Convert a Set of to Integer

Question

As a newbie in Delphi I run into a problem with an external API. This external API expects a parameter with one or two value, I think called bitwise parameter. In Delphi this is done by a set of

The basic is an Enumeration.

TCreateImageTask = (
  citCreate = 1,
  citVerify
);

This I have put into a set of:

TCreateImageTasks = set of TCreateImageTask

In a function I fill this set with:

function TfrmMain.GetImageTask: TCreateImageTasks;
begin
    Result:=[];
    if chkCreate.checked then Include(Result, citCreate);
    if chkVerify.checked then Include(Result, citVerify);
end;

Now I have to give this Tasks to a external DLL, written in C++ The DLL expects a __int8 value. It may contain one or two TCreateImageTasks. In C++ done by:

__int8 dwOperation = 0;

   if (this->IsDlgButtonChecked(IDC_CHECK_CREATE))
   {
      dwOperation = BS_IMGTASK_CREATE;
   }

   if (this->IsDlgButtonChecked(IDC_CHECK_VERIFY))
   {
      dwOperation |= BS_IMGTASK_VERIFY;
   }

int32 res = ::CreateImage(cCreateImageParams, dwOperation);

So I have to convert my set of to an integer. I do by

function TfrmMain.SetToInt(const aSet;const Size:integer):integer;
begin
  Result := 0;
  Move(aSet, Result, Size);
end;

I call with

current task := GetImageTask;
myvar := SetToInt(currentTask, SizeOf(currentTask));

The problem I have now, that myvar is 6 when 2 values are inside the set, 2 if only create is inside the set and 4 if only verify is inside the set. That do not look right to me and the external DLL do not know this values.

Where is my fault?

You don't seem to know what "flags" are and how a byte can combine 8 bits: `2 or 4` makes `iValue= 6` and any code is still able to test against `if iValue and 2<> 0 then` . Creating an ENUM is wrong and seems to be entirely your idea, not the one of the API. — AmigoJack, Jun 29 '19 at 08:09
Sorry, the enum is out of the API. So there is still the question why the Enum citCreate is 1 but after put into an integer Is 2. I also think this is nothing about flags, because I also testes with a naked simple Delphi form without any special setting, just defaults. — ingo, Jun 29 '19 at 08:57

score 2 · Answer 1 · answered Jun 29 '19 at 08:57

I guess it works when you remove the = 1 in the declaration of TCreateImageTask?

The = 1 shifts the ordinal values by 1 giving the results you see, but is probably not what is needed. For that we need to know the values for BS_IMGTASK_CREATE and BS_IMGTASK_VERIFY.

My psychic powers tell me that BS_IMGTASK_CREATE = 1 and BS_IMGTASK_VERIFY = 2. Given that these are bit masks they correspond to the values 2^0 and 2^1. This matches the ordinal values 0 and 1.

Thus you should declare

TCreateImageTask = (citCreate, citVerify);

to map citCreate to 0 and citVerify to 1.

Luiz Vaz · Answer 2 · 2019-06-30T08:54:24.533

0

It's all about something called Bitwise Operation!

Converting a SET to LONGWORD is widely used in Delphi implementation of Windows API.

This would be what you are looking for:

How to save/load Set of Types?

This was already answered here too:

Bitwise flags in Delphi

edited Jun 30 '19 at 08:54

answered Jun 30 '19 at 07:53

Luiz Vaz

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Convert a Set of to Integer

2 Answers2