Direct manipulation of CLI arrays using native pointers

Here’s some code that shows how you can directly manipulate the contents of an array using native pointers. The first sample is for a single dimensional array and the second is for a jagged array.

Natively accessing a single-dimensional array

void Test1()
{
    array<int>^ arr = gcnew array<int>(3);
    arr[0] = 100;
    arr[1] = 200;
    arr[2] = 300;

    Console::WriteLine(arr[0]);
    Console::WriteLine(arr[1]);
    Console::WriteLine(arr[2]);

    /*
    Output :-
      100
      200
      300
    */

    // Modifying the array using a native int*
    // that points to a pinned pointer in GC'd heap
    pin_ptr<int> p1 = &arr[0];
    int* p2 = p1;
    while(*p2)
    {
        (*p2)++;
        p2++;
    }

    Console::WriteLine(arr[0]);
    Console::WriteLine(arr[1]);
    Console::WriteLine(arr[2]);

    /*
    Output :-
      101
      201
      301
    */
} 

Natively accessing a jagged array

void Test2()
{
    array<array<int>^>^ arr = gcnew array<array<int>^>(2);
    arr[0] = gcnew array<int>(2);
    arr[1] = gcnew array<int>(2);
    arr[0][0] = 10;
    arr[0][1] = 100;
    arr[1][0] = 20;
    arr[1][1] = 200;

    Console::WriteLine(arr[0][0]);
    Console::WriteLine(arr[0][1]);
    Console::WriteLine(arr[1][0]);
    Console::WriteLine(arr[1][1]);

    /*
    Output:
      10
      100
      20
      200
    */


    // Copying the managed jagged array to
    // a native array of pointers and accessing
    // the members using the native array
    pin_ptr<int> p1 = &arr[0][0];
    pin_ptr<int> p2 = &arr[1][0];
    int* p3[2];
    p3[0] = p1;
    p3[1] = p2;

    Console::WriteLine(p3[0][0]);
    Console::WriteLine(p3[0][1]);
    Console::WriteLine(p3[1][0]);
    Console::WriteLine(p3[1][1]);

    /*
    Output:
      10
      100
      20
      200
    */

    // Assigning the native array of pointers
    // to a native int** and modifying the array
    int** p4 = p3;
    for(int i=0; i<2; i++)
        for(int j=0; j<2; j++)
            p4[i][j] += 3;

    Console::WriteLine(arr[0][0]);
    Console::WriteLine(arr[0][1]);
    Console::WriteLine(arr[1][0]);
    Console::WriteLine(arr[1][1]);

    /*
    Output:
      13
      103
      23
      203
    */
}

Essentially we use a pinning pointer to the GC’d heap and then treat the casted native pointer as if it were pointing to a native array. Gives us a really fast method to manipulate array content!