How to pass and return an array b/w c# script and c++ plugin

Hey

We want to pass an array from c# script to c++ plugin so that c++ plugin can modify that array and we can access it back in c# script. What we are doing is :

c# script :

 [DllImport ("__Internal")]

private static extern void _score_global_all( ref IntPtr ptrResultVerts, ref int resultVertLength);

public int[] get_score_global_all() {

      IntPtr ptrResultVerts = IntPtr.Zero;
      int resultVertLength = 0;
     
 _score_global_all(ref ptrResultVerts,ref resultVertLength);
 
     int [] TestArray;
     TestArray=new int[resultVertLength];
     
     Marshal.Copy(ptrResultVerts
             , TestArray
             , 0
             , resultVertLength);
     
        return TestArray;
 }

c++plugin

void _score_global_all( int* ptrResultVerts , int* resultVertLength) {

     *resultVertLength = 5;
 int count=*resultVertLength;
 
 ptrResultVerts=new int[count];
     for (int i = 0; i < count; i++) {
         ptrResultVerts[i] = 23;    
     }
 
 }

Output in c# script :

resultVertLength=5; // got it right

we get an exception "NullReferenceException" in Marshal.Copy() saying source i.e. ptrResultVerts is null.

Any Idea How to do this right ...? Any other Approach for same with sample code will be appreciated .!!!!

Thanks