Lesson 13 · 13 of 20

TStringList in depth · Pascal

Sort, search and store name=value pairs with TStringList, the string list from the Classes unit that every Free Pascal and Lazarus program uses.

Pascal · TStringList in depth in DMarlon Studio: the example's code and its output in the terminal

`TStringList` (in the Classes unit) is Pascal's Swiss army knife for text. With `Sorted := True`, the list sorts itself and every later Add goes straight to its place. `CommaText` works both ways: assigning it splits the text at the commas; reading it joins the items.

`Find` runs a binary search, very fast on large lists, and only works when the list is sorted. It returns True if it finds the text and puts its position in the index parameter: Navarro is at 3, counting from 0. For unsorted lists there is IndexOf. When Castro is added, it lands between Blanco and Garcia with no re-sorting needed.

The second list holds `name=value` lines, like a configuration file (here, the connection to an Odoo database). `Values['port']` returns the value for that name, and assigning it changes the line if it exists or appends a new one, as happens with user.

`Names[3]` and `ValueFromIndex[3]` give the name and value of line 3 by position. With LoadFromFile and SaveToFile the same list reads and writes a whole .ini or .conf file in one line. It is an object, so it is freed in the finally block.

Code · main.pas

program main;uses Classes;var  clients, config: TStringList;  index: Integer;begin  clients := TStringList.Create;  config := TStringList.Create;  try    clients.Sorted := True;  // sorts and keeps every Add in its place    clients.CommaText := 'Ruiz,Alonso,Navarro,Garcia,Blanco';    WriteLn('Clients: ', clients.CommaText);    if clients.Find('Navarro', index) then  // binary search      WriteLn('Navarro is at index ', index);    clients.Add('Castro');    WriteLn('With Castro: ', clients.CommaText);    config.Add('host=localhost');    config.Add('port=8069');    config.Add('database=odoo_demo');    WriteLn('Port: ', config.Values['port']);    config.Values['port'] := '8070';   // changes an existing name    config.Values['user'] := 'admin';  // a new name is appended    WriteLn(config.Names[3], ' = ', config.ValueFromIndex[3]);    WriteLn('Config: ', config.CommaText);  finally    clients.Free;    config.Free;  end;end.

Output · fpc main.pas && ./main

Clients: Alonso,Blanco,Garcia,Navarro,Ruiz
Navarro is at index 3
With Castro: Alonso,Blanco,Castro,Garcia,Navarro,Ruiz
Port: 8069
user = admin
Config: host=localhost,port=8070,database=odoo_demo,user=admin

Key points

Sorted := True sorts and keeps order on every Add.
CommaText splits and joins comma-separated text.
Find searches fast, but only in sorted lists.
Values['name'] reads and writes name=value pairs.
LoadFromFile and SaveToFile load and save the whole list.

Exercise

Save config to odoo.conf with SaveToFile, create another TStringList, load the file with LoadFromFile and print its Values['database'].