TStack.Push Method

Push stack item.

Pascal

procedure Push(const Value: T);

C++

__fastcall Push(const T Value);

Description

This method inserts one item onto the top of the stack. Count is incremented by 1. You can push nil onto the stack. The stack's capacity is automatically increased if necessary.

An OnNotify event occurs indicating an item was added to the stack.

This is a O(1) operation unless the capacity must increase. In this case, it is O(n), where n is Count.

Delphi Examples:

Copy Code

{
This example demonstrates the usage of the generic TStack class.
}
procedure TForm3.Button1Click(Sender: TObject);
var
  Stack: TStack<String>;
begin
  { Create a new stack }
  Stack := TStack<String>.Create();

  { Register a notification call-back }
  Stack.OnNotify := StackChanged;

  { Push some items up the stack }
  Stack.Push('John');
  Stack.Push('Mary');
  Stack.Push('Bob');
  Stack.Push('Anna');
  Stack.Push('Erica');

  { Show the last pushed element without modifying the stack }
  MessageDlg('Last pushed element is: "' + Stack.Peek() + '".', mtInformation, [mbOK], 0);

  { Extract the top element: "John" }
  Stack.Extract();

  { Reduce the capacity }
  Stack.TrimExcess();

  { The remaining count of elements }
  MessageDlg('The stack contains ' + IntToStr(Stack.Count) + ' elements.', mtInformation, [mbOK], 0);

  { Show the last pushed element by modifying the stack }
  MessageDlg('Last pushed element is: "' + Stack.Pop() + '".', mtInformation, [mbOK], 0);

  { Clear the stack }
  Stack.Clear();

  { Destroy the stack completely }
  Stack.Free;
end;

procedure TForm3.StackChanged(Sender: TObject; const Item: String; Action: TCollectionNotification);
begin
  { This method is called by the Stack everytime a change occurs }
  if Action = cnAdded then
     MessageDlg('Element added: ' + Item, mtInformation, [mbOK], 0)
  else if Action = cnRemoved then
     MessageDlg('Element removed: ' + Item, mtInformation, [mbOK], 0)
  else if Action = cnExtracted then
     MessageDlg('Element extracted: ' + Item, mtInformation, [mbOK], 0)
end;