Update/Delete Record items in a Stream

[mandoza]

Hi every one , i save my records into a stream i can read them back , but what i want is to be able to update or delete one of my records item then save back .
please how to do that . thank you

Delphi-Quellcode:

Tmyrecord = Record
  Firstname : string ; 
  LastName:string;
  ID : integer ;  
end;

....

procedure WriteIntegerToStream(Stream: TStream; Value: Integer);
begin
  Stream.WriteBuffer(Value, Sizeof(Value));
end;

procedure WriteStringToStream(Stream: TStream; const Value: String);
var
  S: UTF8String;
  Len: Integer;
begin
  S := UTF8String(Value);
  Len := Length(S);
  Stream.WriteBuffer(Len, Sizeof(Len));
  Stream.WriteBuffer(PAnsiChar(S)^, Len);
end;

function ReadIntegerFromStream(Stream: TStream): Integer;
begin
  Stream.ReadBuffer(Result, Sizeof(Result));
end;

function ReadStringFromStream(Stream: TStream): String;
var
  S: UTF8String;
  Len: Integer;
begin
  Stream.ReadBuffer(Len, Sizeof(Len));
  SetLength(S, Len);
  Stream.ReadBuffer(PAnsiChar(S)^, Len);
  Result := String(S);
end;

Procedure SaveToStream();
var 
  SavingStream: TFileStream;
  i, j: Integer;
  myRec:Tmyrecord;
begin
  SavingStream := TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
  try 
      WriteStringToStream(SavingStream, myRec.Firstname);
      WriteStringToStream(SavingStream, myRec.LastName);
      WriteIntegerToStream(SavingStream, myRec.ID);
  finally
    SavingStream.Free;
  end;
end;

procedure LoadFromStream()
var 
  LoadingStream: TFileStream;
  i, j: Integer;
  myRec:Tmyrecord;
begin
  LoadingStream := TFileStream.Create('SAVE.test', fmOpenRead or fmShareDenyWrite);
  try
    
      myRec.Firstname:= ReadStringFromStream(LoadingStream);
      myRec.LastName := ReadStringFromStream(LoadingStream);
      myRec.ID := ReadIntegerFromStream(LoadingStream);
     
  finally
    LoadingStream.Free;
  end;
end;

procedure UpdateMyRecLastName(NewLastName:string);
var 
  LoadingStream: TFileStream;
  i, j: Integer;
  myRec:Tmyrecord;
begin
  SavingStream := TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
  try 
      
       myRec.LastName:=NewLastName;
      
      {
      Here how to update myRec.LastName value in the LoadingStream
      }
    
  finally
    SavingStream.Free;
  end;
end;

procedure DeleteMyRecLastName();
var 
  LoadingStream: TFileStream;
  i, j: Integer;
  myRec:Tmyrecord;
begin
  SavingStream := TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
  try 
      {
      Here how to Delete myRec.LastName value in the LoadingStream
      }
    
  finally
    SavingStream.Free;
  end;
end;

[DeddyH]

Why not define a specialized list?

Delphi-Quellcode:

uses ..., System.Generics.Collections;

type
  TMyRecList = class(TList<Tmyrecord>)
  public
    procedure LoadFromFile(const Filename: string);
    procedure SaveToFile(const Filename: string);
  end;

[Der schöne Günther]

And then your next steps will probably be writing UpdateFirstName or UpdateId methods.

Why not

1. Load your data from stream
2. Alter them in memory
3. Save everything again

It looks like you already have everything you need.

[mandoza]

Zitat von Der schöne Günther:

And then your next steps will probably be writing UpdateFirstName or UpdateId methods.

Why not

1. Load your data from stream
2. Alter them in memory
3. Save everything again

It looks like you already have everything you need.

How to do that please ?

[mandoza]

what i wanted is to be able to :
1- Load that record item from Stream ( Done )
2- Update that record item value ( Done )
3- Update that modified record item value in the Stream , that means Replace that OLD item value with this New Value then save again ( HOW TO )

[Der schöne Günther]

Can you post your real code? Your current LoadFromStream() and SaveToStream() appear to be testing routines because they contain syntax errors and, in their current form, do not make sense:

In LoadFromStream() you load your data into a local variable myRec . After that, your procedure ends and myRec is gone. You can inspect myRec in the debugger, but in the end, this method accomplishes nothing.

"Real code" would, for example, take an instance of TMyrecord and a filename as parameters for LoadFromStream() and SaveToStream()

[mandoza]

Zitat von DeddyH:

Why not define a specialized list?

Delphi-Quellcode:

uses ..., System.Generics.Collections;

type
  TMyRecList = class(TList<Tmyrecord>)
  public
    procedure LoadFromFile(const Filename: string);
    procedure SaveToFile(const Filename: string);
  end;

Thank you , but what i wanted is to be able to update / delete items from my record then save / read again .
please read the

Delphi-Quellcode:

procedure UpdateMyRecLastName(NewLastName:string);
var 
  LoadingStream: TFileStream;
  i, j: Integer;
  myRec:Tmyrecord;
begin
  SavingStream := TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
  try 
      
       myRec.LastName:=NewLastName;
      
      {
     Here how to update myRec.LastName value in the LoadingStream
      }
    
  finally
    SavingStream.Free;
  end;
end;

procedure DeleteMyRecLastName();
var 
  LoadingStream: TFileStream;
  i, j: Integer;
  myRec:Tmyrecord;
begin
  SavingStream := TFileStream.Create('SAVE.test', fmCreate or fmOpenWrite or fmShareDenyWrite);
  try 
      {
     Here how to Delete myRec.LastName value in the LoadingStream
      }
    
  finally
    SavingStream.Free;
  end;
end;

[mandoza]

So many thanks for all your great efforts .