need some help

[ash]

hi friends,
i have some questions whch is in my last year question papers.i need
some help to get logic of these questions.

1) write a C function, that takes two strings as arguments and returns
a pointer to the first occurrence of 1st string in 2nd string or NULL
if it is not present.

-- i tried to solve it but it seems that i am not understanding this
question at all.i am taking this question as:

1st string- "cat"
2nd string-"i like cat."

i have to return pointer that has strarting address of 'c' of cat of
2nd string.i can make a program ( that finds a string into another )
but how to return pointer of that string i don`t know.
please suggest some advice.

2) write a 'C' function
char **readAndcreate (int n)
the function reads "n" strings from the input and creates a list of
such strings dynamically using "malloc" library call.
-- as well as i understand i have to make a linked list that will hold
the strings(i can make it )but one thing i didn`t understand what this
function will return, Address of first node of that list or something
else.if yes please describe how?

my english is not good but i think you have understood my problems.if
anyone can suggest a good link related to my problems, i will be
thankful.
thankx in advance
:)

[Richard Heathfield]

Re: need some help

ash said:
[color=blue]
> hi friends,
> i have some questions whch is in my last year question papers.i need
> some help to get logic of these questions.
>
> 1) write a C function, that takes two strings as arguments and returns
> a pointer to the first occurrence of 1st string in 2nd string or NULL
> if it is not present.[/color]

Well, that one's easy, at any rate.

#include <string.h>
char *ashstrstr(char *haystack, char *needle)
{
return strstr(haystack , needle);
}
[color=blue]
> 2) write a 'C' function
> char **readAndcreate (int n)
> the function reads "n" strings from the input and creates a list of
> such strings dynamically using "malloc" library call.
> -- as well as i understand i have to make a linked list that will hold
> the strings(i can make it )but one thing i didn`t understand what this
> function will return, Address of first node of that list or something
> else.if yes please describe how?[/color]

If it were asking for a linked list, it would have said so, and there would
have been some kind of linked list thingy in the prototype, and it didn't
and there isn't so it isn't.

No, what it's looking for is this:

1) set up your array of n char * objects, like this:

char **new = malloc(n * sizeof *new);
if(new != NULL)
{

2) the next stage is to write (or find) a function that can read an entire
line from standard input, reallocating storage as and when necessary to
ensure that there is sufficient room to store the string. For a very simple
way to do this that will suit you very well, look for Chuck Falconer's
ggets() function which, last I heard, could be found at:

<http://cbfalconer.home .att.net/download/ggets.zip>

3) simply call this function in a loop, assigning each pointer thus obtained
to new[i], where i is your loop counter, running from 0 to n-1. What will
you do if the function returns NULL, to indicate insufficient storage, or
perhaps an absence of input data?

4) return new;


--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

[Fred Kleinschmidt]

Re: need some help


"Richard Heathfield" <invalid@invali d.invalid> wrote in message
news:dcqdncLBzs urHBTZRVnytQ@bt .com...[color=blue]
> ash said:
>[color=green]
>> hi friends,
>> i have some questions whch is in my last year question papers.i need
>> some help to get logic of these questions.
>>
>> 1) write a C function, that takes two strings as arguments and returns
>> a pointer to the first occurrence of 1st string in 2nd string or NULL
>> if it is not present.[/color]
>
> Well, that one's easy, at any rate.
>
> #include <string.h>
> char *ashstrstr(char *haystack, char *needle)
> {
> return strstr(haystack , needle);
> }[/color]

This is wrong. It should be strstr(needle, haystack).
The instruction was to find first occurence of s1 in s2.
strstr finds first s2 in s1.

