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RE: Unomitted frame pointers
- From: "Sam Lauber" <sam124 at operamail dot com>
- To: "Dave Korn" <dave dot korn at artimi dot com>, gcc at gcc dot gnu dot org
- Date: Sat, 11 Dec 2004 03:44:45 +0100
- Subject: RE: Unomitted frame pointers
We would end up with two copies of the string. #defines are preprocessed, so it would expand to the second thing. The _safe_ way to do it is
char str = "Hello World!\n";
write(2, str, strlen(str)-1);
Then we can be sure that it refers to the same physical address in RAM. "Two copies" is when the strings are positioned at diffrent non-overlapping addresses. Though optimization and inlining might mess it up.
Samuel Lauber
----- Original Message -----
From: "Dave Korn" <dave.korn@artimi.com>
To: "'jlh'" <jlh@gmx.ch>, "'Thomas R. Truscott'" <trt@cs.duke.edu>
Subject: RE: Unomitted frame pointers
Date: Fri, 10 Dec 2004 16:23:59 -0000
>
> > -----Original Message-----
> > From: gcc-owner On Behalf Of jlh
> > Sent: 10 December 2004 16:05
> > To: Thomas R. Truscott
>
> > > Off-topic, but the hello.c program does:
> > > write(2, "Hello World!\n\0", 16);
> > > The string length is 15, not 16.
> >
> > 15 is what gets allocated for storing the string (counting
> > the additional \0 that always gets appened to string constants).
> > But neither the explicit nor the implicit \0 should be printed
> > to the console, so the call should definitely read:
> >
> > write(2, "Hello World!\n", 13);
> >
> > jlh
>
>
> Except of course on targets where '\n' expands to a two char CR-LF
> combination.
>
> So really the safe way to code this is
>
> #define HELLOSTRING "Hello World!\n"
>
> write (2, HELLOSTRING, strlen(HELLOSTRING)-1);
>
> and let the compiler statically compute the string length for you at
> compiletime. The #define is used to make sure we don't end up with two copies
> of the string that get out of sync, as would be bound to happen
> sooner or later
> if we wrote
>
> write (2, "Hello World!\n", strlen("Hello World!\n")-1);
>
> cheers,
> DaveK
> --
> Can't think of a witty .sigline today....
--
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