[c++] How to resize array in C++?

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++?

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

#include<algorithm> // 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<algorithm> // 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);
}
  


   

You cannot do that, see this question's answers. You may use std:vector instead.

Raw arrays aren't resizable in C++.

You should be using something like a Vector class which does allow resizing..

std::vector allows you to resize it as well as allowing dynamic resizing when you add elements (often making the manual resizing unnecessary for adding).

1. Use std::vector or
2. Write your own method. Allocate chunk of memory using new. with that memory you can expand till the limit of memory chunk.

You cannot resize array, you can only allocate new one (with a bigger size) and copy old array's contents. If you don't want to use std::vector (for some reason) here is the code to it:

int size = 10;
int* arr = new int[size];

void resize() {
    size_t newSize = size * 2;
    int* newArr = new int[newSize];

    memcpy( newArr, arr, size * sizeof(int) );

    size = newSize;
    delete [] arr;
    arr = newArr;
}

code is from here http://www.cplusplus.com/forum/general/11111/.