tempObjectVec.push_back(a);    }     foo1(tempObjectVec); }   

If i change tempObjectVec objects in foo1, will the original objects in ObjectVec change, I say yes since I am passing references, further is this efficient. Can you suggest alternatives.

Answer 1

Well, that depends on Object. But the Objects are being copied, when you pass them to push_back. You can check this by adding some debug code to the copy constructor. So if Object is well-behaved and keeps distinct copies separate, then foo1 can change the vector it gets all it likes.

A more efficient way to do this would be to have foo1 accept a start and end iterators:

void foo1(std::vector<Object>::const_iterator start,           std::vector<Object>::const_iterator end);  ... foo1(objectVec.begin(), objectVec.end() - 5); 

If you don’t use const_cast, then the type system will ensure that foo1 does not change any elements, as these are const_iterators.