Re: is there a compiler warning for this piece of code ?

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

Victor,

Thanks for your thoughts - I think your speculation as to the history of the
code is probably correct.

I still have no easy way of parsing the codebase to see how prevalent this
is.
I'm fairly sure there are only a couple - it just would be more comforting
if I could get the
compiler to tell me about them automatically.
Maybe MS could add this to the "constant value"/"unreachable code" compiler
checks in some future VC7 fixpack.

regards
John

"Victor Bazarov" <v.Abazarov@xxxxxxxxxxxx> wrote in message
news:OyLcYO#XFHA.3540@xxxxxxxxxxxxxxxxxxxxxxx
> Kevin D. Quitt wrote:
> > On Mon, 23 May 2005 19:50:51 +0100, "John Kelly"
> > <john_kelly@xxxxxxxxxxxxxxxxx> wrote:
> >
> >>Maybe i've misunderstood, but i've interpreted "if (fred == NULL)" to
mean
> >>"if the address of the first element in the array fred (that is,
&fred[0])
> >>is NULL".
> >
> >
> > You've misunderstood. You are comparing the address of fred to NULL,
not
> > the first element of fred. An element of a char array cannot be NULL;
it
> > might be NUL, however.
>
> No, it's you who misunderstood. (fred == NULL) is comparing the address
> of the _first_element_ of 'fred' to NULL, i.e. (&fred[0] == NULL) or
> (fred + 0 == NULL), not the _contents_ of the first element. In C as in
> C++ the name of the array used in an expression _often_ decays to the
> _address_ of the first element.
>
> The address of 'fred' would be '&fred'. In case of an array the address
> of the array and the address of its first element have the same value but
> different types.
>
> My speculation (as was the OP's probably) that the code might look like
>
> char* fred = new char[100];
> if (fred == NULL)
> {
> // no more memory left, report and bail out
> }
>
> some time ago (now 'new' doesn't return NULL unless you ask it to). It
> probably was changed later to
>
> char fred[100];
>
> by a big sweep of replacing all 'new' with statically-sized arrays (which
> are faster without a doubt). The code that verified the allocation was
> left behind.
>
> >>Given this is a stack variable, this will never be true - so i'd count
this
> >>as unreachable code
> >
> >
> > Incorrect. The uninitialized value could be zero as easily as any other
> > value. Given that you are defining fred, it cannot be NULL, so is just
so
> > happens the code is unreachable.
>
> ??? I think your "Incorrect" is based on some assumptions you made which
> were incorrect themselves.
>
> > [...]
>
> V


.

Relevant Pages

  • Re: is there a compiler warning for this piece of code ?
    ... "if the address of the first element in the array fred ... were incorrect themselves. ...
    (microsoft.public.vc.language)
  • Re: Get the results in reverse order
    ... I need to get the first element, that is the newest, and then the rest ... How do i get the rest of the rows in reverse order? ... Store everything in an array. ... Prototype.js was written by people who don't know javascript for people ...
    (comp.lang.php)
  • Re: Fast lookup of ranges
    ... I have a peculiar (atleast to me) problem before my hand. ... big table with numeric ranges in each row. ... and the first element is always less than ... Chose an array length N, the larger the faster we can search. ...
    (comp.programming)
  • Re: writing get_script()
    ... to the highest index. ... remove the first element from an array. ... print "$verse $script\n"; ...
    (comp.lang.perl.misc)
  • Re: Please, I am going insane: First element access causing ArrayIndexOutOfBoundsException:0
    ... I have an array created that has ... I feed the results of the query into the array... ... same error when i try to access the first element. ... its own prepared statement and resultset and it fixed the problem. ...
    (comp.lang.java.programmer)