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SubjectRe: asm/unistd.h
On Thu, Apr 05, 2001 at 09:58:43AM -0300, Sarda?ons, Eliel wrote:
> I'm taking a look at the linux code and I don't understand how do you
> programm...mmm (?) may be i'm a stupid why in include/asm/unistd.h in some
> macros you use this:
>
> do {
> ...
> } while (0)

Imagine a macro of several lines of code like:

#define FOO(x) \
printf("arg is %s\n", x); \
do_something_useful(x);

Now imagine using it like:

if (blah == 2)
FOO(blah);

This interprets to

if (blah == 2)
printf("arg is %s\n", blah);
do_something_useful(blah);;

As you can see, the "if" then only encompasses the printf, and the
do_something_useful() call is unconditional (not within the scope of the
if), like you wanted it.

So, by using a block like do{...}while(0), you would get this:

if (blah == 2)
do {
printf("arg is %s\n", blah);
do_something_useful(blah);
} while (0);

Which is exactly what you want.

--
-----------=======-=-======-=========-----------=====------------=-=------
/ Ben Collins -- ...on that fantastic voyage... -- Debian GNU/Linux \
` bcollins@debian.org -- bcollins@openldap.org -- bcollins@linux.com '
`---=========------=======-------------=-=-----=-===-======-------=--=---'
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