NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/lang/c/18340

Text File | 1992-12-14 | 2.6 KB | 54 lines

Newsgroups: comp.lang.c
Path: sparky!uunet!zaphod.mps.ohio-state.edu!caen!hellgate.utah.edu!lanl!cochiti.lanl.gov!jlg
From: [e-mail] (J. Giles)
Subject: Re: No, but strncat() is stupid (was: definition of strncpy stupid?)
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Los Alamos National Laboratory
References: <[e-mail]>  <[e-mail]> <[e-mail]>
Date: Mon, 14 Dec 1992 19:09:36 GMT
Lines: 42

In article <[e-mail]>, [e-mail] (Brett Kottmann) writes:
|> In article <[e-mail]>, [e-mail] (J. Giles) writes:
|> > I can't simply say
|> >
|> >    strncat(s1,s2,N);
|> >
|> > This would *add* N characters to s1, not limit it's total length
|> > to N.  In order to do what I want, I have to:
|> >
|> >    strncat(s1, s2, N - strlen(s1));
|> >
|> > Except, I can't do this either.  Previous operations on s1 may
|> > have left it without null termination - so strlen() won't work.
|>
|>     It better have null termination.  strncat uses that to start storing
|> s2.

You've missed my point.  If the length of `s1' is equal to `N', there is
no room for null termination.  Therefore `s1' will not have it.  No matter,
the amount I want strncat to move in that case it zero characters.  So,
strncat() will not have to find any null termination of `s1'.  I was
pointing out the same thing you were - only one step earlier.  Since
`s1' may not be null terminated (it can't be if there's no room), then
strlen() won't work on it.  Of course, you could pretend the allocated
length was one character shorter than it actually was and insure that
there was always room for a terminating null.  That still doesn't solve
the problem that you have to do all the calculations yourself in order
to make sure that you don't run past the end : you still have to do the
redundant `N-strlen(s1)' expression.

Personally, I think that null termination is a bad idea anyway, and
when I have to do character manipulation in C, I use the mem***()
functions exclusively.  In fact, all the character variables I
declare are structs which explicitly carry the present length, the
allocated length, and the pointer to the actual string.  I then use
string manipulation functions of my own (which use the mem***() stuff)
that automatically maintain the information in the struct.  This is
almost *always* faster than the str***() or the strn***() functions
and is certainly safer.

--
J. Giles