CODEWITHSUNDEEP
delphitext-files
Jordon Draggon
Jordon Draggon

Reputation: 50

Delphi Looping through TextFile for specific string the copying that string to a variable

So line containing 'NVMEM' successfully deletes from the textfile. I actually want the opposite to happen where it will delete every line apart from the line containing the string 'NVMEM'. I tried changing the if statement under button 2's for loop, to an if not statement thinking that would work but it just deletes everything. Is there a way for me to be able to delete all of the lines apart from the one containing the stringy string.

implementation

{$R *.dfm}

procedure TForm3.Button1Click(Sender: TObject);
var
NVE: TextFile;

begin
if not FileExists('NVE.txt') then
  begin
  AssignFile(NVE, 'NVE.txt');
  Rewrite(NVE);

  WriteLn(NVE, 'abcdefg') ;
  WriteLn(NVE, 'hijklmnop')      ;
  WriteLn(NVE, 'fmdiomfsa');
  WriteLn(NVE, 'heres the line with NVMEM'); //line I want to parse


  ShowMessage('You have successfully created the file amigo');
  CloseFile(NVE);

  end;


if FileExists('NVE.txt') then
  begin
    AssignFile(NVE,'NVE.txt');
    Rewrite(NVE);

    WriteLn(NVE, 'abcdefg') ;
    WriteLn(NVE, 'hijklmnop');
    WriteLn(NVE, 'hope i got that right');
    WriteLn(NVE, 'heres the line with NVMEM'); //line I want to parse

      ShowMessage('Eso Final');
      CloseFile(NVE);

  end;
end;

procedure TForm3.Button2Click(Sender: TObject);
var
NVE: string;
i : integer;
raw_data1,stringy: string;
raw_data: TstringList;
begin
  stringy := 'NVMEM';
  i := 0;
  raw_data := TStringlist.Create;
  try
    raw_data.LoadFromFile('NVE.txt');
    for i := raw_data.Count-1 downto 0 do
      if pos(stringy, raw_data[i])<>0 then
        raw_data.Delete(i);
    raw_data.SaveToFile('NVE.txt');
  finally
    raw_data.free;
  end;
end;



end.

Upvotes: 1

Views: 736

Answers (1)

Tom Brunberg
Tom Brunberg

Reputation: 21045

First recall what function Pos(SubStr, Str: string): integer does.

`Pos()` returns the position of `SubStr` within `Str` if `SubStr` is included in `Str`.
`Pos()` returns 0 when `SubStr` is not included in `Str`.

Now, to these lines of code in Button2Click() (where i is the index of a line in raw_data) that you want to modify to delete all lines except the one that contains "NVMEM":

  if pos(stringy, raw_data[i]) <> 0 then  // your current code
    raw_data.Delete(i);

Which can be spelled out as "if stringy is included in raw_data[i], then delete raw_data[i]" and which is opposite of what you want.

To turn the logic around, that is, "if stringy is not included in raw_data[i], then delete raw_data[i]", do as follows:

Pos() returns 0 when SubStr is not included in Str, ergo, the condition for deleting a row should be:

  if pos(stringy, raw_data[i]) = 0 then   // change `<>` to `=`
    raw_data.Delete(i);

That will leave you with one line left in the raw_data: TStringList, the line that contains "NVMEM"

Upvotes: 1

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