Question

What if I have this:

union{     vector<int> intVec ;     vector<float> floatVec ;     vector<double> doubleVec ; } ; 

Of course, I’ll be using just one of the 3 vectors. But… what happens when all the 3 vectors are contructed??
Would the consructors of the 3 vectors interfere with each other?? (since the 3 of them are in the same memory address)

Thanks.

Answer 1

Current C++ standard does not allow non-POD types inside unions. You will get this compiler error from gcc:

error: member ‘std::vector<int, std::allocator<int> > <anonymous union>::i’ with constructor not allowed in union error: member ‘std::vector<int, std::allocator<int> > <anonymous union>::i’ with destructor not allowed in union 

New C++ standard (C++0x) proposes unrestricted unions, but it adds yet more object lifetime pitfalls to C++.