Re: Find a string in another string
 

"MM" <dobedidoo@yahoo.se> wrote:

> For example, if I look for the string "searchString" in the string "jlh ahs
> dalskd" then it is of course NOT found, but if I instead look for the same
> string in "lkasjalskj searchString sedlfksd" then it IS found.

Erm... what about strstr()?

Richard

Find a string in another string
 

Hello there

I need a way to efficiently check if a string I specify can be found in
another string.

For example, if I look for the string "searchString" in the string "jlh ahs
dalskd" then it is of course NOT found, but if I instead look for the same
string in "lkasjalskj searchString sedlfksd" then it IS found.

So, is there any (fairly) efficient way to do this?

Many thanks in advance,

MM

Re: Find a string in another string
 

On Mon, 11 Aug 2003 15:39:41 +0200, "MM" <dobedidoo@yahoo.se> wrote:

>Hello there
>
>I need a way to efficiently check if a string I specify can be found in
>another string.

strstr(), although I can't vouch for it's efficiency on your platform


--
Lew Pitcher
IT Consultant, Enterprise Technology Solutions
Toronto Dominion Bank Financial Group

(Opinions expressed are my own, not my employers')

Re: Find a string in another string
 

MM wrote:
>
> Hello there
>
> I need a way to efficiently check if a string I specify can be found in
> another string.
>
> For example, if I look for the string "searchString" in the string "jlh ahs
> dalskd" then it is of course NOT found, but if I instead look for the same
> string in "lkasjalskj searchString sedlfksd" then it IS found.
>
> So, is there any (fairly) efficient way to do this?

The C language Standard makes no guarantees -- indeed,
it says nothing at all -- about the efficiency of any
construct or library function. Still, a few guidelines:

- If you're doing just a few such searches, use
the strstr() function

- If you're doing many searches using the same
"SearchString" in different target strings,
implement something like the Bayer-Moore
algorithm

- If you're doing many searches using different
"SearchString"s in the same target string,
implement something like Patricia (see Knuth
TAOCP Volume III)

- If you're doing many searches using different
"SearchStrings" *and* different target strings,
use the strstr() function

.... but in no case should you go to the effort of Bayer-Moore
or Patricia until you've *measured* your program's performance
and *proven* to yourself that searching for strings within
strings takes unacceptably long. Start with strstr() and
adopt fancier solutions only if they're proven necessary --
and even then, it might turn out that the "best" approach
is to re-think the program design to obviate the searches.

--
Eric.Sosman@sun.com

Re: Find a string in another string
 

"Richard Bos" <rlb@hoekstra-uitgeverij.nl> wrote in message
news:3f377d9a.2240582727@news.nl.net...
> "MM" <dobedidoo@yahoo.se> wrote:
>
> > For example, if I look for the string "searchString" in the string "jlh
ahs
> > dalskd" then it is of course NOT found, but if I instead look for the
same
> > string in "lkasjalskj searchString sedlfksd" then it IS found.
>
> Erm... what about strstr()?
>
> Richard

Ah, looks nice and simple. Thanks!

And if I want to use for example strstr() to search for a substring in only
the first n characters of the "main" string? I want to do something like
this (although this does not work, of course, since mainString[1..n] is not
the correct way to "cut" a string):

pos = strstr(mainString[1..n],searchString);

//MM

Re: Find a string in another string
 

In <K1OZa.3628$Y5.1008@nntpserver.swip.net> "MM" <dobedidoo@yahoo.se> writes:


>"Richard Bos" <rlb@hoekstra-uitgeverij.nl> wrote in message
>news:3f377d9a.2240582727@news.nl.net...
>> "MM" <dobedidoo@yahoo.se> wrote:
>>
>> > For example, if I look for the string "searchString" in the string "jlh
>ahs
>> > dalskd" then it is of course NOT found, but if I instead look for the
>same
>> > string in "lkasjalskj searchString sedlfksd" then it IS found.
>>
>> Erm... what about strstr()?
>>
>And if I want to use for example strstr() to search for a substring in only
>the first n characters of the "main" string? I want to do something like
>this (although this does not work, of course, since mainString[1..n] is not
>the correct way to "cut" a string):
>
> pos = strstr(mainString[1..n],searchString);

If mainString is writable, temporarily replace mainString[n] by a null
character. Restore it after the strstr call. Otherwise, make a copy of
the first n characters of mainString and use it instead. C has no syntax
for specifying substrings.

It's much simpler to specify the "tail" of a C string: mainString + n
means the string containing everything but the first n characters of
mainString.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

Re: Find a string in another string
 

In article <3F37AB60.196F394E@sun.com>
Eric Sosman <Eric.Sosman@Sun.COM> writes:
>... but in no case should you go to the effort of Bayer-Moore
>or Patricia until you've *measured* your program's performance
>and *proven* to yourself that searching for strings within
>strings takes unacceptably long. ...

Right. But note that one will have better luck searching for the
correct name, "Boyer-Moore". :-) (The respelled name *does* appear
to be in at least somewhat common use, but Bob Boyer's name really
is spelled "Boyer", not "Bayer". See
<http://www.cs.utexas.edu/users/moore/best-ideas/string-searching/>
for instance.)
--
In-Real-Life: Chris Torek, Wind River Systems (BSD engineering)
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W) +1 801 277 2603
email: forget about it http://67.40.109.61/torek/index.html (for the moment)
Reading email is like searching for food in the garbage, thanks to spammers.

Re: Find a string in another string
 

In article <s0NZa.3623$Y5.1025@nntpserver.swip.net>, MM wrote:
> Hello there
>
> I need a way to efficiently check if a string I specify can be found in
> another string.
>
> For example, if I look for the string "searchString" in the string "jlh ahs
> dalskd" then it is of course NOT found, but if I instead look for the same
> string in "lkasjalskj searchString sedlfksd" then it IS found.
>
> So, is there any (fairly) efficient way to do this?
[-]
More than one 8-)

You C library'd provide strstr(), which is often based on or
implented as the Boyer-Moore algorithm. If your strings to
be searched in are very short or very long other methods might
be more efficient, so if you can time a test application to see
whether (your) strstr() is good enough for your problem.

Ta',
Juergen

--
\ Real name : Juergen Heinzl \ no flames /
\ EMail Private : juergen@manannan.org \ send money instead /

Re: Find a string in another string
 

"Eric Sosman" <Eric.Sosman@sun.com> wrote in message
news:3F37AB60.196F394E@sun.com...

(snip)

> ... but in no case should you go to the effort of Bayer-Moore
> or Patricia until you've *measured* your program's performance
> and *proven* to yourself that searching for strings within
> strings takes unacceptably long. Start with strstr() and
> adopt fancier solutions only if they're proven necessary --
> and even then, it might turn out that the "best" approach
> is to re-think the program design to obviate the searches.

Unless, of course, this is a homework assignment to use such an algorithm.

-- glen