[SOLVED] Work with array property
lazarus / 64-FPC development

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Okoba · 2026-01-28 17:27

Hello,
In this sample can you tell me how can I correctly get length of the
array, and add or delete elements to it? I can cast it to Integer
array but I like to know the generic way that works for all element
types.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
Project1;{$mode objfpc}{$H+}{$M+}{$RTTI EXPLICIT 
 PROPERTIES([vcPrivate,vcProtected,vcPublic,vcPublished]) 
 FIELDS([vcPrivate,vcProtected,vcPublic,vcPublished]) 
 METHODS([vcPrivate,vcProtected,vcPublic,vcPublished])}uses 
TypInfo; type  TTest = record    A: array of integer;  end;var  T:
TTest;  FieldTable: PExtendedFieldInfoTable;  FieldCount, I:
Integer;begin  T.A := [1, 2, 3];  FieldCount :=
GetFieldList(TypeInfo(TTest), FieldTable);  for I := 0 to FieldCount -
1 do    with FieldTable^[I]^ do    begin      if Name^ = 'A' then    
begin      How to get the array length?      How to add another item
to the array?      end;    end;  ReadLn;end.

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ALLIGATOR · 2026-01-28 18:52

It's scary, but it works

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
Project1;{$mode objfpc}{$H+}{$M+}{$RTTI EXPLICIT 
 PROPERTIES([vcPrivate,vcProtected,vcPublic,vcPublished]) 
 FIELDS([vcPrivate,vcProtected,vcPublic,vcPublished]) 
 METHODS([vcPrivate,vcProtected,vcPublic,vcPublished])}uses 
TypInfo; type  TTest = record    A: array of UInt64;  end;var  T:
TTest;  FieldTable: PExtendedFieldInfoTable;  FieldCount, I: Integer; 
newlen: SizeInt = 33;begin  T.A := [1, 2, 3];  FieldCount :=
GetFieldList(TypeInfo(TTest), FieldTable);  for I := 0 to FieldCount -
1 do    if FieldTable^[I]^.Name^ = 'A' then    begin      //How to get
the array length?     
WriteLn(DynArrayBounds(@PByte(@T)[FieldTable^[I]^.FieldOffset],
FieldTable^[I]^.FieldType^)[0]+1);       //How to add another item to
the array?     
DynArraySetLength(PPointer(@PByte(@T)[FieldTable^[I]^.FieldOffset])^,
FieldTable^[I]^.FieldType^, 1, @newlen);    end;  
WriteLn(Length(T.A));  ReadLn;end.

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Okoba · 2026-01-29 07:20

Thank you!
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
PPointer(@PByte(@T)[FieldTable^[I]^.FieldOffset])^This part is
confusing? it is pointer of the array property?
How can i set the newly added element dynamically depending on the
array element type? like if it is integer set it to 1 and if string
set to '1'?

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ALLIGATOR · 2026-01-29 08:10

Something like that, but I'm starting to dislike this code more and
more

Besides, I'm still confused as to why I get the array element type
this way. I originally wrote it differently, but it didn't work...

And this worked, but I don't have time to figure it out yet, so I'll
leave it as is

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
Project1;{$mode objfpc}{$H+}{$M+}{$RTTI EXPLICIT 
 PROPERTIES([vcPrivate,vcProtected,vcPublic,vcPublished]) 
 FIELDS([vcPrivate,vcProtected,vcPublic,vcPublished]) 
 METHODS([vcPrivate,vcProtected,vcPublic,vcPublished])}uses 
TypInfo; type  TTest = record    A: array of Integer;  end;var  T:
TTest;  FieldTable: PExtendedFieldInfoTable;  FieldCount, I: Integer; 
newlen: SizeInt = 33;  s: string;  ptd: PTypeData;begin  T.A := [1, 2,
3];  FieldCount := GetFieldList(TypeInfo(TTest), FieldTable);  for I
:= 0 to FieldCount - 1 do    if FieldTable^[I]^.Name^ = 'A' then   
begin      //How to get the array length?     
WriteLn(DynArrayBounds(@PByte(@T)[FieldTable^[I]^.FieldOffset],
FieldTable^[I]^.FieldType^)[0]+1);       //How to add another item to
the array?     
DynArraySetLength(PPointer(@PByte(@T)[FieldTable^[I]^.FieldOffset])^,
FieldTable^[I]^.FieldType^, 1, @newlen);       WriteStr(s,
FieldTable^[I]^.FieldType^^.Kind);      WriteLn(s);       case
FieldTable^[I]^.FieldType^^.Kind of        tkUnknown:;       
tkInteger:;        tkChar:;        tkEnumeration:;        tkFloat:;  
    tkSet:;        tkMethod:;        tkSString:;        tkLString:;  
    tkAString:;        tkWString:;        tkVariant:;       
tkArray:;        tkRecord:;        tkInterface:;        tkClass:;    
  tkObject:;        tkWChar:;        tkBool:;        tkInt64:;       
tkQWord:;        tkDynArray:        begin         
ptd:=GetTypeData(FieldTable^[I]^.FieldType^);           case
ptd^.OrdType of            otSLong:
PInteger(PPointer(@PByte(@T)[FieldTable^[I]^.FieldOffset])^)[3]:=44; 
       end;         end;        tkInterfaceRaw:;        tkProcVar:;  
    tkUString:;        tkUChar:;        tkHelper:;        tkFile:;   
   tkClassRef:;        tkPointer:;      end;     end;  
WriteLn(Length(T.A));  WriteLn(T.A[0]);  WriteLn(T.A[1]); 
WriteLn(T.A[2]);  WriteLn(T.A[3]);  WriteLn(T.A[4]);  ReadLn;end.

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PascalDragon · 2026-01-29 20:02

Quote from: Okoba on January 29, 2026, 08:20:04 amCode: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
PPointer(@PByte(@T)[FieldTable^[I]^.FieldOffset])^This part is
confusing? it is pointer of the array property?
It's a field, not a property.