Syntax

The syntax of MIB objects is modeled by the OS (Object Syntax) structure:

              typedef int (*IFP) ();

              typedef struct object_syntax {
                   char   *os_name;            /* syntax name */

                   int     os_type;            /* syntax type */
                   IFP     os_decode;
                   IFP     os_free;            /* free data */

               }       *OS;
               #define NULLOS  ((OS) 0)

Internet-standard MIB defined syntaxes

Syntax	Structure type
INTEGER	integer
OctetString	struct _OctetString
ObjectID	struct OIDentifier
NULL	char
DisplayString	struct _OctetString
IpAddress	struct sockaddr_in
NetworkAddress	struct sockaddr_in
Counter	integer
Gauge	integer
TimeTicks	integer
ClnpAddress	struct _OctetString

where ``syntax'' is the name appearing in a compiled MIB module, and ``structure type'' is the C language data type corresponding to the object's syntax. The structure types are described below.

To take a syntax name and get back the structure, use the routine text2syn().

Here are the structures and routines used to implement some of these low-level MIB abstractions: Integer, OctetString, ObjectID, and IPAddress.

INTEGER, Counter, Gauge, and TimeTicks

integer is used for the INTEGER, Counter, Gauge, and TimeTicks syntaxes. The definition is:

            typedef int integer;

OctetString, DisplayString, and ClnpAddress

struct _OctetString is used for the OctetString, DisplayString, and ClnpAddress syntaxes. The definition is:

               typedef struct _OctetString {
                   unsigned char *octet_ptr;   /* list of octets */
                   long     length;            /* number of elements */
               };

ObjectID

struct OIDentifier is used for the ObjectID syntax. The definition is:

               typedef struct OIDentifier {
                   int     oid_nelem;  /* number of sub-identifiers */

                   unsigned int *oid_elements;
                       /* the (ordered) list of sub-identifiers */
               }                       OIDentifier, *OID;
               #define NULLOID ((OID) 0)

IPAddress and NetworkAddress

struct sockaddr_in is used for the IpAddress and NetworkAddress syntaxes. It is assumed that you are familiar with this structure. If not, consult the file /usr/include/sys/netinet/in.h.