Why can the circumflex sign be used for control chars in Delphi and is it a good idea?

Question

I just came across an answer on SO with a curious syntax:

How do I include a newline character in a string in Delphi?

MyString := 'Hello,' + ^M + ^J + 'world!';

I've been using Delphi for several years now, but I didn't know you could use the circumflex sign for control characters.

Is this just a left over from the early Delphi or Turbo Pascal days?

Should it be used nowadays?

PS: I'm not asking about advice on the line break characters, there is sLineBreak and other methods as discussed in the original question.

I just noticed that it's a duplicate: http://stackoverflow.com/questions/4915941/delphi-a-syntax-documented-implied-or-undocumented — Jens Mühlenhoff, Oct 25 '12 at 06:35
Isn't that syntax easily confused with pointers? Or are ^M and ^J pointers? — Pieter B, Oct 25 '12 at 06:40
@PieterB And that's why having single character variable names is not a good idea. ;-) — GolezTrol, Oct 25 '12 at 06:43
@PieterB No, this is not pointer syntax. You can use PType = ^Type in a type declaration and dereference pointers in code using MyPointer^. — Jens Mühlenhoff, Oct 25 '12 at 06:43
@PieterB But you can't use a type in a const section. You also can't use a constant in a type section. It may look ambiguous, but on closer inspection it isn't. — Jens Mühlenhoff, Oct 25 '12 at 06:49
Well of course you can use a type in a const section if you use the `Constant: TSomeType = ` syntax :). — Jens Mühlenhoff, Oct 25 '12 at 06:50
@golez single character names for local loop variables is just fine. I'd always use i, j and k as my loop variable names for a matrix mul. — David Heffernan, Oct 25 '12 at 06:58

Arioch 'The · Answer 1 · 2019-06-26T13:47:01.193

No, it is not from Turbo Pascal days. It is from decades before TP, and before MS-DOS, and probably even before UNIX. Something old like first 300 bit-per-second dialup modems and DEC VT-52 terminal, RT-8 OS on PDP-8 machine and early version of C. Or maybe even older - though everything older to me is mere legends :-).

"^" sign is shortcut for "Ctrl" key. So ^C in traditional notation stands for Ctrl+C in Microsoft notation. That notation was vastly used for textmode menus in MS-DOS times, like in the aforementioned Turbo Pascal, Norton Utilities, DOS Navigator, etc.

Out of my memory you can consider "^" for "subtract 64".
So as Chr(65) is 'A' then Chr(1) would be ^A.
And ^@ would be #0 :-) AFAIR in MS-DOS times pressing Ctrl+Shift+"2/@" would actually produce #0 into BIOS keyboard buffer :-)

^[ would AFAIR be #27 aka Esc(ape) char - and if you run telnet.exe you would see it prompted as the escape character.

So Turbo Pascal long ago chosen to follow the time-blessed convention, and then rules of backward compatibility engaged ever since. Personally, i take 'bla-bla'^M^J'foo-baz' literal more string-like than 'bla-bla'#13#10'foo-baz' when you want it on one line. And constructing the value with plus is better fit when your literal takes several source lines.

The pity is that syntax highlighting in Delphi IDE is hopelessly broken on that kind of constants.

score 4 · Accepted Answer · answered Oct 25 '12 at 06:40

4

Yes this is a legacy from days of yore.

And no you should not get into the habit of using this feature. Remember that code is read more often than it is written. Always think of your readers who most likely won't know what that syntax means.

answered Oct 25 '12 at 06:40

David Heffernan

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The good ol' days of yore I presume? (I wasn't old enough to code back then, but it sounds like the past of Delphi development was awesome'r that it is now) – Jeff Oct 25 '12 at 06:52
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@Jeff, you're right about that, but this construct is from the days before Delphi was Delphi. :) – GolezTrol Oct 25 '12 at 07:01
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and before Pascal was Turboed! – Gerry Coll Oct 25 '12 at 07:29

score 0 · Answer 3 · answered Oct 25 '12 at 06:37

0

Yes, this is left over from TP days. You could also write your statement like this

mystring:= 'Hello'#13#10'world!';

which is probably less obscure and more easily understandable than using ^M and ^J. Of course, you should really define constants

const
 crlf = #13#10

begin
 mystring:= 'Hello' + crlf + 'world!';
end;

answered Oct 25 '12 at 06:37

No'am Newman

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You have `sLineBreak` if we are talking about defining constants ;-) – TLama Oct 25 '12 at 06:39
Also using "sLineBreak" will make the code "Cross Platform Aware" as it has different meaning on Windows and Mac :) – iPath ツ Oct 25 '12 at 18:33

Why can the circumflex sign be used for control chars in Delphi and is it a good idea?

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