Is Record method solution or a bad hack for pointer fields?

[Mike Torrettinni 198]

I have customized INI file, so need my own record structure. So I have:

 

TINIRec = record
  Section,  Key, Value: string;
  IsSectionHeader: boolean; 
  ...
end;

And I have ComparedData array that contains pointer to TINIRec:

 

TComparedData = record
  PointerRecType: TRecType; // this identifies RecPointer as TINIRec
  RecPointer: Pointer; // Pointer to TINIRec
  ...
end;

ComparedData = TArray<TComparedData>

 

So, when ComparedData is filled with correct data from INI file, I access the content like this:

if ComparedData[x].RecPointer <> nil then
  IsINILineAHeaderLine := TINIRec(ComparedData[x].RecPointer^).IsSectionHeader;

Of course the check for nil pointer has to be everywhere...

 

So, if I set a record function like this I can avoid checking for nil record:

TComparedData = record
  PointerRecType: TRecType; // this identifies RecPointer as TINIRec
  RecPointer: Pointer; // Pointer to TINIRec
  ...
  function IsSectionHeaderLine: boolean;
end;

function TComparedData.IsSectionHeaderLine: boolean;
begin
  Result := false;
    if RecPointer <> nil then
      Result := TINIRec(RecPointer^).IsSectionHeader;
end;

 

and the call without checking for nil pointer:

IsINILineAHeaderLine := ComparedData[x].IsSectionHeader;

Is this a bad way to deal with pointers? Can this case issues later on, unexpected?

[dummzeuch 1387]

No, that's perfectly valid.

 

But why don't you decleare RecPointer as ^TIniRec and save yourself the typecasting? Or are there pointers to different types? If the latter, why do you use records instead of classes?

 

Actually I don't think this should compile:

TComparedData = record
  PointerRecType: TRecType; // this identifies RecPointer as TINIRec
  RecPointer: Pointer; // Pointer to TINIRec
  ...
  function IsSectionHeaderLine: boolean;
end;

function TComparedData.IsSectionHeaderLine: boolean;
begin
  Result := false;
    if RecPointer <> nil then
      Result := TINIRec(RecPointer^).IsSectionHeader; // <-- this should not compile as RecPointer is an untyped pointer and therefore RecPointer^ is undefined.
end;

 

Edited April 1, 2020 by dummzeuch

[Mike Torrettinni 198]

16 minutes ago, dummzeuch said:

Actually I don't think this should compile:

Hm... it compiles and runs here just fine. Or is it just luck and will fail sooner or later?

 

Maybe I should add more details: I have PINIRec = ^TINIRec; and RecPointer is set with:

 

type
  PINIRec = ^TINIRec;

var 
  vRecPointer: PINIRec;
begin
  ...
  New(vRecPointer);
  vRecPointer^ := Default(TINIRec);
  ...// here set vRecPointer values from INILine...
  ComparedData[x].RecPointer := @vRecPointer^; 

Does this make sense?

Edited April 1, 2020 by Mike Torrettinni

[Mike Torrettinni 198]

17 minutes ago, dummzeuch said:

Or are there pointers to different types?

Yes, I have other rec structures possible.

[David Heffernan 2290]

9 minutes ago, Mike Torrettinni said:

@vRecPointer^

What do you think this does? 

[Mike Torrettinni 198]

1 minute ago, David Heffernan said:

What do you think this does? 

Good catch 🙂

[David Schwartz 413]

check out BigINI from this guy, the latest (v5) is most interesting.

 

http://www.hinzen.de/delphi/index.html

 

No diffs, but it extends basic INI file managment quite nicely.

 

I've used it for years. (And added several new things.)

 

Edited April 2, 2020 by David Schwartz

[Martin Wienold 35]

This is more an FYI, instead of hardcasting a Pointer, you could use Variant Parts in Records to get the illusion of typesafety.

[Mike Torrettinni 198]

10 hours ago, David Schwartz said:

check out BigINI from this guy, the latest (v5) is most interesting.

 

http://www.hinzen.de/delphi/index.html

 

No diffs, but it extends basic INI file managment quite nicely.

 

I've used it for years. (And added several new things.)

 

Thanks, but is not really using record methods. or dealing with pointers like I do. Perhaps you were trying to point out something else?

[David Schwartz 413]

I can't tell whether you're trying to solve a programming problem, or if you're just doing mental calisthenics trying to use different programming constructs in strange ways.

 

I realize some people love using records and pointers to them in Pascal. But I spent 10+ years using c and c++ before getting into Delphi and I have always gotten confused about which side of the variable the ^ goes on and why you need to use it with a '.' because in c/c++ the '->' always goes on the right, and you never use any two of '.', '&', '*', and '->' next to each other.

 

Maybe it's the same way some people have trouble grasping the difference between how ++i and i++ work in a for loop. 

 

Suffice it to say I bet you've used pointers in Delphi more in the past month than I've used them in the past 10 years. 

 

That class DOES show some effective uses of inheritance tho.

[Fr0sT.Brutal 897]

6 hours ago, David Schwartz said:

I have always gotten confused about which side of the variable the ^ goes on and why you need to use it with a '.' because in c/c++ the '->' always goes on the right, and you never use any two of '.', '&', '*', and '->' next to each other.

It's personal. I, contrary, always stuck on C's ((foo *)bar**) etc. Pascal has different symbols for taking an address and dereferencing and it's very convenient.

[Mike Torrettinni 198]

On 4/1/2020 at 12:14 PM, dummzeuch said:

But why don't you decleare RecPointer as ^TIniRec and save yourself the typecasting? Or are there pointers to different types? If the latter, why do you use records instead of classes?

@dummzeuch I'm not sure what you are thinking here... classes instead of records? How can I use defined different classes that Pointer will point to?