| Nasser Abbasi 2006-05-26, 7:04 pm |
|
"Richard Maine" <nospam@see.signature> wrote in message
news:1hfxsjh.t88mchrssv9cN%nospam@see.signature...
> Ludovic Brenta <ludovic@ludovic-brenta.org> wrote:
>
> [that an loop index shall not change within a loop]
>
> Others have replied some, but let me make my attempt at clarification
> because yes, you seem to be  about multiple related things here.
>
> Yes, there is a Fortran language rule that a loop index shall not be
> changed while a loop is executing. Compilers are not required to enforce
> that rule, but essentially all compilers make at least some attempt to
> enforce it and catch the simple cases, which is most cases, but not all.
> There are cases where the violation of the rule is hard to detect,
> because the change occurs in some other procedure.
>
Hello;
<about loop counters being changed.>
I am not sure if there is supposed to compiler flag to enforce this or not,
you do not seem to imply that, so I did this very simple test, please see:
------------ test for checking on changing loop index----
$ cat a.f90
PROGRAM MAIN
DO I=1,10
CALL foo(I)
PRINT *,I
END DO
END PROGRAM
SUBROUTINE foo(I)
I=I+1
END SUBROUTINE
------------- end program ------
$ g95 a.f90
$ ./a.exe
2
4
6
8
10
12
14
16
18
20
--------- end run ---------
I did the same in Ada:
--------- Ada -------
procedure Main is
PROCEDURE foo(I: in out integer) IS
begin
I:=I+1;
end foo;
BEGIN
FOR I IN 1..10 LOOP
foo(I);
END LOOP;
END Main;
------- end ada ----
The above will not even be allowed to compile since Ada wants 'I' to be an
actual variable.
The compile error I get is "actual for I must be a variable"
This means I am not even allowed to use "I" in a call.
This eliminate the problem from accidentally change the loop counter.
Nasser
|