Date: Tue, 30 Sep 2008 15:55:26 -0400 From: "Ryan Stone" <rysto32@gmail.com> To: freebsd-current@freebsd.org Subject: Possible alternate definition of CTASSERT to allow its use in header files Message-ID: <bc2d970809301255n2a4517b0m88104462e40fb211@mail.gmail.com>
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This was prompted by some recent check-ins removing CTASSERTs from header files to prevent spurious errors from popping up. For example, this check-in: http://lists.freebsd.org/pipermail/cvs-src/2008-September/095328.html I've come up with an alternate definition of CTASSERT that can be used in header files. It works on gcc 3.4.6, 4.0.2 and 4.3.0(the only compilers I have quick access to). $ cat /tmp/tmp.c // New definition #define NEWASSERT(x) _NEWASSERT(x, __LINE__) #define _NEWASSERT(x, line) __NEWASSERT(x, line) #define __NEWASSERT(x, line) extern int __assert_ ## line [ x ? 1 : -1 ]; //existing BSD implementation #define CTASSERT(x) _CTASSERT(x, __LINE__) #define _CTASSERT(x, y) __CTASSERT(x, y) #define __CTASSERT(x, y) typedef char __assert ## y[(x) ? 1 : -1] CTASSERT(1); // line 11 CTASSERT(0); // line 12 CTASSERT(1); CTASSERT(0); // line 13 NEWASSERT(1); // line 16 NEWASSERT(0) ; // line 17 NEWASSERT(1); NEWASSERT(0); // line 18 NEWASSERT(1); NEWASSERT(1); // line 19 $ gcc -v -c /tmp/tmp.c -Wall -Werror /tmp/tmp.c:12: error: size of array `__assert12' is negative /tmp/tmp.c:13: error: size of array `__assert13' is negative /tmp/tmp.c:13: error: redefinition of typedef '__assert13' /tmp/tmp.c:13: error: previous declaration of '__assert13' was here /tmp/tmp.c:17: error: size of array `__assert_17' is negative /tmp/tmp.c:18: error: size of array `__assert_18' is negative $ Note that the compiler doesn't complain about multiple definitions of __assert18 and __assert19 like it does about the multiple definitions of __assert13, which is the reason that CTASSERTs can't be used in header files. Thoughts? Will this work on compilers other than gcc?help
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