Parse error: syntax error, unexpected 'function' (T_FUNCTION), expecting ',' or ';'错误提示怎么解释？？

错误提示：：Parse error: syntax error, unexpected 'function' (T_FUNCTION), expecting ',' or ';in D:\php\php\vcode.class.php on line 标记行（*）！！！！！
部分源代码：：
class Vcode{
private $width;//验证码的宽与高
***function __construct($width=80,$height=20,$codeNum=4){
$this->width =$width;
$this->height =$height;
$this->codeNum =$codeNum;
$number = floor($height*$width/15);
if($number >240-$codeNum){
$this->disturbColorNum = 240-$codeNum;
else
$this->disturbColorNum = $number;
}
$this->checkCode = $this->createCheckCode();

}