On Thu, 2009-11-12 at 16:33 +0100, Julia Lawall wrote: > On Thu, 12 Nov 2009, Bernd Petrovitsch wrote: > > > On Thu, 2009-11-12 at 08:49 +0100, Julia Lawall wrote: > > > From: Julia Lawall <julia@xxxxxxx> > > > > > > As observed by Joe Perches, sizeof of a constant string includes the > > > trailing 0. If what is wanted is to check the initial characters of > > > another string, this trailing 0 should not be taken into account. If an > > > exact match is wanted, strcmp should be used instead. > > [...] > > > strncmp(foo, abc, > > > - sizeof(abc) > > > + sizeof(abc)-1 > > > ) > > > // </smpl> > > Am I the only one who find "strlen()" instead of "sizeof()-1" here much > > more readable (and to the point). > > > > As for run-time, it shouldn't make a difference for static/constant > > strings as gcc should be able calculate the length at compile time. And > > if the string is not constant, sizeof() is probably wrong anyways. > > Does gcc have access to the definition of strlen? It does not seem to be > an inlined function, eg in lib/string.c. Since "strlen()" is defined in the C-Standard C-compilers could rely on the defined behaviour (but I don't know exactly how gcc behaves with -ffreestanding for all supported versions). Then there is __builin_strlen() (see also http://gcc.gnu.org/onlinedocs/gcc-4.4.2/gcc/Other-Builtins.html#Other-Builtins). Stepping a quite small abstraction layer higher: include/linux/string.h has at teh end: ---- snip ---- static inline bool strstarts(const char *str, const char *prefix) { return strncmp(str, prefix, strlen(prefix)) == 0; } ---- snip ---- seems to be what most uses of strnmcp() actually are: check if one string is a prefix of another. Bernd -- Firmix Software GmbH http://www.firmix.at/ mobil: +43 664 4416156 fax: +43 1 7890849-55 Embedded Linux Development and Services -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
