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MIB object instances are modeled by the OI (Object Instance) structure:
typedef struct object_instance {
	OID     oi_name;      /* instance OID */
	OT      oi_type;      /* prototype */
} object_instance, *OI;
#define NULLOI  ((OI) 0)
There are several routines to manipulate MIB instances;
these are described in
smux_util(3snmp).