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    SubjectRe: [Infiniband-general] Getting an Infiniband access layer in theLinux kernel
    That's one of the many reasons of using do-while macros..
    Other than compilation error, it may generate wrong code too!
    this is a FAQ in kernel newbies , look at:
    http://www.kernelnewbies.org/faq/index.php3#dowhile

    thanks, som.

    Roland Dreier wrote:

    > Richard> If some major changes are being considered, I think it's
    > Richard> time to get rid of the:
    >
    > Richard> do { } while(0) stuff that permiates a lot of MACROS and
    > Richard> just use the { } as they were designed.
    >
    > Richard> Before everybody screams, think. It's perfectly correct
    > Richard> to start a new "program unit" without a conditional
    > Richard> expression. You just add a curley-brace, then close the
    > Richard> brace when you are though.
    >
    >This is totally, totally wrong. If you get rid of do { } while (0),
    >then you can't use the macro in an if statement. Read any C FAQ for
    >details, or try the following:
    >
    > #define MAC(x) { x = x + 1; }
    >
    > int main() {
    > int x = 0;
    >
    > if (1)
    > MAC(x);
    > else
    > x = x - 1;
    > }
    >
    >I get the following (correct) error:
    >
    > $ gcc a.c
    > a.c: In function `main':
    > a.c:8: syntax error before "else"
    > $ gcc --version
    > gcc (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-20)
    >
    >because
    >
    > if (1)
    > { x = x + 1 } ; /* <-- note semicolon
    > else
    > x = x - 1;
    >
    >is not correct C.
    >
    >By the way, it is possible to use parentheses and commas for some
    >simple macros, so for example the following is OK:
    >
    > #define MAC(x) ( x = x + 1, x = x * 2 )
    >
    > int main() {
    > int x = 0;
    >
    > if (1)
    > MAC(x);
    > else
    > x = x - 1;
    > }
    >
    >However I don't see anything wrong with the perfectly standard "do { }
    >while (0)" idiom. Certainly if some compiler generates worse code for
    >that construct that just a plain { }, _that_ is a compiler bug that we
    >shouldn't have to work around.
    >
    > - Roland
    >
    >
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    >
    >



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