Messages in this thread | | | Subject | Re: [PATCH v3 04/14] lib/vsprintf.c: expand field_width to 24 bits | From | Joe Perches <> | Date | Thu, 03 Dec 2015 16:03:02 -0800 |
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On Thu, 2015-12-03 at 15:34 -0800, Andrew Morton wrote: > I've been fiddling with a BUILD_BUG_ON which works outside functions > using gcc's __COUNTER__ - something like > > #define BBO(expr) typedef char __bbo##__COUNTER__[1-2*(!!expr)]
nit: you need another parenthesis around expr
> BBO(1 == 1); > BBO(2 == 2); > > but that comes out as > > typedef char __bbo__COUNTER__[1-2*(!!1 == 1)]; > typedef char __bbo__COUNTER__[1-2*(!!2 == 2)]; > > instead of > > typedef char __bbo0[1-2*(!!1 == 1)]; > typedef char __bbo1[1-2*(!!2 == 2)]; > > There's some trick here but I've forgotten what it is.
I believe it's something like:
#define __stringify_2(a, b) a##b #define __stringify2(a, b) __stringify_2(a, b)
#define BBO(expr) typedef char __stringify2(bbo, __COUNTER__)[1 - 2*(!!(expr))]
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