eg.
#define crazy(a, b) \
a = b; \
b = a;
if(\*something*\)
crazy(a,b)
Look at this carefully, which line do you think is associated with the if() here? Only a = b;, NOT b =a; !
but if the macro was written like this:
#define crazy(a, b) \
do { \
a = b; \
b = a; \
}
both the lines would be associated with the "true" case of if() above.
HTH,
Mayank
On Dec 26, 2007 11:44 PM, Maneesh Singhal <mnshsnghl@xxxxxxxxx > wrote:
crazy(a,b)
Look at this carefully, which line do you think is associated with the if() here? Only a = b;, NOT b =a; !
but if the macro was written like this:
#define crazy(a, b) \
do { \
a = b; \
b = a; \
}
both the lines would be associated with the "true" case of if() above.
HTH,
Mayank
On Dec 26, 2007 11:44 PM, Maneesh Singhal <mnshsnghl@xxxxxxxxx > wrote:
One more reason could be, by using do-while(0) thingy, one could use
'break' statement at any place just to come out of the macro at once.
Thanks.
Anupam Kapoor wrote:
> sahlot arvind <asahlot@gmail> wrote:
> ,----
> | > Recently I started looking into linux kernel and trying to understand
> | > the code. I am working with linux-2.6.9. in file
> | > include/llinux/list.h - I found something like this.
> | >
> | > #define INIT_LIST_HEAD(ptr) do { \
> | > (ptr)->next = (ptr); (ptr)->prev = (ptr); \
> | > } while (0)
> | >
> | >
> | > My question is why do we use a loop when we actually know that it is
> | > not going to execute more than once? Cannot we simply do -
> `----
> see: http://kernelnewbies.org/FAQ/DoWhile0
>
> anupam
>
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-Mayank
