GetVCBQHdr
GetVCBQHdr Obtain pointer to the volume control block queue header returns address of a 10-byte QHdr structure GetVCBQHdr returns the standard Operating System queue's header address, which is used to maintain the linked-list of volume control blocks. There is
one VCB entry for every online volume, whether it is currently mounted or not.
qLink field points to the first volume control block in the queue.
Notes: C programmers may prefer to get this address from the global variable
VCBQHdr (at 0x0356). The global variable DefVCBPtr points directly to
the VCB of the current default volume. It is probably a mistake to manipulate this queue directly, but if you need
to, you can use the OS Utilities functions En queue and De queue, passing
VCBQHdr as the queue you wish to modify.
Nearly everything you'll ever want to know about volumes can be obtained
via PBGetVInfo (which lets you easily index through the list).
If you are running under HFS, the queue elements are 178-byte VCB structures. If you booted with a flat file system, the queue is made up of
structures which include only the first 94-bytes of the VCB structure. The qLink field of either structure points to the next such structure in the chain
or is 0 to indicate the end of the chain. The following example illustrates
how to access the VCB queue.
Example
#include <Files.h>
#include <OSUtils.h>
printf("First vcb is at = %lx\n", qhp->qHead );
vcbp = (VCB *)qhp->qHead; /* address of a queue element */ printf("Volume's drive # is: %d\n", vcbp->vcbDrvNum );
printf("number of files in root = %d\n", vcbp->vcbNmFls );
printf("Next vcb is at = %lx\n", vcbp->qLink ); /* 0 means no more */