Type conversion to DWord(s) 2

[djjd47130]

Some API functions which I'm calling require some DWORD parameters. Some of those parameters allow multiple values, such as...

CONST_ONE or CONST_TWO or CONST_THREE

I'm trying to wrap this into a component with some properties, such as...

type
  TCon = (cOne, cTwo, cThree);
  TCons = set of TCon;
  ...
procedure DoSomething;
var
  C: TCons;
begin
  ...
  C:= [cOne, cThree];
  ...
end;

and somehow, that needs to be converted to...

CONST_ONE or CONST_THREE

Any ideas?


JD Solutions

 

[whosrdaddy]

Don't see what's the point here.
constants are there for a reason, no need to add some sets into the mix.

what you can do (although pointless):

const
 CONST_ONE = 1;
 CONST_TWO = 2;
 CONST_THREE = 4;
 CONST_ONE_OR_THREE = CONST_ONE or CONST_THREE

meh, don't do it

/Daddy


-----------------------------------------------------
What You See Is What You Get
Never underestimate tha powah of tha google!

 

[Griffyn]

Agreed. Constants should be self documenting, whereas your approach will likely obfuscate the code.

 

[Glenn9999]

Yes you're making it more complicated than it needs to be. You'd have to have code to explicitly make the conversion (eg a long string of if statements) if you were to proceed with this.

It is not possible for anyone to acknowledge truth when their salary depends on them not doing it.

 

[djjd47130]

You're missing the whole point. I'm building a Component. The properties of this component will show in the Object Inspector. Such a property is like the Font Style, or the Anchors of a control. This is the same thing, it will be an expanding property with a number of true/false values. I can't do that with constants, only with Sets.

JD Solutions

 

[djjd47130]

I'll be a little more specific with what I'm doing...

This component I'm building will be listing various resources/devices (otherwise computers) on the network. There are two API functions for this:

{$EXTERNALSYM WNetOpenEnum}
function WNetOpenEnum(dwScope, dwType, dwUsage: DWORD;
  lpNetResource: PNetResource; var lphEnum: THandle): DWORD; stdcall;

{$EXTERNALSYM WNetEnumResource}
function WNetEnumResource(hEnum: THandle; var lpcCount: DWORD;
  lpBuffer: Pointer; var lpBufferSize: DWORD): DWORD; stdcall;

for example, WNetOpenEnum can have multiple values for dwType and dwUsage.

I already made functions which convert this, but I can't avoid having one *false* value in the set of DWord's...

function NetResourceTypesToDWord(Types: TNetResourceTypes): DWORD;
begin
  if nrAny in Types then
    Result:= Result or RESOURCETYPE_ANY;
  if nrDisk in Types then
    Result:= Result or RESOURCETYPE_DISK;
  if nrPrint in Types then
    Result:= Result or RESOURCETYPE_PRINT;
  if nrReserved in Types then
    Result:= Result or RESOURCETYPE_RESERVED;
end;

function NetUsagesToDWord(Usages: TNetUsages): DWORD;
begin
  if ruConnectable in Usages then
    Result:= Result or RESOURCEUSAGE_CONNECTABLE;
  if ruContainer in Usages then
    Result:= Result or RESOURCEUSAGE_CONTAINER;
  if ruNoLocalDevice in Usages then
    Result:= Result or RESOURCEUSAGE_NOLOCALDEVICE;
  if ruSibling in Usages then
    Result:= Result or RESOURCEUSAGE_SIBLING;
  if ruAttached in Usages then
    Result:= Result or RESOURCEUSAGE_ATTACHED;
  if ruAll in Usages then
    Result:= Result or RESOURCEUSAGE_ALL;
  if ruReserved in Usages then
    Result:= Result or RESOURCEUSAGE_RESERVED;
end;

function NetDisplayTypesToDWord(Types: TNetDisplayTypes): DWORD;   
begin
  if ndGeneric in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_GENERIC;
  if ndDomain in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_DOMAIN;
  if ndServer in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_SERVER;
  if ndShare in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_SHARE;
  if ndFile in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_FILE;
  if ndGroup in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_GROUP;
  if ndNetwork in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_NETWORK;
  if ndRoot in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_ROOT;
  if ndShareAdmin in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_SHAREADMIN;
  if ndDirectory in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_DIRECTORY;
  if ndTree in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_TREE;
  if ndNDSContainer in Types then
    Result:= Result or RESOURCEDISPLAYTYPE_NDSCONTAINER;
end;

Like I mentioned, these are properties of this component...

