Messages in this thread | | | Date | Thu, 5 Apr 2001 09:13:02 -0400 | From | Ben Collins <> | Subject | Re: 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 ' `---=========------=======-------------=-=-----=-===-======-------=--=---' - 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/
| |