Date: Wed, 07 Feb 2001 21:11:43 -0500 (EST) From: Mike Heffner <mheffner@vt.edu> To: "Jacques A. Vidrine" <n@nectar.com> Cc: FreeBSD-audit <FreeBSD-audit@FreeBSD.ORG>, Warner Losh <imp@harmony.village.org> Subject: Re: lam(1) patch Message-ID: <XFMail.20010207211143.mheffner@vt.edu> In-Reply-To: <20010207180825.A85807@spawn.nectar.com>
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Even though our implementation is inlined, I think I'll take Warner's
suggestion so that it's clear. As I found out in the following, it wasn't what
I would have expected:
#define xtolower(c) ((c) + 0x20 * (((c) >= 'A') && ((c) <= 'Z')))
int
main(int ac, char **av)
{
char *c, *p = "HELLO";
switch(xtolower(*(c = ++p))) {
default:
printf("Char: '%c'\n", *c);
}
printf("String: '%s'\n", p);
}
[spock@enterprise]:117 $ ./test
Char: 'L'
String: 'LO'
On 08-Feb-2001 Jacques A. Vidrine wrote:
| On Wed, Feb 07, 2001 at 04:18:45PM -0700, Warner Losh wrote:
|> The tolower function will only evaluate the arguments once, but the
|> tolower macro might evaluate them multiple times. Maybe I'm recalling
|> things too far back.
|
| C99 7.1.4.1 says, ``Any invocation of a library function that is
| implemented as a macro shall expand to code that evaluates each of its
| arguments exactly once, fully protected by parentheses where necessary,
| so it is generally safe to use arbitrary expressions as arguments.''
|
| Our tolower is implemented as an inline.
|
| I'd like to know when this was first spelled out -- I don't have a
| C89 reference handy.
|
| Cheers,
| --
| Jacques Vidrine / n@nectar.com / jvidrine@verio.net / nectar@FreeBSD.org
|
|
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--
Mike Heffner <mheffner@vt.edu>
Blacksburg, VA <mikeh@FreeBSD.org>
http://filebox.vt.edu/users/mheffner
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