Hello Jon, On Mon, Aug 10, 2009 at 2:06 PM, Jon Grant <jg@xxxxxxxx> wrote: > Hello > > 2009/8/7 Michael Kerrisk <mtk.manpages@xxxxxxxxxxxxxx>: >> Jon, >> >> On Fri, Aug 7, 2009 at 1:55 PM, Jon Grant<jg@xxxxxxxx> wrote: >>> Looking at this man page: >>> >>> http://linux.die.net/man/3/strlen >>> >>> Should it not mention that a NULL address is a valid param? Or is it >>> not a valid param? >> >> What makes you think it is a valid parameter? > > NULL points to 0x0, which could be mapped to something. D'oh! Sorry -- now I'm with you. Yes, it could. > On my embedded > platform it is the beginning of the boot ROM. However typically 0x0 is > an invalid address, in which case strlen should check for NULL, and > return 0 I don't think it should check for this. If the addres is invalid, it should be treated like any other invalid address -- usually a SIGSEGV results. > e.g.: > > size_t strlen(const char *str) > { > const char *s; > > if(str == NULL) > { > return 0; > } > > for (s = str; *s; ++s) > ; > return (s - str); > } > >>> On most systems NULL is a special error pointer. >> >> I don't understand what you mean with this last sentence. Please explain. > > Well, the purpose of strlen is to count chars (excluding terminating > '\0') but on most systems address 0x0 [which is what NULL is, (void*)0 > ]. > > So if something is mapped by the hardware at 0x0 address then strlen > could be used to count the number of characters at that location. > However, on most systems his 0x0 address (NULL) indicates an invalid > address. > > I am not on this mailing list, so please keep my email address in any replies. As far as I can see, there's nothing in the documentation that needs to be fixed. I'm doubtful that glibc's strlen() should be fixed either. I agree that mappings at 0x0 are a strange corner case that can produce unusual results in cases like these. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Watch my Linux system programming book progress to publication! http://blog.man7.org/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
