Can anyone explain the purpose of this #define...
#define __cpu_raise_softirq(cpu, nr) do { softirq_pending(cpu) |= 1UL <<
(nr); } while (0) // from interrupt.h
...versus the more "plain"...
#define __cpu_raise_softirq(cpu,nr) softirq_pending(cpu |= 1UL << (nr).
In otherwords, what's the use of a do{X}while(0) "loop" instead of just
X. I'm not the world's best trained C programmer, so forgive me if I
sound stupid.
Josh
On Sun, Dec 22, 2002 at 12:36:32AM -0500, Joshua Stewart wrote:
>
> In otherwords, what's the use of a do{X}while(0) "loop" instead of just
> X. I'm not the world's best trained C programmer, so forgive me if I
> sound stupid.
http://www.kernelnewbies.org/faq/index.php3#dowhile
Hope that helps,
greg k-h
Hi Joshua :)
> In otherwords, what's the use of a do{X}while(0) "loop" instead of
> just X. I'm not the world's best trained C programmer, so forgive
> me if I sound stupid.
First, you do not sound stupid at all.
Second. The do...while use in macros is to avoid the 'swallow
semicolon' effect ;)) In other words, it makes the entire macro
appear as a single statement. This avoids problems with 'else'
constructs with macros that expand to multiple statements.
Someplace in the GNU cpp documentation you can find a far better
explanation of this effect and why the do...while helps (it makes the
macro a single statement...).
Hope that helps :)
Ra?l
Thanks for the help. It all makes perfect sense after thinking about it
from a preprecessor point of view. I'm just not used to using so many
macros and so I don't realize all the implications of preprocessing
quite yet. But, I'm learning.
Josh
On Sun, 2002-12-22 at 00:35, Greg KH wrote:
> On Sun, Dec 22, 2002 at 12:36:32AM -0500, Joshua Stewart wrote:
> >
> > In otherwords, what's the use of a do{X}while(0) "loop" instead of just
> > X. I'm not the world's best trained C programmer, so forgive me if I
> > sound stupid.
>
> http://www.kernelnewbies.org/faq/index.php3#dowhile
>
> Hope that helps,
>
> greg k-h
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