Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #42471

Re: array-size/malloc limit and strlen() failure

Show all headers | View raw

"BartC" <bc@freeuk.com> writes:
[...]
> I doubt strlen will do much error checking, and I don't see how it can. It 
> will expect the input to be well-formed, that is, it expects to encounter a 
> 0-byte before it hits the end of the memory block, and before it wraps the 
> address space. It can't know the size of the memory block, and it would be 
> too slow to keep checking that it runs out of address space as well as 
> looking for a zero byte.
>
> However, you can write your own strlen() function which takes some of that 
> into account, if you're that paranoid about it (although beware that if the 
> address space is 64-bits, wrap-around might be impossible).

You can't *portably* write such a strlen() function.  There is no
portable way to tell whether a given non-null address is valid or not.

In any case, strlen isn't the problem here.  If you can allocate an
array and ensure that it contains a null byte somewhere, you can run
strlen on it.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

array-size/malloc limit and strlen() failure jay <arnuld.mizong@gmail.com> - 2014-04-01 23:31 -0700
  Re: array-size/malloc limit and strlen() failure Xavier Roche <xroche@free.fr.NOSPAM.invalid> - 2014-04-02 08:47 +0200
  Re: array-size/malloc limit and strlen() failure Kaz Kylheku <kaz@kylheku.com> - 2014-04-02 07:36 +0000
  Re: array-size/malloc limit and strlen() failure "BartC" <bc@freeuk.com> - 2014-04-02 10:10 +0100
    Re: array-size/malloc limit and strlen() failure Keith Thompson <kst-u@mib.org> - 2014-04-02 08:11 -0700
      Re: array-size/malloc limit and strlen() failure glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-02 19:03 +0000
        Re: array-size/malloc limit and strlen() failure James Kuyper <jameskuyper@verizon.net> - 2014-04-02 15:48 -0400
          Re: array-size/malloc limit and strlen() failure Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-02 14:42 -0700
            Re: array-size/malloc limit and strlen() failure Keith Thompson <kst-u@mib.org> - 2014-04-02 15:14 -0700
        Re: array-size/malloc limit and strlen() failure Keith Thompson <kst-u@mib.org> - 2014-04-02 14:55 -0700
          Re: array-size/malloc limit and strlen() failure glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-02 23:42 +0000
  Re: array-size/malloc limit and strlen() failure Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-02 02:34 -0700
  Re: array-size/malloc limit and strlen() failure James Kuyper <jameskuyper@verizon.net> - 2014-04-02 07:40 -0400
    Re: array-size/malloc limit and strlen() failure Thomas Jahns <jahns@idontlikespam.dkrz.de> - 2014-04-02 13:52 +0200
    Re: array-size/malloc limit and strlen() failure Keith Thompson <kst-u@mib.org> - 2014-04-02 08:21 -0700
      Re: array-size/malloc limit and strlen() failure James Kuyper <jameskuyper@verizon.net> - 2014-04-02 11:30 -0400
      Re: array-size/malloc limit and strlen() failure glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-02 19:26 +0000
        Re: array-size/malloc limit and strlen() failure "BartC" <bc@freeuk.com> - 2014-04-02 20:39 +0100
        Re: array-size/malloc limit and strlen() failure Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2014-04-02 14:39 -0600
        Re: array-size/malloc limit and strlen() failure Keith Thompson <kst-u@mib.org> - 2014-04-02 15:03 -0700
          Re: array-size/malloc limit and strlen() failure Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-03 01:11 -0700
            Re: array-size/malloc limit and strlen() failure Ike Naar <ike@iceland.freeshell.org> - 2014-04-03 14:27 +0000
              Re: array-size/malloc limit and strlen() failure James Kuyper <jameskuyper@verizon.net> - 2014-04-03 17:56 -0400
            Re: array-size/malloc limit and strlen() failure Keith Thompson <kst-u@mib.org> - 2014-04-03 08:18 -0700
              Re: array-size/malloc limit and strlen() failure gazelle@shell.xmission.com (Kenny McCormack) - 2014-04-03 15:30 +0000
      Re: array-size/malloc limit and strlen() failure Stephen Sprunk <stephen@sprunk.org> - 2014-04-03 00:33 -0500

csiph-web