[fpc-devel] open array and address of "@" / crash, why?

[Michael Van Canneyt]

On Sun, 30 Mar 2014, Martin Frb wrote:

> On 30/03/2014 14:35, Jonas Maebe wrote:
>> On 30/03/14 15:24, Martin Frb wrote:
>>> The below program compiles fine (and generates no warning (fpc 2.6.2 /
>>> win 32)
>> 
>> It only compiles fine with the (default) {$t-}. If you add {$t+}, it 
>> doesn't compile. Without typed pointers, the result of the @-operator is an 
>> untyped pointer, which by definition is assignment-compatible with all 
>> other pointer types.
>> 
>> Making {$t+} the default is hard because it could break existing, correct 
>> code (e.g., "untypedptr:=@wordvar+1" would result in a pointer 2 bytes 
>> after @wordvar instead of 1 with {$t+}).
>
> Ah yes, so easy to forget... (Now I remember)
>
>
> Slight change, and  I get
> Fatal: Compilation aborted
>
>
> program project1;
> {$t+}
> type
>  TA = array of integer;
>  PA = ^TA;
> var
>  a : array of integer;
>  a1: PA;
>
> procedure Foo(var c: array of integer; var c1: PA);
> begin
>  //c1:= @c;
>
>  writeln( (@c)^[1] );
>
>  //writeln(PInteger(c1)^);
>  //writeln(c1^[1]);
>  readln;
> end;
>
> begin
>  SetLength(a,5);
>  a[0]:= 100;
>  a[1]:= 101;
>  a1:=@a;

If you are counting on the implicit pointer=array as in C, 
then this should probably be a1:=@A[0] or a1:=PA(a)

Michael.