Re: [PATCH 2/2] Replace literal STRLEN_ #defines in refs.h with compiler evaluated expressions

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Sep 29, 2007, 18:15 UTC
Message-ID: <alpine.LFD.0.999.0709291103380.3579@woody.linux-foundation.org>
In-Reply-To: <7vd4w1l872.fsf@gitster.siamese.dyndns.org>

On Sat, 29 Sep 2007, Junio C Hamano wrote:

Show 6 quoted lines

> 
> I do not think the above is wrong per se, but doesn't a good
> compiler optimize
> 
> 	#define PATH_REMOTES	"remotes/"
> 	#define STRLEN_PATH_REMOTES strlen(PATH_REMOTES)

Gcc does, yes.

HOWEVER.

Using "strlen()" may be optimized at compile-time, but it still ends up resulting in illegal C code if the constant needs to be a constant in the semantic sense.

IOW, the "sizeof()" trick can be portably used for things like array declarations etc. But strlen() cannot. Ie

	char array[sizeof("hello")-1];

is legal in non-function scope, but doing the same with "strlen()" is not.

(That said, gcc has been known to accept bad C code, and will in fact accept this one too!)

		Linus