c++ - how can i allocate memory for a union member that haven't been initialized -

i have got union of 2 members.

union myunion {     std::wstring mem1;     int mem2;     myunion(std::wstring in){         this->mem1 = in;     }     myunion(int in){         this->mem2 = in;     }     myunion(const myunion& in){         if(this->mem2){             this->mem2 = in.mem2;         }else{             this->mem1 = in.mem1;         }     } }; //and make vector out of union: std::vector<myunion> unions; //but when try push_back: unions.push_back(l"a"); 

it breaks out run time error: 0xc0000005: access violation writing location 0xcccccccc. , when try debug program, realize mem1 have not been allocate memory. don't know why happens , want know how can fix it.

in c++, union not natural datatype, because doesn't fit naturally whole c++ idea of constructors , destructors. when create union in c++, not call constructors of possible types, because writing on top of eachother.

so constructor

myunion(std::wstring in){     this->mem1 = in; } 

will crash because this->mem1's lifetime string has not been started. have use like, call std::string ctor using placement new @ address. later, if change data type, have make sure remember call dtor this->mem1 before start writing different field of union, or memory leakage or corruption.

by far simpler way trying in c++ use variant type boost::variant going handle boilerplate , details you. (union okay if using trivial types no ctors or dtors.)

typedef boost::variant<std::wstring, int> myunion;  std::vector<myunion> unions;  unions.push_back(l"a");