GetDrives( )

Purpose

Retrieves a list of installed drives.

*Author*	*Date of code (original)*	*Updated on*	*Date of page (original)*	*Updated on*
Bill Thoen bthoen@ctmap.com	11Jan2001	11Jan2001		29Jan2001

Restrictions on use

This module is distributed under the terms of the Lesser GNU General Public License. Restrictions on the use of this work in a commercial application or derivative work is described in the Lesser GNU General Public License page at: http://www.fsf.org/copyleft/lesser.html

Description

Returns a semi-colon delimited string of drive specifications. Calls Windows API GetLogicalDriveString32() to return the system drive strings (e.g. a:\, b:\, etc.). However the API function returns this as a single string with null byte delimiters, and MapInfo can't handle strings with null bytes in them. Instead we pass an array of integers and parse the bytes into a MapInfo semi-colon delimited string. The WinAPI declaration must be modifed as well, but this works because strings and integer arrays are mapped into the same memory space on the stack. Note that strings are one byte per character, while integers contain 4 bytes each.

External resources

Uses Windows API functions in kernel32.

Declare statement of sub_function. Include in your program. Copy/Paste if needed.

declare function GetDrives( )
as string

Returned value(s) (function only)

Semi-colon delimited string of drive specifications

Other required declare statement(s). Include in your program. Copy/Paste if needed.

declare function GetLogicalDriveString32 lib "kernel32"
   alias "GetLogicalDriveStringsA" (
   byval nBufferLength as integer,
   sBuffer() as integer
   ) as integer

MapBasic Code. Copy/Paste if needed.

function GetDrives () as string

dim nCount, nStatus as integer
dim sBuffer as string
dim sChar() as integer
dim i, n as integer

   nCount = 128
   redim sChar(nCount)

   nCount = GetLogicalDriveString32 (nCount*4, sChar)
   sBuffer = ""
   for i = 1 to nCount\4
      'Convert 4 bytes of integer into 4 bytes of string.
      'Note that byte order for integers is reversed
      'from byte-order of strings.
      n = (sChar(i) \ 256^0) mod 256
      if n = 0 then n = asc(";") end if
      sBuffer = sBuffer + chr$(n)
      n = (sChar(i) \ 256^1) mod 256
      if n = 0 then n = asc(";") end if
      sBuffer = sBuffer + chr$(n)
      n = (sChar(i) \ 256^2) mod 256
      if n = 0 then n = asc(";") end if
      sBuffer = sBuffer + chr$(n)
      n = (sChar(i) \ 256^3) mod 256
      if n = 0 then n = asc(";") end if
      sBuffer = sBuffer + chr$(n)
   next
   GetDrives = UCase$(sBuffer)
end function

Availability for download

Dir_File.zip

Example

dim sDrives as string

sDrives = GetDrives()
sDrives might now contain "A:\;C:\;D:\"

Comments

See also

GetFilenames
GetDir