On 5/30/2014 2:43 AM, Peter Dufault wrote:
> On May 29, 2014, at 17:47 , Gedare Bloom <ged...@rtems.org> wrote:
>
>> You understood precisely. I think it was not permitted in C90 perhaps?
>> We should revisit it, but I think historically all variables are
>> declared at the top of the function.
> I'll dig up K&R, but I'm 95% sure it's been supported from the beginning.
> What hasn't always been supported is declaring variables anywhere other than
> after an opening bracket:
>
> /* Local block */
> {
> invoke_foo();
> int i;
> invoke_bar(&i);
> /* ... */
> }
>
> The argument for permitting declaration inside brackets (not as above, but as
> allowed by K&R) is to declare variables in as restrictive a scope as
> possible. The argument against is shadowing variables and getting subtle
> errors.
I don't know if we have it on but gcc has a shadowing warning which
is pretty effective. I did a code review for a project and learned they
had disabled warnings "because there were too many." When I turned
them back on, there were 1000s and among them:
+ parameters shadowing global variables.
+ outer scope local variables shadowing global variables.
+ inner scope local variables (from macros) shadowing local variables
GCC spotted all of the above. I am pretty confident in GCC's shadowing
detection. If we want to allow/encourage this, we need to turn
the warning on.
Also we need to remember to write down that macro parameters
start with an _ so as to avoid name collision. The project I reviewed
didn't follow that rule. They also didn't have naming rules which
prevented collisions between local, global, and parameters.
> Peter
> -----------------
> Peter Dufault
> HD Associates, Inc. Software and System Engineering
>
--
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joel.sherr...@oarcorp.com On-Line Applications Research
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