[kingchris]

I am writing a system volume crawler.
One of the Win32 functions is

Code: Select all

Vols = string::create(256),
Count =  fileSystem_native::getLogicalDriveStrings(256, Vols),

The 256 buffer space is overkill for now I know.

The result is not a string but a series of strings separated by a null then the whole string is terminated by null null.
c:\<null>d:\<null><null>

After two days on and off looking at various ways to parse this data. result in only the C:\null being seen.
So my question is: how to replace all single nulls in this PDC Prolog wide string with say ";". The normal string::replace does not like the nulls.

Then I can parse the string using ";" as the seperator

[Martin Meyer]

Maybe there is a problem in memory::getString/2->. Because when I replaced it by my own version, it has worked out:

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    open core
 
class predicates
    getLogicalDriveStrings : (charCount BufLen, unsigned Result [out]) -> string_list Str_list.
clauses
    getLogicalDriveStrings(BufLen, Result) = getLogicalDriveStrings1(uncheckedConvert(pointer, Buf)) :-
        Buf = memory::allocStringBuffer(BufLen, memory::contextType_string),
        Result = fileSystem_native::getLogicalDriveStrings(convert(unsigned, BufLen), Buf).
 
class predicates
    getLogicalDriveStrings1 : (pointer PStr) -> string_list Str_list.
clauses
    getLogicalDriveStrings1(PStr) = if Str = "" then [] else [Str | getLogicalDriveStrings1(After)] end if :-
        %Str = memory::getString(PStr, After).
        Str = getString(PStr, After).
 
class predicates
    getString : (pointer Ptr, pointer After [out]) -> string Str.
clauses
    getString(Ptr, After) = getString1(Ptr, OutStream, After) :-
        OutStream = outputStream_string::new().
 
class predicates
    getString1 : (pointer Ptr, outputStream_string OutStream, pointer After [out]) -> string Str.
clauses
    getString1(Ptr, OutStream, After) = Str :-
        Char = memory::getChar(Ptr, AfterChar),
        if Char = '\u0000' then
            After = AfterChar,
            Str = OutStream:getString()
        else
            OutStream:write(Char),
            Str = getString1(AfterChar, OutStream, After)
        end if.
 
clauses
    run() :-
        StrList = getLogicalDriveStrings(256),
        stdIO::write(StrList).

[kingchris]

Thank you Martin Meyer. I will use it.

I had a lot of trouble converting the string to binary via direct functions or binary_outputstreams, as any conversion from strings would not read after the first null, but seeing how your method works will assist in the old learning curve.

Again. Much appreciated.

[Thomas Linder Puls]

The result you show looks like the thing we have called a msStringSeq (Microsoft String Sequence).

There are predicates in the windowsApi class for converting to and from such "sequences":

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domains
    msStringSeq = pointer.
    % @short A sequence of null (two bytes) terminated Unicode strings.
    % The sequence is ended by an empty string (same as two consecutive nulls = 4 x null).
    % @end
 
predicates
    toMsStringSeq : (string* StringList) -> msStringSeq Sequence.
    fromMsStringSeq : (msStringSeq Sequence) -> string* StringList.
    % @short Conversion between string #Sequence and list of string #StringList.
    % @end

[Martin Meyer]

ah, thank you Thomas! So, we should do it like

Code: Select all

class predicates
    getLogicalDriveStrings : (charCount BufLen, unsigned Result [out]) -> string_list Str_list.
clauses
    getLogicalDriveStrings(BufLen, Result) = windowsAPI::fromMsStringSeq(uncheckedConvert(windowsAPI::msStringSeq, Buf)) :-
        Buf = memory::allocStringBuffer(BufLen, memory::contextType_string),
        Result = fileSystem_native::getLogicalDriveStrings(convert(unsigned, BufLen), Buf).

Have I used (the outcommented) memory::getString/2-> wrong before or does it actually have a problem?

[Martin Meyer]

@Chris: For the learning curve check the implementation of fromMsStringSeq/1-> in windowsAPI.pro, it is done there more efficient than in my code.

[kingchris]

Will do