指定文字列に挟まれた文字列を取得する

function str_extraction ($str_old, $str_from, $str_to, $plus_flag=False){

	$int_from = strpos($str_old, $str_from);

	if ($int_from === False) {

		return False;

	} else {

		$int_from = $int_from + strlen($str_from);

	}

	$int_to = strpos($str_old, $str_to, $int_from);

	if ($int_to === False) {

		return False;

	}
	$str_new = '';

	if ($plus_flag) {

		$str_new .= $str_from;

	}

	$str_new .= substr($str_old, $int_from, $int_to - $int_from);

	if ($plus_flag) {

		$str_new .= $str_to;

	}
	return $str_new;

}