^

^

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.

program pointerDemo(input, output, stderr);

type
    listItem = record
        payload: integer;
        // next _points_ _to_ a list item
        next: ^listItem;
    end;

var
    start: ^listItem;

begin
    new(start);
    if not assigned(start) then
    begin
        writeLn(stderr, 'obtaining memory for start failed');
        halt(1);
    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.

    // _de-reference_ the pointer, i.e. follow it
    start^.payload := 7;
    
    dispose(start);
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

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

From the Free Pascal wiki, page "^", as it stood on 2023-02-18 after a change by Kai Burghardt, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.