JD Solutions

 

[whosrdaddy]

ok, Now I understand, thanks.

normally you could get away with:

 MyDword := LongWord(MySet);

/Daddy

-----------------------------------------------------
What You See Is What You Get
Never underestimate tha powah of tha google!

 

[djjd47130]

Thanks whosrdaddy, I'll give that a check. Otherwise, I think I could initialize the result to -1, then check if the result is -1 then directly assign the result to the constant, or if the result is not -1, then add it with 'or'. But, that would make the code 5 times as big as it already is...

function NetResourceTypesToDWord(Types: TNetResourceTypes): DWORD;
begin
  Result:= DWord(-1);
  if nrAny in Types then begin
    if Result = -1 then
      Result:= RESOURCETYPE_ANY
    else
      Result:= Result or RESOURCETYPE_ANY;
  end;
  if nrDisk in Types then begin
    if Result = -1 then
      Result:= RESOURCETYPE_DISK
    else
      Result:= Result or RESOURCETYPE_DISK;
  end;
end;

Haven't given it a try yet, but it should work. I just hate to put so much code for such a simple task. I hope I can figure out whosrdaddy's suggestion with...

MyDword := LongWord(MySet);

JD Solutions

 

[whosrdaddy]

Result := Longword(Types); ???

no need to write a function for that...

/Daddy

-----------------------------------------------------
What You See Is What You Get
Never underestimate tha powah of tha google!

 

[djjd47130]

But how does it know that nrReserved represents the constant RESOURCETYPE_RESERVED?

This is how I have it defined:

type
  TNetResourceType = (nrAny, nrDisk, nrPrint, nrReserved);
  TNetResourceTypes = set of TNetResourceType;

And in the Windows unit (at least for Delphi 7) on line #27,478 the constant RESOURCETYPE_RESERVED is declared.

JD Solutions

 

[whosrdaddy]

you must build the set the way the constants are defined.

a set uses a 16 bytes, so it can represent 256 bits.

using your example:

 look in the windows.pas file and search for the constants:

  RESOURCETYPE_ANY = 0;
  RESOURCETYPE_DISK = 1;
  RESOURCETYPE_PRINT = 2;
  RESOURCETYPE_RESERVED = 8;

as you can see these values represent bits
RESOURCETYPE_DISK = bit 0 (2^0)
RESOURCETYPE_PRINT = bit 1 (2^1)
RESOURCETYPE_RESERVED = bit 3 (2^3)

bit 2 is not documented by the API (for some reason)

 
how to implement:
TNetResourceType = (nrDisk, nrPrint, nrReserved=3);
// or (nrDisk, nrPrint, nrDummy1, nrReserved) for delphi versions lower dan 6

nrAny represents 0 so don't need it

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, TypInfo;

type
  TNetResourceType = (nrDisk, nrPrint, nrReserved=3);
  TNetResourceTypes = set of TNetResourceType;
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function Set2DWord(AType: PTypeInfo; const ASet): DWord;
begin
 Result := 0;
 case GetTypeData(AType)^.OrdType of
  otSByte, otUByte: Result := Byte(ASet);
  otSWord, otUWord: Result := Word(ASet);
  otSLong, otULong: Result := DWord(ASet);
 end;
end;


procedure TForm1.Button1Click(Sender: TObject);

var MySet : TNetResourceTypes;
begin
 MySet := [nrDisk, nrPrint, nrReserved];
 ShowMessage(InttoStr(Set2DWord(TypeInfo(TNetResourceTypes), MySet)));
end;

end.

play with the code and see if it makes sense to you...

/Daddy


-----------------------------------------------------
What You See Is What You Get
Never underestimate tha powah of tha google!

 

[djjd47130]

adding that nrReserved=3 made me understand better. However, then I saw that function you made Set2DWord and got even more confused, especially with the pointer reference. I will play around with it and hopefully will make it work, thanks.

JD Solutions

 

[djjd47130]

Bad news, that idea of assigning the values in the declaration won't work. Delphi won't allow using such types as published properties of a component.

I know ActiveX stuff has some way of converting constants to publishable properties. I'll probably wind up investigating that, because when I convert a component to an ActiveX component, it somehow converts those types of properties to something similar.

JD Solutions