Doing memcpy on my own? - c++

Question

So, I wondered why I am not able to do memcpy for myself. This is the code that works and gets me the correct result:
unsigned int VTableAddress = FindPattern( VTABLE_PATTERN, VTABLE_MASK );
unsigned int *p_VTable = NULL;
WriteMemory( &p_VTable, ( void* ) ( VTableAddress + 2 ), 4 );
//....
void D3DX9Interface::WriteMemory( void *address, void *bytes, int byteSize )
{
DWORD NewProtection;
VirtualProtect( address, byteSize, PAGE_EXECUTE_READWRITE, &NewProtection );
memcpy( address, bytes, byteSize );
VirtualProtect( address, byteSize, NewProtection, &NewProtection );
}
So for my understanding, WriteMemory basically sets read/write protection to the memory address and then simply copies bytes into address. To understand how things are working, I've tried it myself with this code:
//Get the address of the vtable
unsigned int VTableAddress = FindPattern( VTABLE_PATTERN, VTABLE_MASK );
unsigned int *p_VTable = NULL;
CopyWithRWPrivileges( p_VTable, (unsigned int*)( VTableAddress + 2 ) );
//...
void D3DX9Interface::CopyWithRWPrivileges( unsigned int *p_Destination, unsigned int *p_Source )
{
DWORD Protection( 0 );
VirtualProtect( reinterpret_cast< LPVOID >( p_Destination ), 4, PAGE_EXECUTE_READWRITE, &Protection );
p_Destination = p_Source;
VirtualProtect( reinterpret_cast< LPVOID >( p_Destination ), 4, Protection, &Protection );
}
But for some reason the last code gives me back a NULL pointer. But why?

Answer 1

Ok with the help of UnholySheep I've found the solution for my problem. So first, the pointer is getting copied instead of passed as a reference-pointer. And as second, the p_Source needs to be handled as a pointer too, so with this code it's working:
void D3DX9Interface::CopyWithRWPrivileges( unsigned int *&p_Destination, unsigned int *p_Source )
{
DWORD Protection( 0 );
VirtualProtect( reinterpret_cast< LPVOID >( p_Destination ), 4, PAGE_EXECUTE_READWRITE, &Protection );
p_Destination = *(unsigned int**) p_Source;
VirtualProtect( reinterpret_cast< LPVOID >( p_Destination ), 4, Protection, &Protection );
}