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From:   Andreas Schwab <schwab@linux-m68k.org>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Joe Perches <joe@perches.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Tom Zanussi <zanussi@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [for-next][PATCH 23/24] string.h: Add strncmp_prefix() helper macro
References: <20181221175618.968519903@goodmis.org>
        <20181221175659.208858193@goodmis.org>
        <CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com>
        <20181221144054.20bdeb33@gandalf.local.home>
        <CAHk-=wgSvRhj6KNRdn9gbK9RJVAswdtKSNjAxdf9O9vn04T5XQ@mail.gmail.com>
        <20181221153526.5e6055ca@gandalf.local.home>
        <077eeb8b09baebe78822819b5f15d671b738a2b2.camel@perches.com>
        <20181221155435.38a9a221@gandalf.local.home>
Date:   Fri, 21 Dec 2018 21:58:32 +0100
In-Reply-To: <20181221155435.38a9a221@gandalf.local.home> (Steven Rostedt's
        message of "Fri, 21 Dec 2018 15:54:35 -0500")
Message-ID: <871s6ad2br.fsf@igel.home>
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On Dez 21 2018, Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 21 Dec 2018 12:46:47 -0800
> Joe Perches <joe@perches.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@linux-m68k.org
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