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Q62218: OS/2 API Function to Get Current Drive

Article: Q62218
Product(s): See article
Version(s): 6.00 6.00b 7.00
Operating System(s): OS/2
Keyword(s): ENDUSER | SR# S900517-70 | mspl13_basic
Last Modified: 7-JUN-1990

Microsoft BASIC Compiler versions 6.00 and 6.00b and Microsoft BASIC
Professional Development System (PDS) version 7.00 protected mode
programs can call the OS/2 API function DosQCurDisk() to get the
currently selected drive. DosQCurDisk() requires the following
parameters:

   Parameter   Description
   ---------   -----------

   PTR WORD    Receives current drive code (1 = A, 2 = B, etc.)

   PTR DWORD   Receives logical drive bitmap (logical drives A-Z
               correspond to bits 0-25; a bit is set if a
               logical drive exists)

The second parameter is not important in getting the current drive,
but it is worthy to note that for API functions a DWORD (4 bytes) has
a BASIC type of LONG. Likewise, a WORD (2 bytes) has a BASIC type of
INTEGER. Since the specification requires pointers to these data
items, the DECLARE statement for DosQCurDisk() uses the SEG keyword for
each of the parameters. This causes 4-byte addresses of the parameters
to be passed instead of 2-byte addresses, which is the default because
BASIC uses the medium-memory model. Also, API functions return an
error code; therefore, for BASIC to retrieve this code, it must
declare DosQCurDisk() as a FUNCTION.

The DECLARE statements for almost every API function are located in
include files that come with BASIC 6.00 and 6.00b and BASIC PDS 7.00.
To modify the DECLARE statement, you just have to include the right
file. See the PACKING.LST file included with the product for a
description of these include files.

This information applies to Microsoft BASIC Compiler versions 6.00 and
6.00b for MS OS/2 and Microsoft BASIC PDS version 7.00 for MS OS/2.

For more information on calling OS/2 API functions from Microsoft
BASIC Compiler versions 6.00 and 6.00b, see Page 21 of the "Microsoft
BASIC Compiler 6.0: User's Guide" included with the product.

For more information on calling OS/2 API functions from BASIC PDS
version 7.00, see Page 523 of the "Microsoft BASIC 7.0: Programmer's
Guide" included with the product.

For more information on DosQCurDisk(), see Page 547 of "Advanced OS/2
Programming," by Ray Duncan (Microsoft Press, 1989).

Note that BASIC PDS version 7.00 supports the function "CURDIR$",
which can also be used to get the currently selected drive. However,
using this method requires some string parsing, so although the code
is smaller, it may be slower.

The sample program below (GETDRIVE.BAS) reports the currently selected
drive.

To compile the program, use the following:

   bc getdrive /lp;

To link the program for BASIC 6.00 and 6.00b, use the following:

   link /nop getdrive,,,doscalls;

To link the program for BASIC 7.00, use the following:

   link /nop getdrive,,,os2;

Code Example
------------

' This declaration was taken from the include file
' BSEDOSFL.BI

DECLARE FUNCTION DosQCurDisk% (SEG CurrentDrive AS INTEGER,_
                               SEG DriveBitmap  AS LONG)

' CurrentDrive receives the current drive code (A=1, B=2,
' etc.)
' DriveBitmap receives a bitmap of each logical drive's
' availability

ErrorCode% = DosQCurDisk% (CurrentDrive%, DriveBitmap&)

IF ErrorCode% THEN
   PRINT "An error occurred, the code is";ErrorCode%
ELSE
   PRINT "The current drive is "; CHR$(CurrentDrive% + 64)
END IF

END

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