@

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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:

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

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.

read more

• The @ operator
• Typed address operator (@)
• system.addr