Significance of do ... while (0)

Significance of do ... while (0)

[krishna]

Hi all,

    Can any one explain the importance of do  ... while (0)

Regards,
Krishna Chaitanya

#define STATS_SET_HIGH(x)       do { if ((x)->num_active > (x)->high_mark) \
                                        (x)->high_mark = (x)->num_active; \
                                } while (0)
#define STATS_INC_ERR(x)        ((x)->errors++)
#define STATS_SET_FREEABLE(x, i) \
                                do { if ((x)->max_freeable < i) \
                                        (x)->max_freeable = i; \
                                } while (0)
                                                                                                                              
 
#define STATS_INC_ALLOCHIT(x)   atomic_inc(&(x)->allochit)
#define STATS_INC_ALLOCMISS(x)  atomic_inc(&(x)->allocmiss)
#define STATS_INC_FREEHIT(x)    atomic_inc(&(x)->freehit)
#define STATS_INC_FREEMISS(x)   atomic_inc(&(x)->freemiss)
#else
#define STATS_INC_ACTIVE(x)     do { } while (0)
#define STATS_DEC_ACTIVE(x)     do { } while (0)
#define STATS_INC_ALLOCED(x)    do { } while (0)
#define STATS_INC_GROWN(x)      do { } while (0)
#define STATS_INC_REAPED(x)     do { } while (0)
#define STATS_SET_HIGH(x)       do { } while (0)
#define STATS_INC_ERR(x)        do { } while (0)
#define STATS_SET_FREEABLE(x, i) \
                                do { } while (0)
                                                                                                                              
 
#define STATS_INC_ALLOCHIT(x)   do { } while (0)
#define STATS_INC_ALLOCMISS(x)  do { } while (0)
#define STATS_INC_FREEHIT(x)    do { } while (0)
#define STATS_INC_FREEMISS(x)   do { } while (0)

Re: Significance of do ... while (0)

[Dave Jones]

On Fri, Dec 17, 2004 at 09:39:00AM +0530, krishna wrote:
 > Hi all,
 > 
 >    Can any one explain the importance of do  ... while (0)

http://www.kernelnewbies.org/faq/


		Dave

Re: Significance of do ... while (0)

[Mitchell Blank Jr]

krishna wrote:
>    Can any one explain the importance of do  ... while (0)

It's a standard C programming practice; more info is available from
your local search engine:
  http://www.google.com/search?lr=&c2coff=1&q=%22while%280%29%22

-Mitch

Re: Significance of do ... while (0)

[krishna]

Thank you very much

Dave Jones wrote:

>On Fri, Dec 17, 2004 at 09:39:00AM +0530, krishna wrote:
> > Hi all,
> > 
> >    Can any one explain the importance of do  ... while (0)
>
>http://www.kernelnewbies.org/faq/
>
>
>		Dave
>
>
>  
>

Re: Significance of do ... while (0)

[Jan Engelhardt]

>>    Can any one explain the importance of do  ... while (0)
>
>It's a standard C programming practice; more info is available from
>your local search engine:
>  http://www.google.com/search?lr=&c2coff=1&q=%22while%280%29%22

Why? {} would suffice, no need to do{}while(0)



Jan Engelhardt
-- 
ENOSPC

Re: Significance of do ... while (0)

[vlobanov]

> >>    Can any one explain the importance of do  ... while (0)
> >
> >It's a standard C programming practice; more info is available from
> >your local search engine:
> >  http://www.google.com/search?lr=&c2coff=1&q=%22while%280%29%22
>
> Why? {} would suffice, no need to do{}while(0)
>
>
>
> Jan Engelhardt
> --
> ENOSPC
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>

Unless I'm mistaken, it won't work in all cases. Example:

    #define foo(...) { ... /* nefarious macro stuff here */ ... }

    if (some_condition)
        foo();
    else
        // do something nifty

The above would expand to:

    if (some_condition) {
        /* nefarious macro stuff here */
    };
    else
        // do something nifty

And that's not quite right.

-Vadim Lobanov

Re: Significance of do ... while (0)

[Jan Engelhardt]

>> >>    Can any one explain the importance of do  ... while (0)
>> >It's a standard C programming practice; more info is available from
>> Why? {} would suffice, no need to do{}while(0)
>
>Unless I'm mistaken, it won't work in all cases. Example:
>    #define foo(...) { ... /* nefarious macro stuff here */ ... }
>    if (some_condition)
>        foo();
>    else
>        // do something nifty
>
>The above would expand to:
>
>    if (some_condition) {
>        /* nefarious macro stuff here */
>    };
>    else
>        // do something nifty
>
>And that's not quite right.

So it's best to always make some braces around ifs :)
Would be consistent with longer-than-one-statement blocks too.

if(some_cond) {
	MY_MACRO
}



Jan Engelhardt
-- 
ENOSPC