c# / c++ interop and out allocated array by c++

Question

I have a thirdparty c++ method in a dll like this:

void GetValues(int *pCount, int **ppValues);

c++ usage would be:

int count = 0, *pValues = NULL;
GetValues(&count, &pValues);
CoTaskMemFree(pValues);

I want to call this method in c#: it is declared as :

void GetValues([out] int pCount, IntPtr ppValues);

c# usage (the method using this code is marked as unsafe):

   int *pValues = null;
    try
    {
       int count;
       GetValues(out count, new IntPtr(&pValues));
       for (var i=0; i<count; i++)
       {
           var val = pValues[i];
       }
    }
    finally
    {
       Marshal.FreeCoTaskMem(new IntPtr(pValues));
    }

this seems to work. But I'm wondering if this is correct or if there are problems with this approach I didin't see.

EDIT: changed c# declaration from void GetValues([out] int pCount, [out] IntPtr ppValues); to void GetValues([out] int pCount, IntPtr ppValues);

Answer 1

Maybe I am missing something, but "out" prefix is missing in call GetValues(out count, new IntPtr(&pValues));

I would solve this problem simpler:

        unsafe void test()
    {
        IntPtr intPtr = IntPtr.Zero;
        try
        {
            int count = 0;
            GetValues(out count, out intPtr);

            int* pValues = (int*)intPtr;

            for (var i = 0; i < count; i++)
            {
                var val = pValues[i];
            }
        }
        finally
        {
            Marshal.FreeCoTaskMem(intPtr);
        }
    }