How To Get Default Directories Of Drives In QB64

Question

I have been using the following code to get the default directories of all drives, however I don't want to use _CWD$

is there a more efficient way to do this?

REM get default directory of drives.
ON ERROR GOTO ErrSub
FOR D = 1 TO 26
    D$ = CHR$(D + 64) + ":"
    DataError = 0
    CHDIR D$
    IF DataError = 0 THEN
        PRINT _CWD$
    END IF
NEXT
END

ErrSub:
DataError = ERR
RESUME NEXT

Why don't you want to use `_CWD$` and what about it is not efficient enough? — BdR, Sep 06 '16 at 19:49
My quadcore won't run recent QB64 dirty builds, only an old dialect of QB64 which does not support _CWD$ and it's not efficient to error bounce when there's only one error routine and 1,000s line of code. — eoredson, Sep 07 '16 at 01:16

score 2 · Answer 1 · answered Sep 11 '16 at 17:10

For the _CWD$ replacement, you can do this:

' Need to use DECLARE LIBRARY for the C function getcwd(string, stringSize).
DECLARE LIBRARY ""
    FUNCTION getcwd$ (buffer$, BYVAL buflen)
END DECLARE

' Wrapper function for making usage of getcwd$ more BASIC-like.
DECLARE FUNCTION qb64cwd$ ()

' Print the current working directory.
PRINT qb64cwd$

FUNCTION qb64cwd$ ()
    ' 32768 characters should be more than large enough on any OS.
    REDIM s AS STRING * 32768
    qb64cwd$ = getcwd$(s, 32768)
END FUNCTION

While you don't really need to have a wrapper function, the C function requires you to pass a string with a sufficient amount of writable memory. That is, getcwd doesn't allocate memory. It expects you to pass a sufficient amount of memory, and QB64's dynamically sized STRING type won't do that, so a wrapper is used to create a fixed-length string of sufficient size and pass that to the function. wrapper does that well enough to suffice in most cases. Note that this should also work on OS X and Linux (and pretty much any other POSIX-like system that QB64 runs on, possibly even including Android). I haven't tested on those systems, but it should work since getcwd is a POSIX function.

What happens when that number isn't large enough? Well, QB64 doesn't allow arrays to be passed to library functions, and you can't use STRING * variable unless variable is CONST variable = .... That means you can't enlarge the string and try again. You should probably raise an error if that happens to to tell you that something went wrong (e.g. ERROR 75).

That's exactly what I was looking for! I am using ASCIIZ as string * 260 for the buffer instead. — eoredson, Sep 12 '16 at 00:48

score 1 · Answer 2 · answered Sep 10 '16 at 01:03

1

One way to get default directories of all drives in QB64 without error trapping:

REM get default directory of drives.
FOR D = 65 TO 90
    D$ = CHR$(D) + ":"
    IF _DIREXISTS(D$) THEN
        CHDIR D$
        PRINT _CWD$
    END IF
NEXT
END

answered Sep 10 '16 at 01:03

eoredson

1,167
2
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Still can't replicate the _CWD$ function yet. – eoredson Sep 10 '16 at 01:04
Still might prompt to insert media for devices (not cd-rom). – eoredson Sep 21 '16 at 21:14

score 0 · Accepted Answer · answered Dec 30 '16 at 02:28

Have also noticed the default directory is not always the directory where a file was started from, so, here is a sample describing each:

' directory file was loaded from
PRINT _CWD$

' declare external libraries.
DECLARE DYNAMIC LIBRARY "kernel32"
    FUNCTION SetCurrentDirectoryA% (f$)
END DECLARE

' force default path
x$ = _STARTDIR$
f$ = x$ + CHR$(0)
x = SetCurrentDirectoryA(f$)

' directory where user is in dos
PRINT _CWD$

How To Get Default Directories Of Drives In QB64

3 Answers3