Question

Let me explain by an example. In Delphi, you can write

procedure TForm1.FormKeyPress(Sender: TObject; var Key: Char);
begin
  if Key = ^C then
    ShowMessage('The user wants to copy something.')
  else if Key = ^V then
    ShowMessage('The user wants to paste.')
end;

to check for Ctrl+C and Ctrl+V keyboard commands. In fact, the same syntax works for Ctrl+A, where A is any character, and — of course — you can also use a case statement instead of ifs. You can even do ShowMessage(^A), so, apparently, ^A is considered a char.

However, when browsing the official Delphi documentation, I cannot find any reference to this syntax. But maybe the ^A syntax is so common that it is understood as a part of the underlying plain text file format? Or is it simply an undocumented feature of the Delphi programming language? (Notice that the above constructions are actually used in the RTL/VCL source code. But, of course, Embarcadero, and Embarcadero alone, is allowed to use undocumented features, if any such exists.)

Answer 1

This is from long ago as an escape character to enable you to have consts for control characters in a more readable way.

const
  CtrlC = ^C;
begin
  Write(Ord(CtrlC));
end.

This defines a Char constant with value #3, then writes 3 in Borland Pascal 7, and I remember seeing it years before that too.

I just checked the Turbo Pascal 5.0 and Borland Pascal 7.0 languages guides, but could not find it, so it seems undocumented.

Edit:
I do remember this was a Borland thing, and just checked: it is not part of the ISO Pascal standard (formerly this was ANSI Pascal Standard, thanks Sertac for noticing this).

It is documented in the Free Pascal documentation.

SGI uses the backslash as escape character, as per their docs.

More Edit: I found it documented in Delphi in a Nutshell and the Delphi Basics site.

Found it: Just found it on page 37 of the Turbo Pascal 3 Reference Manual.

–jeroen