pinvoke_ex.cs

static extern void MyPInvoke(IntPtr ptrToCstr)

static void Main()
{
  IntPtr ptr = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(IntPtr)));
  try
  {
    MyPInvoke(ptr);
    IntPtr cstrPtr = Marshal.PtrToStructure(ptr, typeof(IntPtr))
    string myStr = (string)Marshal.PtrToStringAnsi(cstrPtr)
  }
  finally
  {
    Marshal.DeallocHGlobal(ptr);
  }
}