^

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^

In ASCII the character code decimal 94 (or hexadecimal 5E) is defined to be ^ (circumflex accent).

For any data type, a pointer type for that data can be declared using the operator ^ in front of the data type.


 1 program pointerDemo(input, output, stderr);
 2 
 3 type
 4 	listItem = record
 5 		payload: integer;
 6 		// next _points_ _to_ a list item
 7 		next: ^listItem;
 8 	end;
 9 
10 var
11 	start: ^listItem;
12 
13 begin
14 	new(start);
15 	if not assigned(start) then
16 	begin
17 		writeLn(stderr, 'obtaining memory for start failed');
18 		halt(1);
19 	end;

A pointer can be followed, dereferenced by appending a ^ to the identifier. Instead of having the memory address in your hands, you will look at the memory content at that address. If it is a typed pointer, operations and syntax for that type are valid, e.g. assignment in the following example.

21 	// _de-reference_ the pointer, i.e. follow it
22 	start^.payload := 7;
23 	
24 	dispose(start);
25 end.

However, attempting to follow a nil pointer will cause a runtime error (RTE 216 “general protection fault”). That is the situation the condition not assigned(start) in line 15 is supposed to catch.

see also


navigation bar: topic: Pascal symbols
single characters

+ (plus)  •  - (minus)  •  * (asterisk)  •  / (slash)
= (equal)  •  > (greater than)  •  < (less than)
. (period)  •  : (colon)  •  ; (semi colon)
^ (hat)  •  @ (at)  •  $ (dollar sign)  •  & (ampersand)

character pairs

<> (not equal)  •  := (becomes)  •  >< (symmetric difference)  •  // (double slash)