Difference between revisions of "@"
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It should print <code>0</code> (zero), but prints <code>-256</code>. | It should print <code>0</code> (zero), but prints <code>-256</code>. | ||
With <code>{$typedaddress on}</code> compilation fails with an incompatible type error. | With <code>{$typedaddress on}</code> compilation fails with an incompatible type error. | ||
| + | You usually want the latter behavior (compile-time failure) instead of wasting time with hours of debugging. | ||
== read more == | == read more == | ||
Revision as of 02:55, 31 January 2018
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The address operator @ returns the address of a variable, procedure or function.
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 {$typedaddress on}.
Here some example to demonstrate, what produces with untyped pointers valid and functional code, but semantically outputs an erroneous result:
program typedAddress(input, output, stderr);
procedure incrementIntByRef(const ref: PByte);
begin
inc(ref^);
end;
var
foo: integer;
begin
foo := -1;
incrementIntByRef(@foo);
writeLn(foo);
end.It should print 0 (zero), but prints -256.
With {$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.