For this homework, I think the instructor really wants
the student to write the internals of strstr. If so, he/she
should have explicitly stated that using strstr was not allowed.
[color=blue]
>[color=green]
>> 2) write a 'C' function
>> char **readAndcreate (int n)
>> the function reads "n" strings from the input and creates a list of
>> such strings dynamically using "malloc" library call.
>> -- as well as i understand i have to make a linked list that will hold
>> the strings(i can make it )but one thing i didn`t understand what this
>> function will return, Address of first node of that list or something
>> else.if yes please describe how?[/color]
>
> If it were asking for a linked list, it would have said so, and there
> would
> have been some kind of linked list thingy in the prototype, and it didn't
> and there isn't so it isn't.
>
> No, what it's looking for is this:
>
> 1) set up your array of n char * objects, like this:
>
> char **new = malloc(n * sizeof *new);
> if(new != NULL)
> {
>
> 2) the next stage is to write (or find) a function that can read an entire
> line from standard input, reallocating storage as and when necessary to
> ensure that there is sufficient room to store the string. For a very
> simple
> way to do this that will suit you very well, look for Chuck Falconer's
> ggets() function which, last I heard, could be found at:
>
> <http://cbfalconer.home .att.net/download/ggets.zip>
>
> 3) simply call this function in a loop, assigning each pointer thus
> obtained
> to new[i], where i is your loop counter, running from 0 to n-1. What will
> you do if the function returns NULL, to indicate insufficient storage, or
> perhaps an absence of input data?
>
> 4) return new;
>
>
> --
> Richard Heathfield
> "Usenet is a strange place" - dmr 29/7/1999
> http://www.cpax.org.uk
> email: rjh at above domain (but drop the www, obviously)[/color]
--
Fred L. Kleinschmidt
Boeing Associate Technical Fellow
Technical Architect, Software Reuse Project

[osmium]

Re: need some help

"Richard Heathfield" wrote:
[color=blue]
> ash said:
>[color=green]
>> hi friends,
>> i have some questions whch is in my last year question papers.i need
>> some help to get logic of these questions.
>>
>> 1) write a C function, that takes two strings as arguments and returns
>> a pointer to the first occurrence of 1st string in 2nd string or NULL
>> if it is not present.[/color]
>
> Well, that one's easy, at any rate.
>
> #include <string.h>
> char *ashstrstr(char *haystack, char *needle)
> {
> return strstr(haystack , needle);
> }[/color]

You know perfectly well that that is not what the instructor wanted.

[Richard Heathfield]

Re: need some help

Fred Kleinschmidt said:
[color=blue]
>
> "Richard Heathfield" <invalid@invali d.invalid> wrote in message
> news:dcqdncLBzs urHBTZRVnytQ@bt .com...[color=green]
>> ash said:
>>[color=darkred]
>>> hi friends,
>>> i have some questions whch is in my last year question papers.i need
>>> some help to get logic of these questions.
>>>
>>> 1) write a C function, that takes two strings as arguments and returns
>>> a pointer to the first occurrence of 1st string in 2nd string or NULL
>>> if it is not present.[/color]
>>
>> Well, that one's easy, at any rate.
>>
>> #include <string.h>
>> char *ashstrstr(char *haystack, char *needle)
>> {
>> return strstr(haystack , needle);
>> }[/color]
>
> This is wrong. It should be strstr(needle, haystack).[/color]

<sigh> The easy ones are always hardest.
[color=blue]
> The instruction was to find first occurence of s1 in s2.
> strstr finds first s2 in s1.[/color]

Quite right. My apologies.
[color=blue]
> For this homework, I think the instructor really wants
> the student to write the internals of strstr.[/color]

Yes, but here in comp.lang.c we try to get the OP to think, rather than
spoonfeed them a solution. In this case, I was trying to get him (or
possibly her - I haven't checked) to think about how to phrase the
question. Shame I messed up the answer, though...
[color=blue]
> If so, he/she
> should have explicitly stated that using strstr was not allowed.[/color]

Precisely so.

<snip>

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

[ash]

Re: need some help


one friend advised me to use "strstr" function, this is a easy way to
solve that question by use built in function but actually i was trying
to make this function and i want help in writing that function.

[ash]

Re: need some help


one friend advised me to use "strstr" function, this is a easy way to
solve that question by use built in function but actually i was trying
to make this function and i want help in writing that function.

[Default User]

Re: need some help

ash wrote:
[color=blue]
>
> one friend advised me to use "strstr" function[/color]

That's nice. See below (it's still not clear to me which Google sites
are "fixed" and which aren't).



Brian

--
Please quote enough of the previous message for context. To do so from
Google, click "show options" and use the Reply shown in the expanded
header.

