Path: utzoo!utgpu!watmath!clyde!att!ttrdc!ttrde!pfales
From: pfales@ttrde.UUCP (Peter Fales)
Newsgroups: comp.sys.ibm.pc
Subject: Finding free space on a joined drive
Message-ID: <812@ttrde.UUCP>
Date: 9 Jan 89 15:19:32 GMT
Organization: AT&T, Skokie, IL
Lines: 58


Someone was asking how to find out how much space is available on
a drive, when that drive has been JOINed to another directory.  At least
one solution has been posted, but I think the following method is much 
simpler, even though it also depends on an undocumented DOS function.
(This is function is documented in Ralf Brown's interrupt list, an
excellent reference, which has been posted to the net).

------------------------------ cut here -------------------------------------

/****************************************************************************

    FUNCTION: DiskFreeSpace

    PURPOSE: Returns number of free bytes on selected disk.  Argument
	is a path to a file or directory on the selected disk.  If the
	file is actually on a JOINed drive, the amount of free space
	on the joined drive will be returned.

****************************************************************************/

#include <dos.h>

long
DiskFreeSpace(char *path)
{
	union	REGS r;
	struct 	SREGS s;
	char 	buffer[80];

/* Use the undocumented DOS function 0x60 to map a relative path to a fully
qualified path name.  Then use the first character of that pathname to
determine the drive to which that path belongs.  The key thing here is
that it works even if the path is on another drive that has been JOINed */
	r.x.ax = 0x6000;
	r.x.si = (unsigned)path;	/* ds:si is input path */
	segread(&s);
	r.x.di = (unsigned)buffer;	/* es:di is output path */
	s.es = s.ds;
	intdosx(&r,&r,&s);

/* The first character of the returned path is the drive name, so we
use function 0x36 to read the free space */

	r.x.ax = 0x3600;
	r.x.dx = buffer[0]-'A'+1;
	intdos(&r,&r);
			/* Returns: Sectors/cluster in ax 
				    Bytes/sector in cx
				    Available clusters in bx 
			*/
	return((long)r.x.bx * r.x.cx * r.x.ax);
}
-- 
Peter Fales			AT&T, Room 2F-217
				200 Park Plaza
UUCP:	...att!ttrde!pfales	Naperville, IL 60566
Domain: pfales@ttrde.att.com	work:	(312) 416-5357