Constructing array

Question

How to call specific class constructor within operator new[]?

#include <iostream>

class foo
{
  public:
    foo(){std::cout << "\nfoo::foo()\n";}
    foo(int param){std::cout << "\nfoo::foo(int)\n";}
};

int main()
{
  foo* my_array = new foo[45];
  return 0;
}

foo* my_array = new foo[45]; would call foo() constructor. How to call foo(int) constructor?

possible duplicate of Initialize array in constructor without using default constructor or assignment — Stefano Sanfilippo
– Stefano Sanfilippo, Commented Jan 19, 2014 at 15:49

tumdum · Accepted Answer · 2014-01-19 16:03:39Z

4

There is no way to do this for raw arrays. You can achieve similar result with std::vectors' explicit vector (size_type n, const value_type& val = value_type(), const allocator_type& alloc = allocator_type());:

std::vector<foo> my_vector(45, 10);

will create vector with 45 foo objects, each created via foo(10) constructor call.

edited Jan 19, 2014 at 16:03

answered Jan 19, 2014 at 15:49

tumdum

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3 Comments

Borgleader Over a year ago

You can shorten that to std::vector v(45, 10);

typ1232 Over a year ago

Aren't you missing the template parameter <foo>? It's also worth noting, that the constructor gets called only once. The other elements will by copies, so an object that manages ressources has to have a proper copy constructor.

juanchopanza Over a year ago

There is a way to do this for arrays, it is just a bit tedious for long arrays.

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