[CBFalconer]

Re: need some help

Richard Heathfield wrote:[color=blue]
>[/color]
.... snip ...[color=blue]
>
> 2) the next stage is to write (or find) a function that can read
> an entire line from standard input, reallocating storage as and
> when necessary to ensure that there is sufficient room to store
> the string. For a very simple way to do this that will suit you
> very well, look for Chuck Falconer's ggets() function which,
> last I heard, could be found at:
>
> <http://cbfalconer.home .att.net/download/ggets.zip>
>
> 3) simply call this function in a loop, assigning each pointer
> thus obtained to new[i], where i is your loop counter, running
> from 0 to n-1. What will you do if the function returns NULL, to
> indicate insufficient storage, or perhaps an absence of input data?[/color]

int ggets(char**) returns 0 for success, EOF for eof, and positive
for lack of memory. So a suitable read'em'all loop is:

while (0 == ggets(&buffptr) ) { ... }

--
Some informative links:
news:news.annou nce.newusers

http://www.geocities.com/nnqweb/

http://www.catb.org/~esr/faqs/smart-questions.html

http://www.caliburn.nl/topposting.html

http://www.netmeister.org/news/learn2quote.html

[Richard Heathfield]

Re: need some help

CBFalconer said:
[color=blue]
> Richard Heathfield wrote:[color=green]
>>[/color]
> ... snip ...[color=green]
>>
>> For a very simple way to do this that will suit you
>> very well, look for Chuck Falconer's ggets() function which,
>> last I heard, could be found at:
>>
>> <http://cbfalconer.home .att.net/download/ggets.zip>
>>
>> 3) simply call this function in a loop, assigning each pointer
>> thus obtained to new[i], where i is your loop counter, running
>> from 0 to n-1. What will you do if the function returns NULL, to
>> indicate insufficient storage, or perhaps an absence of input data?[/color]
>
> int ggets(char**) returns 0 for success, EOF for eof, and positive
> for lack of memory. So a suitable read'em'all loop is:
>
> while (0 == ggets(&buffptr) ) { ... }[/color]

Ah, I had forgotten that. Thank you, Chuck.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

[shailesh.budhaner@gmail.com]

Re: need some help

Hi
u can use strstr function which returns int telling position of first
occurance of one string in other string
by using that position(index) u can return poiter.
ash wrote:[color=blue]
> hi friends,
> i have some questions whch is in my last year question papers.i need
> some help to get logic of these questions.
>
> 1) write a C function, that takes two strings as arguments and returns
> a pointer to the first occurrence of 1st string in 2nd string or NULL
> if it is not present.
>
> -- i tried to solve it but it seems that i am not understanding this
> question at all.i am taking this question as:
>
> 1st string- "cat"
> 2nd string-"i like cat."
>
> i have to return pointer that has strarting address of 'c' of cat of
> 2nd string.i can make a program ( that finds a string into another )
> but how to return pointer of that string i don`t know.
> please suggest some advice.
>
> 2) write a 'C' function
> char **readAndcreate (int n)
> the function reads "n" strings from the input and creates a list of
> such strings dynamically using "malloc" library call.
> -- as well as i understand i have to make a linked list that will hold
> the strings(i can make it )but one thing i didn`t understand what this
> function will return, Address of first node of that list or something
> else.if yes please describe how?
>
> my english is not good but i think you have understood my problems.if
> anyone can suggest a good link related to my problems, i will be
> thankful.
> thankx in advance
> :)[/color]

[shailesh.budhaner@gmail.com]

Re: need some help

Hi
u can use strstr function which returns int telling position of first
occurance of one string in other string
by using that position(index) u can return poiter.
ash wrote:[color=blue]
> hi friends,
> i have some questions whch is in my last year question papers.i need
> some help to get logic of these questions.
>
> 1) write a C function, that takes two strings as arguments and returns
> a pointer to the first occurrence of 1st string in 2nd string or NULL
> if it is not present.
>
> -- i tried to solve it but it seems that i am not understanding this
> question at all.i am taking this question as:
>
> 1st string- "cat"
> 2nd string-"i like cat."
>
> i have to return pointer that has strarting address of 'c' of cat of
> 2nd string.i can make a program ( that finds a string into another )
> but how to return pointer of that string i don`t know.
> please suggest some advice.
>
> 2) write a 'C' function
> char **readAndcreate (int n)
> the function reads "n" strings from the input and creates a list of
> such strings dynamically using "malloc" library call.
> -- as well as i understand i have to make a linked list that will hold
> the strings(i can make it )but one thing i didn`t understand what this
> function will return, Address of first node of that list or something
> else.if yes please describe how?
>
> my english is not good but i think you have understood my problems.if
> anyone can suggest a good link related to my problems, i will be
> thankful.
> thankx in advance
> :)[/color]

[Malcolm]

Re: need some help




"ash" <ashishmourya21 @rediffmail.com > wrote[color=blue]
>
> one friend advised me to use "strstr" function, this is a easy way to
> solve that question by use built in function but actually i was trying
> to make this function and i want help in writing that function.
>[/color]
First write the skeleton

/*
mystrstr - find the first occurrence of substring in string
Params: substring - string to search for
string - string to search in.
Returns: pointer to occurence of substring in string, NULL if none found.
*/
char *mystrstr(char *substring, char *string)
{
}

Now for the algorithm.

