Iterating through a string and separating input by spaces in C

I have a string such as "first second" and my desired result is for this output:

first 
second

But the output I am getting is:

first
first second

I know there is a problem either in my update statements or when I create a substring. If anybody could help me out that would be great. Here is my code down below:

int counter = 0; //counter used in loop
int index = test->current_index; //holds the current index of my string, it's initially 0
char *string = test->myString; //holds the whole string

char token_buffer = string[index];

   //before loop: index = 0, counter = 0

   while(test->current_index <= test->end_index) //test->end_index holds last index of string

    {
       while(token_buffer != ' ')
       {
         counter++;
         token_buffer = string[index + counter];

       }    

    char *output_token = malloc(counter+1);


   strncpy( output_token, string, counter );

  //printing token
  printf("%s \n", output_token);


 //update loop (possible problem area!)
  test->current_index += counter;
  index += counter;
  token_buffer+=string[counter];
  counter =0;
  }

return 0;
}