Handle malformed FEN

The code happily accepts /9/. It doesn't check that the rank spells out exactly 8 files. It doesn't check that the input spells out exactly 8 ranks. In both cases, hello buffer overflow.

It also doesn't check that the piece letter makes sense (may be good for the fairy chess. but still ...).

fen.substr(iter + 1, 3); looks strange, as it has no effect. Along the same line, I don't see en passant handling.

The code assumes that there is exacly one space between board and turn, and between turn and castling rights. I am not sure that FEN standard mandates it. If it does not, allow multiple spaces; if it does, prepare to handle a malformed one.

More functions please, aka no naked loops

Every time you feel compelled to annotate a loop with a comment like

  // parse the board first

consider to factor the loop out into a function with the proper name. Something along the lines of

  void Chess::parse_fen (const std::string& fen)
  {
      std::string::iterator it = fen.begin();
      it = parse_board(it);
      it = parse_turn(it);
      it = parse_castle_rights(it);
      ....
  }

Handle malformed FEN

The code happily accepts /9/. It doesn't check that the rank spells out exactly 8 files. It doesn't check that the input spells out exactly 8 ranks. In both cases, hello buffer overflow.

It also doesn't check that the piece letter makes sense (may be good for the fairy chess. but still ...).

fen.substr(iter + 1, 3); looks strange, as it has no effect. Along the same line, I don't see en passant handling.

The code assumes that there is exacly one space between board and turn, and between turn and castling rights. I am not sure that FEN standard mandates it. If it does not, allow multiple spaces; if it does, prepare to handle a malformed one.

More functions please, aka no naked loops

Every time you feel compelled to annotate a loop with a comment like

  // parse the board first

consider to factor the loop out into a function with the proper name. Something along the lines of

  void Chess::parse_fen (const std::string& fen)
  {
      std::string::iterator it = fen.begin();
      it = parse_board(it);
      it = parse_turn(it);
      it = parse_castle_rights(it);
      ....
  }