Re: [MLUG] String manipulation in C

[Stephen Montgomery-Smith <EMAIL:PROTECTED>]

On Sun, 1 Jul 2007, Stephen Montgomery-Smith wrote:

> On Sun, 1 Jul 2007, Jack Smith wrote:
>
> > I have a little problem that you guys might be able to solve. I am
> > trying to find out where a short sequence of letters matches in a much
> > longer sequence of letters. I can find the location of the first match,
> > but I cannot make it find any subsequent matches and need to. After
> > reading the GNU regex documentation, I don't think that the regexec()
> > function searches beyond one match of pattern in string.
> >
> > So what I'd like to do is hack everything off of the first string after
> > the end of the first match. If I am looking for "ABC" in the following
> > string:
> >
> >     XXXXXABCXXXXXABCXX
> >
> > I'd like to reduce the string to
> >
> >    XXXXXABCXX
> >
> > after the first "ABC" is found so that the second match can be found. I
> > cannot find a function that will copy the last n digits of a string into
> > an array (sort of an opposite to strncpy()) so that I could simply
> > cleave out anything before and including the match in string, then
> > search the remainder.
> >
> > Any help would be appreciated.
>
> This is actually much easier than you think.  If the string s (which is 
> actually a pointer) contains
> "abcdefgh"
> then the string s+4 contains
> "efgh"
> So just put s+4 into your search function instead of s.  No copying needed 
> (although if you wanted to copy it, just put s+4 into strncpy or strcpy or 
> whatever).

Also you might want to look at the function strstr instead of regexec. 
For what you are wanting to do, it looks a lot simpler.  So suppose you 
are looking for the third occurence of "ABC" in "XXABCXXABCXXABCXXX":

char *s, *t, *u;

strcpy(s,"ABC");
strcpy(t,"XXABCXXABCXXABCXXX");
u = strstr(t,s);
if (u!=NULL) u = strstr(u,s);
if (u!=NULL) u = strstr(u,s);
if (u!=NULL) printf("%d\n",u-s); else printf("Not found");


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