How to resize array in C++?

Question

I need to do the equivalent of the following C# code in C++

Array.Resize(ref A, A.Length - 1);

How to achieve this in C++?

Answer 1

You can do smth like this for 1D arrays. Here we use int*& because we want our pointer to be changeable.

#include // for copy

void resize(int*& a, size_t& n)
{
   size_t new_n = 2 * n;
   int* new_a = new int[new_n];
   copy(a, a + n, new_a);
   delete[] a;
   a = new_a;
   n = new_n;
}

For 2D arrays:

#include // for copy

void resize(int**& a, size_t& n)
{
   size_t new_n = 2 * n, i = 0;
   int** new_a = new int* [new_n];
   for (i = 0; i != new_n; ++i)
       new_a[i] = new int[100];
   for (i = 0; i != n; ++i)
   {
       copy(a[i], a[i] + 100, new_a[i]);
       delete[] a[i];
   }
   delete[] a;
   a = new_a;
   n = new_n;
}

Invoking of 1D array:

void myfn(int*& a, size_t& n)
{
   // do smth
   resize(a, n);
}

Invoking of 2D array:

void myfn(int**& a, size_t& n)
{
   // do smth
   resize(a, n);
}

The declaration of this function should be earlier than one of myfn. And its definition too. These functions were tested and they work correctly.