Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Programming > C++ > strtok problem

Reply
Thread Tools

strtok problem

 
 
plmanikandan@gmail.com
Guest
Posts: n/a
 
      03-29-2006
Hi,
I need to split the value stored in a string and store them to another
charrecter array.I am using strtok function.But i am getting invalid
output when there is no value between delimiter

my code
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
void main()
{

char *pch;
char *parameters[4];
int paramcount=0;

char b[]="mani,raju,musa,kumar";

pch=strtok(b,",");
while (pch != NULL)
{
//parameters[paramcount]=pch;
parameters[paramcount]=(char*)malloc(strlen(pch) + 1);
strcpy(parameters[paramcount],pch);
paramcount++;
pch = strtok (NULL, ",");
}//while (pch != NULL)

for(int t=0;t<4;t++)
printf("\n%s\n",parameters[t]);

}
the above code works fine.when i change the input as follows
char b[]="mani,,,kumar"
The output is not correct.
How to free the memory allocated?
how to handle strtok when there is no value between delimiter

Regards,
Manikandan

 
Reply With Quote
 
 
 
 
Puppet_Sock
Guest
Posts: n/a
 
      03-29-2006
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:
[snip]
> pch=strtok(b,",");

[snip]
> the above code works fine.when i change the input as follows
> char b[]="mani,,,kumar"
> The output is not correct.
> How to free the memory allocated?
> how to handle strtok when there is no value between delimiter


I am convinced that the main purpose of the strtok function being
in the library is to catch new coders in the knees.

Carefully read up on the strtok function in your compiler's docs.
Note what happens when there are multiple delimeters with
nothing between them. So, your "not working" input will be
equivalent to

char b[]="mani,kumar"

that is, there's no way for you to use strtok to get those missing
fields in the middle.

Also, read up in your docs about the various warnings and caveats
about using strtok. The security warning that should be there, for
example. And the warning about a static variable being used so that
multiple overlapping calls with different strings to tokenize will
interfere with eachother.

My opinion: Don't use strtok. Roll up your own parsing class,
preferably using std::string instead of char arrays. But even if
you can't use std::string, drop the use of strtok.

Write yourself a class that takes your input, copies it to an
internal buffer, then parses it out to a vector of tokens. Give
it the behaviour you need it to have with regard to missing
entries. Make sure you follow all the "motherhood" rules
about class design such as the rule of 3, and so on. Then
give it a small number of "get" funcs that pull out the number
of items in the vector, and the "nth" item in the list. You
can then have a really good time deciding what to do about
such things as asking for an element past the end (the
7th element when there are only 4, as an example.)

You can even have such things as multiple delimeters,
delims that are more than one char, even calculated delims
that depend on rules such as a space after a period is a
delim, but a space after anything else is not.
Socks

 
Reply With Quote
 
 
 
 
Pete Becker
Guest
Posts: n/a
 
      03-29-2006
(E-Mail Removed) wrote:

> the above code works fine.when i change the input as follows
> char b[]="mani,,,kumar"
> The output is not correct.


Well, that depends on what "correct" means. According to the definition
of strotk, the new input has two data fields, separated by three commas.
strtok swallows all consecutive occurrences of characters in the
delimiter string.

> How to free the memory allocated?


Same way you allocated it: step through the array and call delete[] on
each allocated block.

> how to handle strtok when there is no value between delimiter
>


strtok doesn't do that. You can use strcspn if you don't mind doing a
little more bookkeeping. Or you can use the STL algorithm find_first_of
to find the next occurrence of the delimiter in a C string. Or, at the
cost of a little more overhead, copy the text into a C++ string object,
and use its member function find_first_of.

--

Pete Becker
Roundhouse Consulting, Ltd.
 
Reply With Quote
 
Sgt. York
Guest
Posts: n/a
 
      03-29-2006
Puppet_Sock wrote:
> (E-Mail Removed) wrote:
> [snip]
>> pch=strtok(b,",");

> [snip]
>> the above code works fine.when i change the input as follows
>> char b[]="mani,,,kumar"
>> The output is not correct.
>> How to free the memory allocated?
>> how to handle strtok when there is no value between delimiter

>
> I am convinced that the main purpose of the strtok function being
> in the library is to catch new coders in the knees.
>
> Carefully read up on the strtok function in your compiler's docs.
> Note what happens when there are multiple delimeters with
> nothing between them. So, your "not working" input will be
> equivalent to
>
> char b[]="mani,kumar"
>
> that is, there's no way for you to use strtok to get those missing
> fields in the middle.
>
> Also, read up in your docs about the various warnings and caveats
> about using strtok. The security warning that should be there, for
> example. And the warning about a static variable being used so that
> multiple overlapping calls with different strings to tokenize will
> interfere with eachother.
>
> My opinion: Don't use strtok. Roll up your own parsing class,
> preferably using std::string instead of char arrays. But even if
> you can't use std::string, drop the use of strtok.
>
> Write yourself a class that takes your input, copies it to an
> internal buffer, then parses it out to a vector of tokens. Give
> it the behaviour you need it to have with regard to missing
> entries. Make sure you follow all the "motherhood" rules
> about class design such as the rule of 3, and so on. Then
> give it a small number of "get" funcs that pull out the number
> of items in the vector, and the "nth" item in the list. You
> can then have a really good time deciding what to do about
> such things as asking for an element past the end (the
> 7th element when there are only 4, as an example.)
>
> You can even have such things as multiple delimeters,
> delims that are more than one char, even calculated delims
> that depend on rules such as a space after a period is a
> delim, but a space after anything else is not.
> Socks
>


Better yet, use John Bandela's Boost tokenizer (www.boost.org). From
there, you'll likely discover other boost delicacies that will make the
library almost indispensable.

