Messages in this thread | | | Date | Fri, 23 May 2008 22:42:28 +0200 | From | Willy Tarreau <> | Subject | Re: kernel coding style for if ... else which cross #ifdef |
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On Fri, May 23, 2008 at 02:11:43PM -0500, Steve French wrote: > A question splitting "else" and "if" on distinct lines vs. using an > extra line and extra #else came up as I was reviewing a proposed cifs > patch. Which is the preferred style? > > #ifdef CONFIG_SOMETHING > if (foo) > something ... > else > #endif > if ((mode & S_IWUGO) == 0) > > or alternatively > > #ifdef CONFIG_SOMETHING > if (foo) > something ... > else if ((mode & S_IWUGO) == 0) > #else > if ((mode & S_IWUGO) == 0) > #endif
The second one is dangerous because if code evolves, chances are that only one of the two identical lines will be updated.
At least the first one is clearly readable. But if you have tons of places with the same construct, it's better to create a macro which will inhibit the if branch, which gcc will happily optimize away. For instance :
#ifdef CONFIG_FOO #define FOO_ENABLED 1 #else #define FOO_ENABLED 0 #endif
if (FOO_ENABLED && foo) something else if ((mode & S_IWUGO) == 0) ...
One variant includes :
#ifdef CONFIG_FOO #define FOO_COND(x) (x) #else #define FOO_COND(x) 0 #endif
if (FOO_COND(foo)) something else if ((mode & S_IWUGO) == 0) ...
Regards, Willy
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