Retrieve fcbs setting?

[Georg Potthast]

How can you determine with a PBDos program, how many file control blocks have been set with the fcbs=x command in config.sys or config.nt. I use Win98 at the moment. When I call Int21/52, offset 1E/1F in the "Invars" table are zero. The DOS mem command displays the correct fcbs setting, however.

Can anyone tell me where and how the setting is stored by DOS? Reading config.sys/config.nt requires locating these files which seems to be difficult with DOS.

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[Tom Hanlin]

Near as I can find, that information is not available to a DOS program
running under Windows.

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Tom Hanlin
PowerBASIC Staff

[Georg Potthast]

Dear Tom,

thank you for your reply to my post. It is disappointing when you don't get a reply at all.

Your reply inspired me to look further into it and I found that I can retrieve the size
of the fcb area DOS makes depending on the setting of fcbs= in config.sys. From that you
can calculate the number of fcbs.

You could amend this program to retrieve the files=, buffers=, lastdrive= and stacks=
setting too. Details about the dos tables used and interrupts can be found in Ralf Brown's
interrupt list.

This code reads the subsegment control block of the fcb area in memory. It will work from
DOS 4.0 up. I tested it with Win98 and Dos 6.22.

'

defint a-z
cls

'determine location of "invars" table calling int21/ah=52
reg 1,&H5200
call interrupt &H21

'read location of first memory control block from "invars" table
esseg=reg(9)
bxreg=reg(2)
def seg = esseg
mcbseg = peeki(bxreg-2)

'determine if MCB found
def seg = mcbseg
if peek(&H0)=ascii("M") then print "MCB found"

'set to segment of first subsegment control block:
def seg = mcbseg+1

'loop through up to 20 subsegment control blocks to find fcb area ("X")
for i=1 to 20
if instr(chr$(peek(&H0)),any "DEIFXCBLS") then  'subsegment types
	print "SubMCB found: ";
	print chr$(peek(&H0)),peek$(&H08,8)
end if
if chr$(peek(&H0))="X" then  'FCB area found - X is fcb subsegment type
   fcbsize=peeki(&H03)+1     'read size of fcb area in paragraphs and add 1 for SubMCB length
   fcbsize=(fcbsize-1)*16    'determine fcb area in byte
   			     'as displayed by "mem /d /p"
   exit for                  
else                         'read next Subsegment control block
   sbcsize=sbcsize+peeki(&H03)+1    'read and add size of SubMCB
   def seg = mcbseg +1 + sbcsize    'set segment to new SubMCB
end if
next i

if i<20 then
	print "FCBSIZE: ";fcbsize
end if

select case fcbsize  'these values read from the mem /d command
	case 80
        fcbsnumber=1
        case 128
        fcbsnumber=2
        case 192
        fcbsnumber=3
        case 256
        fcbsnumber=4
	case 304
        fcbsnumber=5
        case 368
        fcbsnumber=6
        case 432
        fcbsnumber=7
        case 480
        fcbsnumber=8
        case 544
        fcbsnumber=9
        case 608
        fcbsnumber=10
end select

print "FCBS=";fcbsnumber

end

'

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[This message has been edited by Georg Potthast (edited May 01, 2003).]

[Tom Hanlin]

I tried that approach, but it doesn't return meaningful results under
Windows 2000. Good to hear that you got it working for you.

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Tom Hanlin
PowerBASIC Staff