get the size of heap array in c++ [duplicate]

Question

Code1:

int * a;
a=new int[222];
cout<<"the size of a is "<<sizeof(a)<<endl;

Output1:

the size of a is 8

Code2:

int * a;
a=new int[222];
cout<<"the size of a is "<<a.length()<<endl;

Output2:

error: member reference base type 'int *' is not a structure or
  union

How to get the size of a heap array? Thanks..

Answer 1

The short answer is, it can't be done, at least not in a portable manner. You'll need to keep track of the array's size separately somehow (e.g. in an integer variable or similar).

Answer 2

Use a container instead of a raw pointer:

std::vector<int> a(222);
cout << "the size of a is " << a.size(); << endl;