problem with the last string token divided by strtok.

[mattmao]

Here is my code, just to test the strtok functionality:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct sampleClass
{
   int num;
   char *text;
   struct sampleClass *next;
};
 
typedef struct sampleClass node;
 
void fillinnode(node *target, int num, char **text);
void printoutnodes(node *startnode);
 
 
int main()
{
   char text[30];
   char *token1, *token2, *token3;
   int i;
 
   node *a=(node *) malloc(sizeof(node));
   node *b=(node *) malloc(sizeof(node));
   node *c=(node *) malloc(sizeof(node));
 
   a->next = b;
   b->next = c;
   c->next = NULL;
 
   for(i=0; i<30; i++)
   {
      if (i%10 == 0&&i!=0)
         text[i]=':';
      else text[i]='*';
   }
 
   printf("original string is");
   for(i=0; i<30; i++)
      printf("%c", text[i]);
   printf("\n");
 
   token1 = strtok(text, ":");
   printf("token1=%s\n", token1);
 
   token2 = strtok(NULL, ":");
   printf("token2=%s\n", token2);
 
   token3 = strtok(NULL, "");
   printf("token3=%s\n", token3);
 
   fillinnode(a, 1, &token1);
   fillinnode(b, 2, &token2);
   fillinnode(c, 3, &token3);
 
   printoutnodes(a);
}
 
void fillinnode(node *target, int num, char **text)
{
   target->num = num;
   target->text = *text;
}
 
void printoutnodes(node *startnode)
{
   node *temp = startnode;
   while(temp!= NULL)
   {
      printf("%d", temp->num);
      printf("%s", temp->text);
      temp = temp->next;
   }
}

It compiled well with gcc and runs. However, the last string token is not closed well, see the output:

charlie$ gcc why.c
charlie$ ./a.out
original string is**********:*********:*********
token1=**********
token2=*********
token3=*********
1**********2*********3*********��charlie$
 

In my linux terminal, the end of token is displayed with a '(?)' symbol, which probably means this token is not closed well. How to fix this problem?

[weaknessforcats]

Problem 1: Your text string has no null terminator. strtok uses that to tell where your string ends:

for(i=0; i<30; i++)
{
if (i%10 == 0&&i!=0)
text[i]=':';
else text[i]='*';
}
text[i] = '\0'; <<<< I added this.

Problem 2: your text array ends up with 33 characters in it and you allocated only 30. This causes a crash when main() returns. I changed text to an array of 40 and the crash went away.

Clearly, it's time for you to start learning how to use your debugger.

[mattmao]

Thanks a lot. I've decided rewrite my code to fix this problem. The null terminator is really a big issue to think about...