linux-kernel - Re: [for-next][PATCH 23/24] string.h: Add strncmp

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Date:   Fri, 21 Dec 2018 21:58:32 +0100
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Joe Perches <joe@...ches.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper macro

On Dez 21 2018, Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 21 Dec 2018 12:46:47 -0800
> Joe Perches <joe@...ches.com> wrote:
>
>> > + * @str: The string to test
>> > + * @prefix: The string to see if @str starts with
>> > + *
>> > + * A common way to test a prefix of a string is to do:
>> > + *  strncmp(str, prefix, sizeof(prefix) - 1)
>> > + *
>> > + * But this can lead to bugs due to typos, or if prefix is a pointer
>> > + * and not a constant. Instead use has_prefix().
>> > + *
>> > + * Returns: 0 if @str does not start with @prefix
>> > +         strlen(@prefix) if @str does start with @prefix
>> > + */
>> > +#define has_prefix(str, prefix)						\
>> > +	({								\
>> > +		const char *____prefix____ = (const char *)(prefix);	\
>> > +		int ____len____ = strlen(____prefix____);		\
>> > +		strncmp(str, ____prefix____, ____len____) == 0 ?	\
>> > +			____len____ : 0;				\
>> > +	})   
>> 
>> I think all the underscores are unnecessary and confusing.
>> 
>
> Well, perhaps I can just remove the ending ones. I get paranoid with
> macro variables, and tend to over do it so that there's no question.

Why not make it an inline function?

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
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