#define _GNU_SOURCE
#include <string.h>

char* strsep(char** str, const char* sep) {
  char *s = *str, *end;
  if (!s)
    return NULL;
  end = s + strcspn(s, sep);
  if (*end)
    *end++ = 0;
  else
    end = 0;
  *str = end;
  return s;
}