C / C++ / MFC

class CXMLNode
{
public:
	char *p1;
	char *p2;
};

class AttributeInt 
{
	char * CXMLNode::*m_units;
public:
	AttributeInt(char * CXMLNode::*units = NULL) : m_units(units) {}

	void test()
	{
		if (m_units == NULL)
		{
			printf("m_units is NULL\n");
		}
		else
		{
			printf("m_units is not NULL\n");
		}
	}
};


void main( void )
{ 
	AttributeInt a;
	a.test();

	AttributeInt b(&CXMLNode::p1);
	b.test();
}

You need to use transactions to ensure the integrity of the database. If you are using MFC database classes, see CDatabase::BeginTrans(), CDatabase::CommitTrans() and CDatabase::Rollback(). Also, check that the relationships between the tables are correctly (and completely) defined in Access.