TStringList-TStrings Tutorial

TStringList

The TStringList (or TStrings) is much like a fancy dynamic array or Set of Strings (a set of strings is not possible in FPC). It will come in handy a lot when programming and I'm going to teach you basic TStringList usage!

<Delphi> program StrList; {$mode objfpc} uses

Classes, SysUtils;

var

 Str: TStringList;

begin

 Str := TStringList.Create; // This is needed when using this class(or most classes)
 Str.Add('Some String!');
 writeln('The stringlist now has ' + IntToStr(Str.Count) + ' string(s).');
 Readln;

end. </Delphi>

This is a simple console program that will create and add one string to a stringlist. Now here's some things you should know:

Create - Will create the string list for modifying.

Count - Is a counter for the number of strings in the List.

Add - Will allow you to add one string to the stringlist. It is a function that will return the Index of the String. This is where the counter comes in handy.

Delete - Will delete a string from the stringlist. Just know that you do not simply input the string, you have to input the index of the string. Like I said: it's like a fancy Dynamic Array.

IndexOf - Will return the index of the string in the list. If it is not found it returns -1.

Clear - Will clear the list.

Example

How about a more juicy example, Eh?

<Delphi> program StrList2; {$mode ObjFPC} uses Classes, SysUtils;

var

 Str: TStringList;
 S: String;
 Counter: Integer;

begin

 Str := TStringList.Create;
 Writeln('String List Test');
 repeat
   Writeln('Enter a string to add');
   Readln(S); 
   if (S = 'EXIT') then Halt;
   if not (S = ) then
   begin
     Counter := Str.Add(S);
     Writeln('String: ' + S + ' was Added!');
     Writeln('Index is: ' + IntToStr(Counter)); // The counter will always become the index of the last thing added
   end 
   else 
   begin
     Writeln('No data entered...');
   end;
 until (S = 'EXIT');

end. </Delphi>

File Handling

When using the TStringList you have 2 file handling procedures: SaveToFile and LoadFromFile. SavetoFile will save all strings in the list to a file. LoadFromFile will open the file and add the file data to the list string by string.

<Delphi> program StrListFile; {$mode objfpc} uses

Classes, SysUtils;

var

 Str: TStringList;

begin

 Str := TStringList.Create;
 Str.LoadFromFile('SomeFile.txt');
 Str.Add('Hello');
 Str.SaveToFile('SomeFile.txt');

end. </Delphi>

You just opened a file, edited it and saved it right back to were it was!

Dynamic string array comparison

TStringList is simply advanced object version of dynamic string array. Some methods have analogy:

Operation	array of string	TStringList
Variable declaration	StringList: array of string;	StringList: TStringList;
Initialization	implicit constructor	StringList := TStringList.Create
Set size	SetLength(StringList, X);	StringList.Size := X;
Get size	X := Length(StringList);	X := StringList.Size;
Add item	SetLength(StringList, Length(StringList) + 1); StringList[Length(StringList) - 1] := X;	StringList.Add(X);
Delete item	for I := Index to Length(StringList) - 2 do StringList[I] := StringList[I + 1]; SetLength(StringList, Length(StringList) - 1);	StringList.Delete(Index);
Remove all items	SetLength(StringList, 0);	StringList.Clear;
Finalization	implicit destructor	StringList.Free;

But TStringList offer much more functionality than basic structure as dynamic array.

Keep Learning

You can learn all the different procedures, functions and property's see TStringList documentation

IF you feel i might have left something out, Modify At Will!

Hope I helped!