c++ - Problem allocating derived class array with new -

i have simple program

$ cat a.cpp  #include <iostream> class myclass {     public:         virtual void check() {             std::cout << "inside myclass\n";         } };  class myclass2: public myclass {     public:         int* a;         virtual void check() {             std::cout << "inside myclass2\n";         } };  int main() {     myclass *w, *v;     w = new myclass2[2];     v = new myclass2;     std::cout << "calling w[0].check\n"; w[0].check();     std::cout << "calling v->check\n"; v->check();     std::cout << "calling w[1].check\n"; w[1].check(); } $ g++ a.cpp $ ./a.out  calling w[0].check inside myclass2 calling v->check inside myclass2 calling w[1].check segmentation fault 

i thought possible use new allocate derived class objects. also, v->check() seems work fine.

w = new myclass2[2];  

this creates array of 2 myclass2 objects. of type myclass2[2]. new expression returns pointer initial element of array , assign pointer w.

w[1].check();   

this treats w pointer array of myclass objects, not array of myclass2 objects.

you cannot treat array of derived class objects if array of base class objects. if want able use derived-class objects, need array of pointers:

myclass** w = new myclass*[2]; w[0] = new myclass2; w[1] = new myclass2;