note for "strtok"

description
  sequence calls to this function split str into tokens
  tokens are sequences of contiguous characters separated by any of characters that are part of delimiters
how to call
  first call, str = C string, start positon = first character of "C string"
  subsequent call, str = NULL, start position = position after the end of the last token
  if terminating null character of str is found, all subsequent calls return a null pointer
position of token
  starting position = first character not contained in delimiter, from starting location
  ending position = first character contained in delimiter.
  end of the token = null-character
  beginning of the token is returned by the function
others
  the point of position of last token is kept internally
parameters
  str
    c string
    "str" is modified
    if str == null, this function continues scanning, start position = previous successful call end position
  delimiters
    c string
    contains delimiter characters
    these characters can be different from one call to another
return value
  a pointer to the beginning of the token, if a token is found
  null, otherwise