On Tue, Aug 01, 2006 at 11:45:53AM +0159, Jiri Slaby wrote:
> Peter Zijlstra wrote:
> >On Tue, 2006-08-01 at 02:03 -0700, Hua Zhong wrote:
> >>>#if KILLER == 1
> >>>#define MACRO
> >>>#else
> >>>#define MACRO do { } while (0)
> >>>#endif
> >>>
> >>>{
> >>> if (some_condition)
> >>> MACRO
> >>>
> >>> if_this_is_not_called_you_loose_your_data();
> >>>}
> >>>
> >>>How do you want to define KILLER, 0 or 1? I personally choose 0.
> >>Really? Does it compile?
> >
> >No, and that is the whole point.
> >
> >The empty 'do {} while (0)' makes the missing semicolon a syntax error.
>
> Bulls^WNope, it was a bad example (we don't want to break the compilation,
> just not want to emit a warn or an err).
Your sentence does not make sense, but I'm going to take it as saying
that you disagree that the above will cause a syntax error. Try it:
$ cat t.c
#if KILLER == 1
#define MACRO
#else
#define MACRO do { } while (0)
#endif
void foo(int some_condition)
{
if (some_condition)
MACRO
if_this_is_not_called_you_loose_your_data();
}
$ gcc -O2 -o - -E t.c
# 1 "t.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "t.c"
void foo(int some_condition)
{
if (some_condition)
do { } while (0)
if_this_is_not_called_you_loose_your_data();
}
$ gcc -O2 -o - -S t.c >/dev/null
t.c: In function `foo':
t.c:12: error: parse error before "if_this_is_not_called_you_loose_your_data"
$ gcc -O2 -o - -E t.c -DKILLER
# 1 "t.c"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "t.c"
void foo(int some_condition)
{
if (some_condition)
if_this_is_not_called_you_loose_your_data();
}
$ gcc -O2 -o - -S t.c -DKILLER >/dev/null
$
Hence, using do { } while (0) has had the desired effect - the missing
semicolon causes a compile error, while the empty macro results in
unintentional successful compilation without warning or error.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 Serial core
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
