ParamBlockRec Union Reference

#include <Files.h>

Data Fields
IOParam	ioParam
FileParam	fileParam
VolumeParam	volumeParam
CntrlParam	cntrlParam
SlotDevParam	slotDevParam
MultiDevParam	multiDevParam

Detailed Description

   
Note
 
All six structures on this union share the same names for the first eight
fields (the first 24 bytes). These common fields are defined in a macro
called the ParamBlockHeader .
In lieu of Pascal's system of records and variants, C programmers can use
predefined unions to access the various parts of the file system parameter
blocks. There are several options, but a common way to access the data is by
allocating a union (ie, storage for the largest of the union-member
structures) and creating pointers which refer to the relevant structure
data types:
ParamBlockRec pb; // allocate a union
ioParam *ipb=(IOParam *) // and structure ptrs
fileParam *fpb=(FileParam *) // all pointing same addr
volumeParam *vpb=(VolumeParam *)
pb.ioParam.ioVRefNum = 2; // as union member field
pb.fileParam. ioFlFndrInfo .fdType = 'TEXT';
pb.volumeParam. ioVolIndex = 0;
ipb->ioVRefNum = 2; // or as a structure field
fpb->ioFlFndrInfo .fdType = 'TEXT';
vpb->ioVolIndex = 0;
You can also do ad hoc type coercion:
unsigned char pb[80]; // big enough to hold a FileParam or IOParam
short theVRef;
theVRef = (( IOParam *)pb)->ioVRefNum;
((FileParam *)pb)-> ioFlLgLen = 1000L;
printf("File type is '%c%c%c%c'\n",pb[32],pb[33],pb[34],pb[35]);
 
 Copyright: THINK Reference © 1991-1992 Symantec Corporation
 

Field Documentation

fileParam

FileParam ParamBlockRec::fileParam

Used for unopened files

ioParam

IOParam ParamBlockRec::ioParam

Generally used in I/O for open files

volumeParam

VolumeParam ParamBlockRec::volumeParam

Used in volume-specific functions

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The documentation for this union was generated from the following file:

• Files.h