Re: [PATCH 8/10] bug.h: Make BUILD_BUG_ON generate compile-time error

Daniel Santos
2012-09-30T23:29:03Z

On 09/28/2012 09:55 PM, Josh Triplett wrote:
> Assuming you don't call BUILD_BUG_ON_MSG more than once per line:
>
> /tmp$ cat test.c
> #define BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line) \
> do { \
> extern void __build_bug_on_failed_ ## line (void) __attribute__((error(msg))); \
> if (cond) \
> __build_bug_on_failed_ ## line(); \
> } while (0)
>
> #define BUILD_BUG_ON_MSG_INTERNAL(cond, msg, line) BUILD_BUG_ON_MSG_INTERNAL2(cond, msg, line)
> #define BUILD_BUG_ON_MSG(cond, msg) BUILD_BUG_ON_MSG_INTERNAL(cond, msg, __LINE__)
>
> void f(void)
> {
> BUILD_BUG_ON_MSG(0, "test 1");
> BUILD_BUG_ON_MSG(1, "test 2");
> BUILD_BUG_ON_MSG(0, "test 3");
> BUILD_BUG_ON_MSG(1, "test 4");
> }
> /tmp$ gcc -c test.c
> test.c: In function ‘f’:
> test.c:14:119: error: call to ‘__build_bug_on_failed_14’ declared with attribute error: test 2
> test.c:16:119: error: call to ‘__build_bug_on_failed_16’ declared with attribute error: test 4
Thanks! This is very nice! I've done a little more research and
discovered that there's also a __COUNTER__ macro that is available
in gcc 4.3+. Before I realized that it was only available in gcc
4.3, I wrote this little macro:

#define _CONCAT1(a, b) a##b
#define CONCAT(a, b) _CONCAT1(a, b)

#ifdef __COUNTER__
# define UNIQUIFY(prefix) CONCAT(prefix, __COUNTER__)
#else
# define UNIQUIFY(prefix) CONCAT(prefix, __LINE__)
#endif

However, this could lead to code might compile on gcc 4.3+, but
not compile prior, so this is bad, right?

Daniel