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How to Access fields by number in a record

Posted on 2008-10-26
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Last Modified: 2011-10-03
I need to be access the fields in a record sequentialy and to find the field type.

type
  STran = record
    TranType :array[0..1] of char;
    AccountRef :array[0..7] of char;
    NomCode :array[0..7] of char;
    DeptNo :integer;
    TransDate :array[0..9] of char;
    Net :currency;
    :
    :
  end;

example in Psudo Code
    for x:= 0 to STran.FIELDCOUNT -1 do
    begin
      case stTran.FIELDBYNUMBER[x].FIELDTYPE of
      String : //  process the value of thid field as a string;

      Currency ://
      Integer : //
      end; // end case

  Any suggestion on how to achiev this.

Thanks in advance
Alan
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Question by:alanjbrown
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14 Comments
 
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Expert Comment

by:2266180
ID: 22808014
you can't.

but you could, if you would use a class instead of a record and make those record member to be published properties in the class. you will use RTTI for this (start from here: http://delphi.about.com/od/oopindelphi/a/delphirtti.htm )
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Author Comment

by:alanjbrown
ID: 22808542
Are you able to give me a more specific example of how RTTI can be applied to my question?
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Expert Comment

by:2266180
ID: 22808584
are you willing to use a class instead of a record? I dont' want to waste my time if you do not ;)
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LVL 37

Expert Comment

by:Geert Gruwez
ID: 22808633
you could access them with a function or 2 you define
but for every new type of record ... you would have to create new functions

or use variant







type
  STranFieldCount = 10;
 
function STranField(Rec: STran; Index: Integer): Variant;
begin
  case Index of 
    0: Result := Rec.TranType;
    1: Result := Rec.AccountRef;
    2: Result := Rec.NomCode;
    3: Result := Rec.DeptNo;
    4: Result := Rec.TransDate;
    5: Result := Rec.Net;
  else 
    Result := Null;
  end;
end;
  
for x := 0 to STranFieldCount-1 do 
  case VarType(STranField(STran, x)) of 
    varString: Memo1.Lines.Add(VarToStr(STranField(STran, x)));
    varInt: Memo1.Lines.Add(VarToStr(STranField(STran, x)));
    ...
  end;

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Author Comment

by:alanjbrown
ID: 22808758
Ciuly, I would like to try using a class instead of a record but I don't know anything about classes at the moment so I am not sure if it will create other problems for me.

Geert, I don't want to have to change my functions when ever the record structure is changed.
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Expert Comment

by:2266180
ID: 22808771
well, try to give us examples of how you are using the record. if you are using a file of type record, then class won't do since you cannot have file of type class. there are other such scnearios, but better to see whatever you are using it for ;)
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Author Comment

by:alanjbrown
ID: 22808794
I am using files of type record. The purpose of the program is to read the file and convert the output, the conversion being based on the field types in the record. So it looks as if I won't be able to use classes. I have potentially a lot of different structures to work with, that is why I need a generic process rather than to create different functions for each record structure.
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Expert Comment

by:2266180
ID: 22808857
the let's go the other way around: what kind of processing do you need to do which is so generic that a function like geert suggests is too much? what are you trying to accomplish?
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Author Comment

by:alanjbrown
ID: 22808894
Output as CSV the first record to have the field names from the record, then when each field is output it will converted into a formatted string depending upon the actual field type. For example a currency field would be output as '99,999.00' etc.
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Expert Comment

by:2266180
ID: 22808924
so you want to convert a binary file (with records) into a csv file?
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Author Comment

by:alanjbrown
ID: 22808948
yes but I want to add some proccessing / formatting to certain field types.
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Accepted Solution

by:
2266180 earned 250 total points
ID: 22811224
see this small demo I wrote: http://www.ciuly.com/delphi/rtti/binaryToCsv/index.html
read the explanations on the page on how to extend this to support most of the data types applicable.
if you have any questions about it, just ask.
0
 
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Author Comment

by:alanjbrown
ID: 22812157
Ciuly, thanks for the demo, it looks good although I won't be able to test it until this evening. I will get back to you later to award points etc.

I have an additional question regarding binary files which I will post as a new question.
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Expert Comment

by:2266180
ID: 22812227
ok
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