Strtok:I dont know why this program keeps failing - c

Question

In this program the char *token is initialized with a weird garbage value.I am unable to sort it out. Here's the source code:
#include<iostream>
#include<string.h>
#include<stdlib.h>
void fetch_value(char *string,int pos,char *dest)
{
    char *token;
    int i=0;
    token=strtok(string,",");
    if(pos>1)
    {
        token=strtok(NULL,",");
        while(i<pos-1){
            token=strtok(NULL,",");
            printf("token =%s\n",token);
            i++;
        }
        strcpy(dest,token);
    }
    else
    {
        strcpy(dest,token);
    }
}
int main(void)
{
    char checking[100];
    memset(checking,0x00,sizeof(checking));
    fetch_value("14174000100,35679700322,35679700322,35679700322,
            35679700322,14174000999,919440710210000,1",0,checking);
    printf("checking=%s\n",checking);
    return 0;
}
Your help, feedback or suggestions is greatly appreciated.

Answer 1

The first argument of strtok must be modifiable. Your code passes a string literal, which is not modifiable. This leads to undefined behavior.
The simplest modification that will fix the problem is as follows:
char numList[] = "14174000100,35679700322,35679700322,35679700322,35679700322,14174000999,919440710210000,1";
fetch_value(numList, 0, checking);
You should also note that strtok is an older function which is not reentrant, because it uses static variables to save its state. In the new code you should use the reentrant version of the function - strtok_r, which requires you to pass memory for saving the state.

Answer 2

Do this instead:
int main(void)
{
char checking[100];
memset(checking,0x00,sizeof(checking));
char string[] = "14174000100,35679700322,35679700322,35679700322,
35679700322,14174000999,919440710210000,1";
//now string can be modified.
fetch_value(&string[0],0,checking);
printf("checking=%s\n",checking);
return 0;
}