[C] strtok / used in Kernel, this 'reinventing wheel'

#include <stdio.h>
#include <string.h>


char* sp = NULL; /* the start position of the string */

char* strtok1(char* str, const char* delimiters) {

    int i = 0;
    int len = strlen(delimiters);

    /* check in the delimiters */
    if(len == 0)
        printf("delimiters are empty\n");

    /* if the original string has nothing left */
    if(!str && !sp)
        return NULL;

    /* initialize the sp during the first call */
    if(str && !sp)
        sp = str;

    /* find the start of the substring, skip delimiters */
    char* p_start = sp;
    while(1) {
        for(i = 0; i < len; i ++) {
            if(*p_start == delimiters[i]) {
                p_start ++;
                break;
            }
        }

        if(i == len) {
               sp = p_start;
               break;
        }
    }

    /* return NULL if nothing left */
    if(*sp == '\0') {
        sp = NULL;
        return sp;
    }

    /* find the end of the substring, and
        replace the delimiter with null */
    while(*sp != '\0') {
        for(i = 0; i < len; i ++) {
            if(*sp == delimiters[i]) {
                *sp = '\0';
                break;
            }
        }

        sp ++;
        if (i < len)
            break;
    }

    return p_start;
}

/* https://fengl.org/2013/01/01/implement-strtok-in-c-2/ */
/* // ULtra-simple. haha! */
/* // ------------------------------------------- */
/* char* strtok1(char *str, const char* delim) { */
/*   static char* _buffer; */
/*   if(str != NULL) _buffer = str; */
/*   if(_buffer[0] == '\0') return NULL; */

/*   char *ret = _buffer, *b; */
/*   const char *d; */

/*   for(b = _buffer; *b !='\0'; b++) { */
/*     for(d = delim; *d != '\0'; d++) { */
/*       if(*b == *d) { */
/*         *b = '\0'; */
/*         _buffer = b+1; */

/*         // skip the beginning delimiters */
/*         if(b == ret) { */
/*           ret++; */
/*           continue; */
/*         } */
/*         return ret; */
/*       } */
/*     } */
/*   } */

/*   return ret; */
/* } */


int main ()
{
  char str[] ="- This, a sample string.";
  char * pch;
  printf ("Splitting string \"%s\" into tokens:\n",str);
  pch = strtok1(str," ,.-");
  while (pch != NULL)
    {
      printf ("%s\n",pch);
      pch = strtok1(NULL, " ,.-");
    }
  return 0;
}