That's not actually correct in practice. If you'd like to see that I'm
correct take the following two programs:
foo.c:
#include
#include
int main(int argc, char *argv[]) {
if (strlen(argv[0]) == 0) {
printf("Command empty");
} else {
printf("Command not empty");
}
}
bar.c:
#include
#include
int main(int argc, char *argv[]) {
if (*argv[0] == '\0') {
printf("Command empty");
} else {
printf("Command not empty");
}
}
Next compile them to assembly like so:
for f in {foo,bar}.c; do gcc -O2 -S $f; done
And then compare them:
diff {foo,bar}.s
They should be the same (possibly different by a ".file" line). And if you
inspect the resulting code, there won't be a call to strlen or to any
function at all (well, except printf).
The reason is that gcc, like most C compilers since the 90s, optimises a
number of common functions in the standard C library. Which means that
developers can stick with writing code that will be well-optimised *and*
highly readable.
Kevin
On Thu, Oct 5, 2017 at 8:31 PM Roy Marples wrote:
> On 05/10/2017 03:23, Rosen Penev wrote:
> > @@ -1239,7 +1238,7 @@ static struct serverfd *allocate_sfd(union
> mysockaddr *addr, char *intname)
> > #endif
> > }
> >
> > - if (intname && strlen(intname) != 0)
> > + if (!strlen(intname))
> > ifindex = if_nametoindex(intname); /* index == 0 when not binding
> to an interface */
> >
> > /* may have a suitable one already */
> >
>
> I have no comment on the functionality of the patch (it if intname needs
> to be NULL checked or not), but this is not a good use of strlen.
>
> This could be re-written as
>
> if (*intname != '\0')
>
> Which saves a function call because the actual length of the string is
> not used.
>
> Roy
>
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