In Delphi/Free Pascal: is ^ an operator or does it simply denote a pointer type?

delphi pointers pascal dereference

11,181

When ^ is used as part of a type (typically in a type or variable declaration) it means "pointer to".

Example:

type
  PInteger = ^Integer;

When ^ is used as a unary postfix operator, it means "dereference that pointer". So in this case it means "Print what P points to" or "Print the target of P".

Example:

var
  i: integer; 
  a: integer;     
  Pi: PInteger;
begin
  i:= 100;
  Pi:= @i;  <<--- Fill pointer to i with the address of i
  a:= Pi^;  <<--- Complicated way of writing (a:= i)
            <<--- Read: Let A be what the pointer_to_i points to
  Pi^:= 200;<<--- Complicated way of writing (i:= 200)
  writeln('i = '+IntToStr(i)+' and a = '+IntToStr(a));

11,181

Adam Scott Roan

hi there. i'm a hobbyist programmer. my tools-of-the-trade are typically as follows: 1) C 2) Pascal and its decedents (Delphi, Free Pascal, Lazarus.) I use C when I'm in Linux, and Delphi otherwise... but now with Lazarus becoming more and more mature, my Pascal skills have been intersecting with the *NIX world. my itinerary for "apps i have written" is slightly defunct after a major hard drive failure about ~1.5 years ago, however, here's a rough list of what I have completed... both past and future/present. 1) zsnes patch. i wrote a patch that sends ROM files to the client computer if it did not have the file locally. technically this is usually illegal but there's a method to detect copyrighted signatures in a ROM file, but I never implemented it. I am going to work on this again soon with added portability. 2) a simple binary clock. C+SDL. very simple and straightforward. 3) tic-tac-toe game with complete procedural AI routines. C+SDL+OpenGL. 4) misc. other softs that no one cares about! that's about it. i'm usually in the C++ channel helping others, so if you have a specific question, feel free to ask it there.

Updated on June 05, 2022

Comments

Adam Scott Roan almost 2 years
In Delphi/Free Pascal: is ^ an operator or does it simply denote a pointer type?

Sample code
```
program Project1;

{$APPTYPE CONSOLE}

var
    P: ^Integer;

begin
    New(P);

    P^ := 20;
    writeln(P^); // How do I read this statement aloud? P is a pointer?

    Dispose(P);

    readln;
end
```
- Warren P about 12 years
  
  If you've used C or C++, you can translate ^ where you see it to basically the same thing as * except that ^ is postfix (written after) when used to dereference and before when used to declare a pointer to X, whereas C consistently you put the * before the thing it's dereferencing. X^ == (*X).
- OnTheFly about 12 years
  
  P^ reads [pointer] P dereferenced. Confer: ^T reads reference to type T. First is for the expressions, but latter is for the declarations.
- Jørn E. Angeltveit about 12 years
  
  BTW. The power operator in Delphi is not ^. You need to use function Power(x, y).
Adam Scott Roan about 12 years

thanks, I was thinking of prefix vs postfix... I'm just confused with the notation for some reason!
Dampsquid about 12 years

interestingly though if the pointer is a pointer to a record either R^.value or R.value is allowed (delphi 7 anyway)
CodesInChaos about 12 years

@Dampsquid Yes, the . operator implicitly dereferences the pointer to the left, if necessary. Unlike c where there is both . and the dereferencing equivalent ->. | And when you get to function pointers, the syntax gets really confusing since even the address-taking operator @ can become optional.
Adam Scott Roan about 12 years

thanks again!!!* like I said, I was confused because I couldn't find a single piece of documentation stating that it was even an operator! but now it makes sense. :>
Adam Scott Roan about 12 years

@Dampsquid that's quite weird... the notation must not carry levels of indirection, which is really weird.
OnTheFly about 12 years

IMO, you are adding unnecessary complexities with prefix and postfix. This concept does not burden Pascal as language. @AdamScottRoan, re: membership operator .: Delphi does automatic dereferencing for pointers to structured types.
CodesInChaos about 12 years

@user539484 pascal has both prefix(@,+,-) and postfix(^) operators. No idea what you mean.
OnTheFly about 12 years

@CodeInChaos, in Pascal, ^ is postfix-only.
OnTheFly about 12 years

@Johan, where did you see an operator there? Or expression? It is a declaration, duh!
Marco van de Voort over 7 years

CodeInChaos: the "." pointer derefence is specific to Delphi dialects. In normal Pascals (including Delphi predecessor Turbo Pascal) you need to dereference and select field: recordptrvar^.fieldname. In freepascal it depends on dialect mode.
Marco van de Voort over 7 years

Johan: as operator it is, type declaration (including casts) is a different story.