An implementation of strtok

strtok.c

#include <stddef.h>
#include <stdbool.h>
#include <stdio.h>

bool is_delim(char c, char *delim)
{
  while(*delim != '\0')
  {
    if(c == *delim)
      return true;
    delim++;
  }
  return false;
}

char *strtok1(char *s, char *delim)
{
  static char *p; // start of the next search 
  if(!s)
  {
    s = p;
  }
  if(!s)
  {
    // user is bad user 
    return NULL;
  }

  // handle beginning of the string containing delims
  while(1)
  {
    if(is_delim(*s, delim))
    {
      s++;
      continue;
    }
    if(*s == '\0')
    {
      return NULL; // we've reached the end of the string
    }
    // now, we've hit a regular character. Let's exit the
    // loop, and we'd need to give the caller a string
    // that starts here.
    break;
  }

  char *ret = s;
  while(1)
  {
    if(*s == '\0')
    {
      p = s; // next exec will return NULL
      return ret;
    }
    if(is_delim(*s, delim))
    {
      *s = '\0';
      p = s + 1;
      return ret;
    }
    s++;
  }
}

int main()
{
  // char s[] = "     'hi;;;there;';how'are you'''";
  char s[] = "'''hi there";
  char *delim = "; '";
  char *p = strtok1(s, delim);
  while(p)
  {
    printf("%s\n", p);
    p = strtok1(NULL, delim);
  }
}