Date: Wed, 10 Oct 2001 20:16:27 +0400 (MSD) From: "Andrew L. Neporada" <andrew@nas.dgap.mipt.ru> To: Mike Barcroft <mike@FreeBSD.ORG> Cc: audit@FreeBSD.ORG Subject: Re: strnstr(3) - New libc function for review Message-ID: <Pine.BSF.4.21.0110101958250.51458-200000@nas.dgap.mipt.ru> In-Reply-To: <20011010115210.E49828@coffee.q9media.com>
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[-- Attachment #1 --]
On Wed, 10 Oct 2001, Mike Barcroft wrote:
> [-hackers removed from CC]
>
> Andrew L. Neporada <andrew@nas.dgap.mipt.ru> writes:
> > I think you should write in ststr.3 that strnstr locates first occurrence
> > of null-terminated string 'little' in ___null-terminated___ string 'big'.
>
> No, that's inconsistent with existing strn...() functions and totally
> defeats the purpose of my addition.
>
Check attached test program. It prints "NULL". So either implementation or
man page is wrong.
> To quote from my patch:
> : Add a new libc function, strnstr(3), which allows one to limit the
> : number of characters that are searched. This is especially useful
> : with file operations and non-NUL terminated strings.
>
> > P.S. Because str(n)str functions deal with null-terminated strings
> > (i.e. we don't know sizes of strings), it is impossible to write
> > algorithm, that will work faster (in average) than current implementation.
>
> See above.
>
> > P.P.S. In the case of binary strings it is possible to implement faster
> > search -- see attachment.
>
> Yes.
Could you please comment my bstrstr implementation?
>
>
> Best regards,
> Mike Barcroft
>
Andrew.
[-- Attachment #2 --]
#include <string.h>
#include <stdio.h>
/*
* Find the first occurrence of find in s, where the search is limited to the
* first slen characters of s.
*/
char *
strnstr(s, find, slen)
const char *s;
const char *find;
size_t slen;
{
char c, sc;
size_t len;
if ((c = *find++) != '\0') {
len = strlen(find);
do {
do {
if ((sc = *s++) == '\0' || slen-- < 1)
return (NULL);
} while (sc != c);
if (len > slen)
return (NULL);
} while (strncmp(s, find, len) != 0);
s--;
}
return ((char *)s);
}
int
main(void)
{
char str[10] = {'a', 'b', 'c', '\0', 'a', 'b', 'c', 'd', 'e', 'f'};
char *pat = "abcd";
char *ptr;
ptr = strnstr(str, pat, 10);
if (ptr == NULL)
printf("NULL\n");
else
printf("%s\n");
exit(0);
}
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