运行时有时会出现验证码，有时不出现，请教是怎么回事

Question

<?phprequire_once'string.func.php';//通过gd库做验证码//创建画布$width=80;$height=28;$image=imagecreatetruecolor($width,$height);$white=imagecolorallocate($image,255,255,255);$black=imagecolorallocate($image,0,0,0);//用填充矩形填充画布imagefilledrectangle($image,1,1,$width-2,$height-2,$white);$type=1;$length=4;$chars=buildrandomstring($type,$length);$sess_name="verify";$_SESSION[$sess_name]=$chars;$fontfiles=array("msyh,ttc","msyhb.ttc","msyhl.ttc","simkai.ttf","simsun.ttc","simyou.ttf","stzhongs.ttf");for($i=0;$i<$length;$i++){ $size=mt_rand(14,18); $angle=mt_rand(-15,15); $x=5+$i*$size; $y=mt_rand(20,26); $fontfile="../fonts/".$fontfiles[mt_rand(0,count($fontfiles)-1)]; $color=imagecolorallocate($image,mt_rand(50,90),mt_rand(80,200),mt_rand(90,180)); $text=substr($chars,$i,1); imagettftext($image,$size,$angle,$x,$y,$color,$fontfile,$text);}header("content-type:image/gif");imagegif($image);imagedestroy($image);

Answer 1

imagettftext($image,$size,$angle,$x,$y,$color,$fontfile,$text);

不出验证码时提示这一行错误，“imagettftext(): Invalid font filename in <b>F:\eweb\lib\image.func.php</b> on line <b>29</b><br />