Dynamic allocation of a class using a char array

How can I use g_classPool to store dynamically allocated instances of class A. I should modify class A, that dynamically allocated instances are stored in the memory occupied by g_classPool. Can also someone tell me how can I learn such features. I was thinking to write void* operator new(...).

char g_classPool[1024];
class A
{
public:
    A(): m_data(42) {}
    ~A() {}
    int getData() { return m_data; }
private:
    int m_data;
};
int main()
{
    A* obj = new A();
    delete obj;
    return 0;
}