strtok function in c ..help

[abdullah]

hi,

i am experimenting with the strtok function in c and when i compile my code i dont get any error ..but when i try to run it , i get a segmentation fault. can anyone please point me in the right direction? thanks

the code i am trying to run is:


#include <stdio.h>
#include <stdlib.h>

int main ()
{
char * haystack = "hi how are you";
char * token;

token = strtok(haystack, '/');
while (token != NULL) {
printf("The token is: %s \n", token);
printf("The haystack is: %s \n",haystack);
token = strtok(haystack, '/');
}

return 0;
}

[ibrahim34]

Assalam Aleykoum



char * haystack = "hi how are you";
char * token;
token = strtok(haystack, '/');



First , there is a memory allocation problem with this because generaly when you make char * ="something" you create a pointer to a read only memory ( depending of the OS ..) , maybe const char * ="your_string" can solve the problem.


or you can declare haystack on the stack like this and it will works :



char haystack[] = "This code works.";
char * token;
token = strtok(haystack, " ");



And then ( second problem ) :


After a first call to strtok, the function may be called with NULL as string parameter, and it will follow by where the last call to strtok found a delimiter.
delimiters may vary from a call to another.

http://www.cplusplus.com/ref/cstring/strtok.html



finally these two code works fine


1 ) static allocation of haystack



int main()
{

char haystack[] = "This code works.";
char * token;

token = strtok(haystack, " ");
while (token != NULL) {
printf("The token is: %s \n", token);
token = strtok(NULL, " ");
}

return 0;
}



2 ) dynamic allocation of haystack




int main( )
{
char string[] = "This code works";
char *haystack = NULL;
char * token = NULL;
haystack = (char*) malloc (sizeof(string));
strcpy(haystack,string);
token = strtok(haystack, " ");
while (token != NULL) {
printf("The token is: %s \n", token);
token = strtok(NULL, " ");
}

return 0;
}




Wa Salam

[furqan]

Looks like my C needs brushin up lol... Good work...

[abdullah]

thanks for the reply bro.. i just saw it

[ibrahim34]

Salams

you may find that usefull too :

http://www.sgi.com/tech/stl/basic_string.html

It is the STL string class and it is a very powerful class to handle and manipulate sequence of characters in C++

[awara]

salaam guys,
juzz a small contribution.
haystack = (char*) malloc (sizeof(string));
could be
haystack = (char*) malloc (sizeof(string)+1);

when copying a string which is done in the next step, always add one for the null terminated string :), or heap cries in the long run.

and juzz a free(haystack) before return 0.

Holy God, did i get into troubles cuz of these mem. allocation things. haunts me now, newayz, cheer up.
salaam alaikum.


Assalam Aleykoum


2 ) dynamic allocation of haystack




int main( )
{
char string[] = "This code works";
char *haystack = NULL;
char * token = NULL;
haystack = (char*) malloc (sizeof(string));
strcpy(haystack,string);
token = strtok(haystack, " ");
while (token != NULL) {
printf("The token is: %s \n", token);
token = strtok(NULL, " ");
}

return 0;
}




Wa Salam