^

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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.

 1program pointerDemo(input, output, stderr);
 2
 3type
 4	listItem = record
 5		payload: integer;
 6		// next _points_ _to_ a list item
 7		next: ^listItem;
 8	end;
 9
10var
11	start: ^listItem;
12
13begin
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);
25end.

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

• {$pointerMath off} disallows usage of pointers in arithmetic expressions
• {$typedAddress on} in conjunction with the @-address-operator
• {$modeSwitch autoDeref-}