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strtok problem

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

Mar 29 '06 #1
5 7251
pl**********@gmail.com 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

Mar 29 '06 #2
pl**********@gmail.com 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.
Mar 29 '06 #3
Puppet_Sock wrote:
pl**********@gmail.com 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
Mar 29 '06 #4
In article <11**********************@g10g2000cwb.googlegroups .com>,
pl**********@gmail.com 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.
Mar 30 '06 #5
In article
<11**********************@g10g2000cwb.googlegroups .com>,
pl**********@gmail.com 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.

Mar 30 '06 #6

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