Inside Macintosh: Networking With Open Transport / Part 2 - Open Transport Reference

Chapter 27 - Utilities Reference / Constants and Data Types

The Get Link Object Macro

Open Transport defines a macro (OTGetLinkObject) that you can use to easily cast back to the original object from a pointer to either a LIFO or a FIFO linked list structure.

DataType* OTGetLinkObject(OTLink* linkPtr, 
                                         DataType structName, 
                     NameOfLinkPtrField fieldName)

#define OTGetLinkObject(link, struc, field)

\
((struc*)((char*)(link) - offsetof(struc, field)))

PARAMETERS

linkPtr

A pointer to the OTLink structure from which you wish to cast back.

structName

The name of the structure containing the OTLink structure.

fieldName

The OTLink field in the above structure.

function result

The macro results in a pointer to the appropriate data type by offsetting the linkPtr appropriately and casting the result.