@

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@

The address operator @ returns the address of an identifier that is associated with an address (usually a variable or routine, but also a label).

Normally, the value @ returns is an untyped pointer. If you are handling pointers a lot, and want to mitigate issues with passing references of wrong type's target, you have use the directive {$typedaddress on}.

Here some example to demonstrate, what produces with untyped pointers valid and functional code, but semantically outputs an erroneous result:

  1. program untypedAddressDemo(input, output, stderr);
  2.  
  3. procedure incrementIntByRef(const ref: PByte);
  4. begin
  5. 	inc(ref^);
  6. end;
  7.  
  8. var
  9. 	foo: integer;
  10. begin
  11. 	foo := -1;
  12. 	incrementIntByRef(@foo);
  13. 	writeLn(foo);
  14. end.

It was intended, that 0 (zero) gets printed, but the program prints -256 instead. With {$typedaddress on} compilation fails with an incompatible type error. You usually want the latter behavior (compile-time failure) instead of wasting time with hours of debugging.

other remarks

  • In ASCII the character @ (AT sign): has the value 64.

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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)