Re: Reference variables in jawin?

Hello, and thanks (Morten) for the lengthy response. I have not have time
to try you suggestions until this weekend. I think I understand it but
except for one thing I am still not sure about what a "NakedByteStream"
is. I cant seem to find any information about that variable type.

Could someone give me a hint I would very grateful.

/Jonas

>> ----- Original Message -----
>> From: "Morten Andersen" <[email protected]>
>> To: <[email protected]>
>> Sent: Monday, June 21, 2004 9:27 AM
>> Subject: Re: [JAWIN] Reference variables in jawin?
>>
>>
>> > Hi Jonas
>> >
>> > Jonas Lind?n wrote:
>> > >>>
>> > >>>This is how the C++ code looks like:
>> > >>>int cbAIn( int BoardNum, int Channel, int Range, unsigned short
>> > >>>*DataValue );
>> > >>>
>> > >>
>> > >>Is the "DataValue" parameter used for returning a short value? Or is
>> it
>> > >>used for inputting a short array? So is it used as an [in] parameter
>> or
>> > >>an [out] parameter.
>> > >>
>> > >
>> > >
>> > > The DataValue is used for returning a variable of type short.
>> >
>> > Then I think something along the lines with this should do it:
>> >
>> >    FuncPtr fp = new FuncPtr("cbw32.DLL", "cbAInScan");
>> >    NakedByteStream nbs = new NakedByteStream();
>> >    LittleEndianOutputStream leos = new LittleEndianOutputStream(nbs);
>> >    leos.writeInt(boardNum);
>> >    leos.writeInt(channel);
>> >    leos.writeInt(range);
>> >
>> >    // call the function with three ints and 4 bytes allocated for
>> >    // the datavalue - see explanation of the instructionstring below
>> >    byte[] result = fp.invoke("IIIA:I:L4L4L4n4", 16, nbs, null,
>> >      ReturnFlags.CHECK_NONE);
>> >
>> >    LittleEndianInputStream leis = new LittleEndianInputStream(
>> >      new ByteArrayInputStream(result));
>> >
>> >    // return val
>> >    int retVal = leis.readInt();
>> >
>> >    // and datavalue - should perhaps not be casted to a short? - since
>> >    // unsigned short in native code?
>> >    short dataValue = (short)leis.readInt();
>> >
>> >
>> > The instruction string "IIIA:I:L4L4L4n4" should be interpreted like
>> this
>> > (on the form XXX:Y:ZZZ , where XXX is directions for [in], Y is the
>> > [retval] and ZZZ is [out]-directions) :
>> > - I: in integer (or other 4 byte value).
>> > - A: skip in instream and allocate 4 bytes on stack (yes, I know a
>> short
>> > is only 2 bytes, but on the stack the calling convention __stdcall
>> works
>> > in chunks of 4 bytes, so smaller parameters takes up 4 bytes).
>> > - L4: on the output = skip 4 bytes (we do this for all the
>> [in]-parameters).
>> > - n4: read 4 bytes of the stack and return.
>> >
>> > I know this code is not for the faint at heart, and over time the
>> Jawin
>> > Type Browser should hopefully be able to generate it for DLL's too.
>> >
>> > I am working on documenting the instruction strings too (pt. there is
>> > only this outdated documentation for this:
>> > http://jawinproject.sourceforge.net/instruction_docs.html ).
>> >
>> > Please note that I tested this code on the CVS HEAD version of Jawin,
>> > and there have been significant cleaning of the API for calling
>> > DLL-entry points since the last released version. So maybe this code
>> > does not work in the released version, if that is the case I urge you
>> to
>> > check out the CVS version and build it yourself (please see:
>> > http://jawinproject.sourceforge.net/jawindeveloper.html ).
>> >
>> > In the CVS-HEAD I also started out on some detailed information about
>> > calling DLL-entry points (see docs/jawinuserguide_dll.html in the
>> > checked out source), although it is not complete on some of the finer
>> > issues (as this is).
>> >
>> > Hope this helps you, and feel welcome to email again if you still have
>> > issues with this.
>> >
>> > Best Regards
>> > Morten
>>
>