Apple Network Setup Manual do Utilizador descarregar pdf (Página 37)

CHAPTER 2

Using Network Setup

Reading and Writing Preferences 37

IMPORTANT

You can derive the C structure for a speciﬁc preference type

by removing the “k” from the front of the name and the

“Pref” from the end. For example, the C structure for

kOTCfgTCPDHCPLeaseInfoPref is OTCfgTCPDHCPLeaseInfo. The

preference type constants and preference structures for all

of the Apple-deﬁned preferences are provided in Chapter 4,

“Network Setup Protocol Structures and Data Types.” ▲

Reading Variable-size Preferences 2

The MyReadFixedSizePref routine shown in Listing 2-7 also works with variable

size preferences that have a known maximum size that internally includes the

size of the preference. The user-visible name preference

(

kOTCfgUserVisibleNamePref), which contains a packed Pascal string, is an

example. The maximum length of a Pascal string is 256 bytes, and the ﬁrst byte

denotes the length of the actual string data. Listing 2-9 shows how to use

MyReadFixedSizePref to read this type of variable size preference.

Listing 2-9 Reading the user-visible name preference

static OSStatus MyGetEntityUserVisibleName(CfgDatabaseRef dbRef,

const CfgEntityRef *entity,

Str255 name)

{

OSStatus err;

assert(dbRef != nil);

assert(entity != nil);

assert(name != nil);

err = MyReadFixedSizePref(dbRef, entity, kOTCfgUserVisibleNamePref,

name, sizeof(Str255));

return err;

}

If the variable size preference you want to read does not have a known

maximum size and does not store its size internally, you need to know how big

a buffer to allocate before you call

OTCfgGetPrefs. You can get this information

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Apple Network Setup Manual do Utilizador Página 37