Placement new for contiguous memory

Question

I am facing some problems for using placement new for contiguous memory.Please guide me, if there is any other way to do this.
Please refer my code.

#include <new>  
//================================================
class MyClass
{
 private:
    int ma;
 public:
    MyClass():ma(-1){}      
};
//===========================================

int main()
{
    // I am allocating the memory for holding 10 elements of MyClass on heap
    void* pMyClass = ::operator new(sizeof(MyClass)*10);

    //! Note :: the address of pMyClass1 and pMyClass will now point to same   
    //location after calling placement new  

    MyClass* pMyClass1 = :: new(pMyClass)MyClass();  

    //! Problem with this is that, 
    //! i can only instantiate the constructor for the  base address. That is 
    //!  pMyClass[0]. 
    //! If i have to instantiate it for all the other instances, 
    //! that is pMyClass[1] to pMyClass[9], then how to do it ?
    return 0;
}

Answer 1

You have the beginning of the memory in pMyClass, and the stride is sizeof(MyClass). So, what you need to do is for example:

MyClass* pMyClass2 = ::new((MyClass*)pMyClass + 1)MyClass();

Answer 2

Try:

MyClass* pMyClass1 = :: new(pMyClass)MyClass[10];   

Answer 3

You have to call the placement new inside a loop that iterates on the 10 contiguous chunks of memory:

int main()
{
    void* pMyClass = ::operator new(sizeof(MyClass)*10);
    MyClass* pMyClass1 = reinterpret_cast<MyClass*>(pMyClass);
    for (size_t i=0; i<10; ++i) {
        ::new(pMyClass1++)MyClass();
    }
    // ... 
}