-York
 
Reply With Quote
 
Daniel T.
Guest
Posts: n/a
 
      03-30-2006
In article <(E-Mail Removed) .com>,
(E-Mail Removed) wrote:

> Hi,
> I need to split the value stored in a string and store them to another
> charrecter array.I am using strtok function.But i am getting invalid
> output when there is no value between delimiter
>
> my code
> #include<stdio.h>
> #include<string.h>
> #include<stdlib.h>
> void main()
> {
>
> char *pch;
> char *parameters[4];
> int paramcount=0;
>
> char b[]="mani,raju,musa,kumar";
>
> pch=strtok(b,",");
> while (pch != NULL)
> {
> //parameters[paramcount]=pch;
> parameters[paramcount]=(char*)malloc(strlen(pch) + 1);
> strcpy(parameters[paramcount],pch);
> paramcount++;
> pch = strtok (NULL, ",");
> }//while (pch != NULL)
>
> for(int t=0;t<4;t++)
> printf("\n%s\n",parameters[t]);
>
> }
> the above code works fine.when i change the input as follows
> char b[]="mani,,,kumar"
> The output is not correct.
> How to free the memory allocated?
> how to handle strtok when there is no value between delimiter


I'm thinking your confused as accidentally posted this in a C++
newsgroup instead of a C newsgroup. Could that be the case? If not...

I suggest you use some standard C++ components:

#include <algorithm> // for copy & find
#include <iostream> // for cout
#include <iterator> // for ostream_iterator
#include <string>
#include <vector>

using namespace std;

int main()
{
//char b[]="mani,raju,musa,kumar";
char b[]="mani,,,kumar";

vector<string> vec;
const char* first = b;
const char* last = b + strlen( b );
while ( first != last ) {
const char* next = find( first, last, ',' );
vec.push_back( string( first, next - first ) );
first = min( next + 1, last );
}
copy( vec.begin(), vec.end(),
ostream_iterator<string>( cout, "\n" ) );
}


--
Magic depends on tradition and belief. It does not welcome observation,
nor does it profit by experiment. On the other hand, science is based
on experience; it is open to correction by observation and experiment.
 
Reply With Quote
 
Daniel T.
Guest
Posts: n/a
 
      03-30-2006
In articl
<(E-Mail Removed) .com>
(E-Mail Removed) wrote

> Hi
> I need to split the value stored in a string and store them t

anothe
> charrecter array.I am using strtok function.But i am getting invali
> output when there is no value between delimite
>
> my cod
> #include<stdio.
> #include<string.
> #include<stdlib.
> void main(
>
>
> char *pch
> char *parameters[4]
> int paramcount=0
>
> char b[]="mani,raju,musa,kumar"
>
> pch=strtok(b,",")
> while (pch != NULL
>
> //parameters[paramcount]=pch
> parameters[paramcount]=(char*)malloc(strlen(pch) + 1)
> strcpy(parameters[paramcount],pch)
> paramcount++
> pch = strtok (NULL, ",")
> }//while (pch != NULL
>
> for(int t=0;t<4;t++
> printf("\n%s\n",parameters[t])
>
>
> the above code works fine.when i change the input as follow
> char b[]="mani,,,kumar
> The output is not correct
> How to free the memory allocated
> how to handle strtok when there is no value between delimite
>

I'm thinking your confused as accidentally posted this in a C++
newsgroup instead of a C newsgroup. Could that be the case? If not..

I suggest you use some standard C++ components

#include <algorithm> // for copy & fin
#include <iostream> // for cou
#include <iterator> // for ostream_iterato
#include <string
#include <vector

using namespace std

int main(

//char b[]="mani,raju,musa,kumar"
char b[]="mani,,,kumar"

vector<string> vec
const char* first = b
const char* last = b + strlen( b )
while ( first != last )
const char* next = find( first, last, ',' )
vec.push_back( string( first, next - first ) )
first = min( next + 1, last )

copy( vec.begin(), vec.end()
ostream_iterator<string>( cout
"\n" ) )


--
Magic depends on tradition and belief. It does not welcom
observation
nor does it profit by experiment. On the other hand, science is base
on experience; it is open to correction by observation and experiment

 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
strtok() problem ern C Programming 12 09-22-2005 10:52 PM
crazy problem with strtok puttings ptrs in **argv alef@xs4all.nl C Programming 3 07-27-2005 04:37 AM
strtok problem - strcmp collinm C Programming 4 03-24-2005 09:50 PM
strtok problem Ram Laxman C Programming 3 05-03-2004 03:17 PM
strtok problem jorntk@yahoo.com C Programming 4 08-29-2003 11:26 AM



Advertisments