Saving records

[ginnix 2]

Hi All,

 

I  have this record Type

 type
   TCustomer= record
     CompanyName:String[255];
     SpotsAllocated:Integer;
     LicensePlates:String[255];
     Parked:string[255];
   end;
   var
   myFile:File of TCustomer;
   CompanyDataBase:array[1..100] of TCustomer;
 

 

 

 

To save the information once the record is populated I use

AssignFile(F, 'c:\tmp\test.txt');
  Rewrite(F);
  for i := Low(CompanyDataBase) to High(CompanyDataBase) do
   Write(F, CompanyDataBase);
   CloseFile(F);

 

This seems to work, I can see the data in the text file.  

 

My problem is reading this back. I am stuck on how to read the data back into the program.

 

 

Any tips appreciated.

 

Thanks

 

 

 

 

[Dave Novo 48]

Hello,

This is a very old school way of saving data. Probably from Pascal in 1980. You should not do it this way any longer. I would do something as follows (note, I am writing this without testing syntax)

 

TCustomer= record
     CompanyName:String[255];
     SpotsAllocated:Integer;
     LicensePlates:String[255];
     Parked:string[255];
     procedure SaveToStream(aStream:TStream);
     procedure LoadFromStream(aStream:TStream)
   end;


TCustomerArr=array of TCustomer;

TCustomerArrHelper=record helper for TCustomerArr
  procedure SaveToStream(aStream:TStream)
  procedure LoadFromSTream(aSTream:TStream)
  procedure SaveToFile(const aFileName:string);

end;


procedure TCustomer.SaveToSTream(aStream:TStream);
var
  ver:integer;
begin
   ver:=1; // always save a version number in case you change the record format in the future
   aStream.WriteBuffer(ver,sizeof(ver));
  // call aStream.Write for other fields

end;

procedure TCustomer.LoadFromSTream(aStream:TStream);
var
   ver:integer;
begin
   aStream.ReadBuffer(ver,sizeof(ver));
  if ver<>1 then raise Exception.Craete('Version mismatch');
  aSTream.ReadBuffer();// one readbuffer to match the writes above
end;


procedure TCustomerArrHelper.SaveToStream(aStream:TSTream);
var
  ver:integer;
  cust:TCustomer;
begin
   ver:=1;
   aStream.WriteBuffer(ver,sizeof(ver));
   myLen:=Length(self);
   sTream.WriteBuffer(myLen,sizeof(mylen)); // save the length, you will use the length when reading in to allocate the array size
   for cust in self do
      cust.SaveToSTream(aStream);
end



procedure TCustomerArrHelper.LoadFromStream(aStream:TSTream);
var
  ver:integer;
  myLen:integer;
  cust:TCustomer;
begin

   aStream.ReadBuffer(ver,sizeof(ver));
   if ver<>1 then raise Exception.Craete('Version mismatch');

   aSTream.ReadBuffer(myLen,sizeof(mylen));
   SetLength(self,myLen)

   for cust in self do
      cust.LoadFromSTream(aStream);
end


procedure TCustomerArrHelper.SaveToFile(const aFileName:string);
var
  f:TFileStream;
begin
  f:=TFileStream.Create(aFileName,fmCreate);
  try
    someCustArr.SaveToSTream(f);
  finally
    f.free
  end
end

 

 

 

Edited July 15, 2022 by Dave Novo

[PeterBelow 218]

13 hours ago, ginnix said:

AssignFile(F, 'c:\tmp\test.txt');
  Rewrite(F);
  for i := Low(CompanyDataBase) to High(CompanyDataBase) do
   Write(F, CompanyDataBase);
   CloseFile(F);

Have you tried the obvious:

AssignFile(F, 'c:\tmp\test.txt');
Reset(F);
for i := Low(CompanyDataBase) to High(CompanyDataBase) do
   Read(F, CompanyDataBase[I]);
CloseFile(F); 

 

[Lajos Juhász 238]

39 minutes ago, PeterBelow said:

for i := Low(CompanyDataBase) to High(CompanyDataBase) do

As far as I remember this should be

 

i:=0;

SetLength(CompanyDataBase, FileSize(f))

while not eof(f) do

begin

  Read(f, CompanyDataBase);

  inc(i);

end;

 

Last time I wrote a code like this was in Pascal. (Btw. to be on the safe side you should also define the record as packed).