Saving Files with custom Records containing Arrays of Arrays
lazarus / 8-Other

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Fr0zn S0ul · 2009-06-29 07:41

Just having a little problem with saving a file that contains a custom
record with an array of an array (seen below).
The items read properly before the save, but when I try to read them
back from the file the secondary array is empty.

These are my custom records.
There are multiple TJobs used since this is a database system.
There are multiple products within each TJob because their will be
both different items used during each job and a quantity of labour:
Code: [Select]TProduct = record
  Name: String;
  Index: integer;
  Price: Extended;
end;

TJob = record
  JCustomer: TCustomer;
  JNum: Integer;
  JSubtotal, JGST, JTotal: Extended;
  JDescription: String;
  JDate: TDate;
  JQuantity: Array of Integer;
  JProducts: Array of TProduct;
end;                            

var
  Jobs: Array of TJob;              

Gathering data from the form and saving to file:
Code: [Select]//increase number of existing TJobs by one to save the
new data in.
  SetLength(Jobs, Length(Jobs) + 1);
  SetLength(Jobs[High(Jobs)].JProducts, Length(Product));
  SetLength(Jobs[High(Jobs)].JQuantity, Length(Product));
//find which customer is being saved and gather the data.
  for i := 0 to High(Customer) do
    if Customer[i].LastName + ', ' + Customer[i].FirstName =
ComboBox1.Text then begin
      Jobs[High(Jobs)].JCustomer := Customer[i];
      Break;
    end;
//gain data from the text fields on the form and save them to the new
TJob
  with Jobs[High(Jobs)] do begin
    JDate := StrToDate(Edit2.Text);
    JDescription := Edit4.Text;
    JNum := StrToInt(Edit1.Text);
    JSubtotal := StrToFloat(Label8.Caption);
    JGST := StrToFloat(Label9.Caption);
    JTotal := StrToFloat(Label10.Caption);
  end;
//for each product created, assign it to the TJob
  for i := 0 to High(Product) do
    with Jobs[High(Jobs)] do begin
      JQuantity[i] := Quantity[i].Value;
      JProducts[i].Name := Product[i].Text;
      JProducts[i].Index := Product[i].ItemIndex;
      JProducts[i].Price := StrToFloat(UnitPrice[i].Text);
//write to file
  AssignFile(IFile, 'IData.DAT');
  ReWrite(IFile);
  for i := 0 to High(Jobs) do
    Write(IFile, Jobs[i]);
  CloseFile(IFile);                                     

Loading from the file and restoring to the form:
Code: [Select]//reset and load the job list from file
 SetLength(Jobs, 0);
  AssignFile(IFile, 'IData.DAT');
  Reset(IFile);
  i3 := 0;
  While not eof(IFile) do begin
    SetLength(Jobs, i3 + 1);
    Read(IFile, Jobs[i3]);
    i3 := i3 + 1;
  end;
  CloseFile(IFile);
//select which element of the job array to load
  i3 := StrToInt(InputBox('Job Num', 'Enter the job number', ''));
//load the customers name into the form - works
  ComboBox1.Text := Jobs[i3].JCustomer.LastName + ', ' +
Jobs[i3].JCustomer.FirstName;
//load job number - works
  Edit1.Text := IntToStr(Jobs[i3].JNum);
//load the date - works when saving as a TDate (not as a string
though?)
  Edit2.Text := DateToStr(Jobs[i3].JDate);
//load description of job - works
  Edit4.Text := Jobs[i3].JDescription;

//now the problems being
  for i2 := 0 to High(Jobs[i3].JProducts) do begin
//create a new line for each product, works.
    AddLine(Button1);
//the name is loading as either '' or as random strings such as
[][][]1[][][][][2[][][][][]3[][][][][][][][][][][]2 so there is a
problem saving this?
    Product[i2].Text := Jobs[i3].JProducts[i2].Name;
//not loading
    Product[i2].ItemIndex := Jobs[i3].JProducts[i2].Index;
//stays at 0 most the time, occasionally set itself to the maximum of
1000 (?)
    Quantity[i2].Value := Jobs[i3].JQuantity[i2];
//Didn't actually save these since it can be calculated through a
different procedure
    UnitPrice[i2].Text := FloatToStrF(Jobs[i3].JProducts[i2].Price,
ffFixed, 1, 2);
    LinePrice[i2].Text := FloatToStrF(StrToFloat(UnitPrice[i2].Text) *
Quantity[i2].Value, ffFixed, 1, 2);
  end;                                  

So the problem is with the loading (or saving) of the TProduct array
within the TJob.

An error I seem to get occasionally (or whenever it actually displays
one) is
'Invalid floating point operation'.
I have not been able to find a lot of info on this problem or locate
its source yet. Any help or knowledge would be greatly appreciated!

Also if any of you know how to read records from .dat files and such
that'd be very useful

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Vincent Snijders · 2009-06-29 08:19

You cannot safe records with dynamic arrays (and ansistrings) to disk
directly, because they contain pointers, which are meaningless if you
read the records back. Reading records you did, can only work for
fixed length records, and you expect a variable length record to be
stored.

If you really want to hand code saving to file and not use a database
like tdbf or sqlite, I recommend to use a TStream (e.g. TFileStream),
to read/write the individual data fields to file.

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Fr0zn S0ul · 2009-06-29 08:20

OK thank you very much for this, will look into it