On Wed, 2009-09-02 at 15:17 +0530, Anuz Pratap Singh Tomar wrote:
> On Wed, Sep 2, 2009 at 2:30 PM, Bernd Petrovitsch <bernd@xxxxxxxxx>
> wrote:
> On Wed, 2009-09-02 at 13:31 +0530, Anuz Pratap Singh Tomar
> wrote:
> > that part of code wont be executed.
[...]
> Then why not simply use "do { } while (0)" or similar?
>
> [
> > On Wed, Sep 2, 2009 at 1:24 PM, luca ellero
> <lroluk@xxxxxxxxx> wrote:
> [...]
> > can someone please explain me the meaning/benefits
> of the "if
> > (0)" statement?
> #if 0 is equivalent to blank, this is done while preprocessing, this
> type of macro is used commonly to define some sort of debug(print
> statement)
> and if i am not wrong do{}while(0) will execute atleast once.
Yes, of course. Sorry, I meant an empty "do{}while(0)" (or similar
expression) which evaluates as a syntactic correct C expression.
BTW the "if(0)" above (and "#if 0" and an empty "do{}while(0)") have
also the issue that side effects (function calls, ++, --, += -=, ...) in
the parameters of the printk() get lost (which may be good[0] or bad).
That shouldn't be a problem in the Linux kernel as that is generally
avoided but in general that maybe a problem.
Bernd
[0]: It may be even good if the side effects are just there for the
printk() as such (e.g. formatting some data into a string just for
the printk/syslog/printf) but irrelevant for the "normal" program
flow.
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