C++ dynamic allocation of class array -

assume class x constructor function x(int a, int b)

i create pointer x x *ptr; allocate memory dynamically class.

now create array of object of class x

 ptr = new x[sizeofarray]; 

until fine. want creation of above array of objects should invoke constructor function x(int a, int b). tried follows:

ptr = new x(1,2)[sizeofarray];  

as expected gave me compile time error

error: expected ';' before '[' token|

how can create array of objects invoke constructor?

sizeofarray entered user @ runtime.

edit: wanted achieve in not possible answered zenith or complex . how can use std::vector same?

this seems job placement new...

here's basic example:

run online !

#include <iostream> #include <cstddef>  // size_t #include <new>      // placement new  using std::cout; using std::endl;  struct x {     x(int a_, int b_) : a{a_}, b{b_} {}     int a;     int b; };  int main() {     const size_t element_size   = sizeof(x);     const size_t element_count  = 10;      // memory new objects going placed     char* memory = new char[element_count * element_size];      // next insertion index     size_t insertion_index = 0;      // construct new x in address (place + insertion_index)     void* place = memory + insertion_index;     x* x = new(place) x(1, 2);     // advance insertion index     insertion_index += element_size;      // check out new object     cout << "x(" << x->a << ", " << x->b << ")" << endl;      // explicit object destruction     x->~x();      // free memory     delete[] memory; } 

edit: if i've understood edit, want this:

run online !

#include <vector> // init vector of `element_count x x(1, 2)` std::vector<x> vec(element_count, x(1, 2));  // can still raw pointer array such x* ptr1 = &vec[0]; x* ptr2 = vec.data();  // c++11