Union variable in api calls

Hello

I'm trying to call an API Function that is declared in Visual C++ from Visual Basic 6. The problem is that one of the variable is a structure and this structure contains a variables union . I need to make the function declaration in order to call the API ans i'm having declaration problems. I would like to know how can i declare a union in Visual Basic or how do i enter a variable union to call the function.

This is the C++ code of the function i'm having trouble with...
SNMPAPI
SNMP_FUNC_TYPE
SnmpMgrRequest(
IN LPSNMP_MGR_SESSION session,
IN BYTE requestType,
IN OUT RFC1157VarBindList *variableBindings,
OUT AsnInteger *errorStatus,
OUT AsnInteger *errorIndex
);

Thanks in advance

Dadiel Aguliendos