I want to store this string expression:
oField.displayname+'='+varTostr(fieldbyname(ofield.fieldame).value)
where ofield is TField of dataset in TComponent.Tag. How can I do this?
I am using FreePascal.
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Please add what you have tried and what is the expected output.samhita– samhita2024-12-01 17:44:02 +00:00Commented Dec 1, 2024 at 17:44
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2 Answers
The Tag field of a TComponent is of type PtrInt, which is large enough to store a pointer, including the memory address of a string. You can use the Tag to store the address of a dynamically allocated string.
procedure TForm1.FormCreate(Sender: TObject);
var
MyString: PChar;
begin
MyString := StrAlloc(100);
StrPCopy(MyString, 'Hello, Free Pascal!');
Label1.Tag := PtrInt(MyString);
Edit1.Text := PChar(Label1.Tag);
StrDispose(PChar(Label1.Tag));
end;
Ensure that the memory is always properly deallocated to avoid leaks or dangling pointers
Comments
You asked this same question in the FreePascal forum, so I'll post here the same example I gave you there.
https://forum.lazarus.freepascal.org/index.php/topic,69500.msg539938.html#msg539938
// to store a new string... var tag: Pointer; tag := nil; string(tag) := 'yourstringhere'; TButton.Tag := PtrInt(tag);// to retrieve the stored string... var tag: Pointer; tag := Pointer(TButton.Tag); Somestring := string(tag);// to update the stored string... var tag: Pointer; tag := Pointer(TButton.Tag); string(tag) := 'yourstringhere'; TButton.Tag := PtrInt(tag);// to release the stored string when done using the Tag... var tag: Pointer; tag := Pointer(TButton.Tag); string(tag) := ''; TButton.Tag := 0;[/code]