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Insert

procedure Insert(Index: Integer; S: string);

Example​

procedure AddHeading(const Items: TStringList);
begin
  if not Items.Sorted then
    Items.Insert(0, 'Heading');
end;

Usage​

Invokes the string list's abstract operation to insert a string before a zero-based position.

  • Index = Count is the append position; Index > Count and negative indexes are invalid.
  • Do not call on a sorted TStringList.
  • Saved numeric indexes after the insertion may now refer to different entries.

Additional Technical Info​

Insert is declared by hidden ancestor TStrings and is normally used through a concrete visible descendant such as TStringList. The base TStrings class has no storage implementation.

Source-backed behaviour​

TStrings.Insert is abstract. TStringList.Insert delegates to its pair insertion with a nil object, requires 0 <= Index <= Count, and raises EStringListError when Sorted=True; sorted lists must use Add so the comparison logic chooses the position.

A successful insertion shifts the previous entry at Index and all later entries upward. It can allocate capacity and emits change notifications.

InsertObject inserts a paired object. Add is appropriate when order is descendant-controlled. Delete shifts later indexes down.

Official RTL references​

Created 2026-07-15