Listing 2-8 – Apple Network Setup User Manual

Page 36

C H A P T E R 2

Using Network Setup

Reading and Writing Preferences

Note

The sample shown in Listing 2-7, which opens and closes
the entity before reading each preference, is implemented
in an inefficient manner for the sake of clarity. If you are
reading multiple preferences, it is more efficient to open the
entity once. Then read the preferences by calling

OTCfgGetPrefs

OTCfgSetPrefs

multiple times and close

the entity when you’re done.

◆

A noteworthy point about reading preferences is that the

OTCfgOpenPrefs

function does not take an area parameter. This is because the

CfgEntityRef

itself

implicitly includes the area. The significant of this point is demonstrated in the
section “Working with Sets” (page 42).

You can use the

MyReadFixedSizePref

routine shown in Listing 2-7 to read

specific preferences within an entity. For example, Listing 2-8 shows how to
read the DHCP lease information from a TCP/IP network connection entity.
The routine calls

MyReadFixedSizePref

, passing it the appropriate preference

type (

kOTCfgTCPDHCPLeaseInfoPref

), a pointer to the corresponding C structure,

and the size of the structure.

Listing 2-8

Reading the DHCP lease info preference in a TCP/IP network
connection entity

static OSStatus MyReadDHCPLeaseInfo(CfgDatabaseRef dbRef,

const CfgEntityRef *entity,

OTCfgTCPDHCPLeaseInfo *dhcpInfo)

{

OSStatus err;

assert(dbRef != nil);

assert(entity != nil);

assert(dhcpInfo != nil);

err = MyReadFixedSizePref(dbRef, entity, kOTCfgTCPDHCPLeaseInfoPref,

dhcpInfo, sizeof(*dhcpInfo));

return err;

}