Step through string until you find a character that matches the first
character of substring.
If you reach the end of the string, return NULL.
Now step through substring comparing every character to the following
characters in string. If you get a mismatch, abort and continue stepping
through string.
If you get to the NUL at the end of substring, you have found a perfect
match. Return the pointer to the start of the substring.

Here's a test funtion.

int main(void)
{
char *sub;

sub = mystrstr("Fred" , "My name is Fred and I am dead");
/* should print out "Fred and I am dead"
printf("%s\n", sub);
sub = mystrstr("Frede rick", "My name is Fred and I am dead"):
/* should print out that sub is null */
printf("%p\n", sub);
sub = mystrstr("Frede rick", "Fred");
/* should print out that sub is null */
printf("%p\n", sub);
sub = mystrstr("Fred" , "Fred, is Fred dead?");
/* should print out "Fred, is Fred dead?" */
printf("%s\n", sub);
sub = mystrstr("Fred" , sub);
/* should print out "Fred dead?");
printf("%s\n", sub);
return 0;
}

--
Buy my book 12 Common Atheist Arguments (refuted)
$1.25 download or $7.20 paper, available www.lulu.com/bgy1mm

[Michael Mair]

Re: need some help

Malcolm schrieb:[color=blue]
> "ash" <ashishmourya21 @rediffmail.com > wrote
>[color=green]
>>one friend advised me to use "strstr" function, this is a easy way to
>>solve that question by use built in function but actually i was trying
>>to make this function and i want help in writing that function.
>>[/color]
>
> First write the skeleton
>
> /*
> mystrstr - find the first occurrence of substring in string
> Params: substring - string to search for
> string - string to search in.
> Returns: pointer to occurence of substring in string, NULL if none found.
> */
> char *mystrstr(char *substring, char *string)
> {
> }
>
> Now for the algorithm.
>
> Step through string until you find a character that matches the first
> character of substring.
> If you reach the end of the string, return NULL.
> Now step through substring comparing every character to the following
> characters in string. If you get a mismatch, abort and continue stepping
> through string.
> If you get to the NUL at the end of substring, you have found a perfect
> match. Return the pointer to the start of the substring.
>
> Here's a test funtion.
>
> int main(void)
> {
> char *sub;
>
> sub = mystrstr("Fred" , "My name is Fred and I am dead");
> /* should print out "Fred and I am dead"[/color]

ITYM
/* should print out "Fred and I am dead" */
[color=blue]
> printf("%s\n", sub);[/color]

No prototype in scope. #include <stdio.h>
[color=blue]
> sub = mystrstr("Frede rick", "My name is Fred and I am dead"):[/color]
^
;
[color=blue]
> /* should print out that sub is null */
> printf("%p\n", sub);
> sub = mystrstr("Frede rick", "Fred");
> /* should print out that sub is null */
> printf("%p\n", sub);
> sub = mystrstr("Fred" , "Fred, is Fred dead?");
> /* should print out "Fred, is Fred dead?" */
> printf("%s\n", sub);
> sub = mystrstr("Fred" , sub);[/color]

ITYM:
sub = mystrstr("Fred" , sub+1);
This is the thing I originally wanted to remark but I
foundthe other stuff along the way...
[color=blue]
> /* should print out "Fred dead?");[/color]

Once again: Missing */ -- in this case an error.
[color=blue]
> printf("%s\n", sub);
> return 0;
> }[/color]

Cheers
Michael
--
E-Mail: Mine is an /at/ gmx /dot/ de address.

[osmium]

Re: need some help

"ash" writes:
[color=blue]
> one friend advised me to use "strstr" function, this is a easy way to
> solve that question by use built in function but actually i was trying
> to make this function and i want help in writing that function.[/color]

Your friend is what we in America call a "smartass". It is not always a good
idea to try to show the instructor that you are more clever than he is.

You "friends" proposal answers the question: "Write a function that calls a
function that takes two strings and .....".
That is not what you were told to do.