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!
