How do you cast away const'ness when the function takes a reference to the object (and access non-const methods)?

Question

I have a back up copy of data that I would like to protect so I made it const. I need to violate that constness on two occassions, once to store vi

Answer 1

You can circumvent this problem by simply marking all methods as const, except RemoveAll and CopyFrom, the latter being made to be a method of BlkArray that either implements the logic or passes *this to CopyInto.

To be more secure about who can clear the data / copy new stuff into it, you may make those methods private and declare the necessary classes as friends, or use the passkey pattern to protect those two methods.

Answer 2

There is a little trick I learned looking at Qt's internals:

MyClass:circunventConst() const
{
    MyClass* that = const_cast<MyClass*>(this);
    that->myProtectedVariable = value;
}

Answer 3

Be aware that if you do this and the object really is const, then modifying it after casting away the constness is undefined behaviour.

fgBlocks.CopyInto(const_cast<BlkArray&>(backUpCopy));

Same thing for the other one:

const_cast<BlkArray&>(backUpCopy).RemoveAll(true);