PHP generates verification code image does not display problem_PHP tutorial

When I was doing a PHP verification code program today, I found that the generated image was not displayed. I thought it was because the PHP gd library was not opened. I checked with phpinfo and found that it can be opened. The editor below will introduce to you how to solve this problem. way.

After clearing the BOM, the code is also written starting from the top line, and the gd library is also enabled. Judging from this, it is probably not a problem with the gd library, but may be in the code of the program.

Code to generate verification code:

The code is as follows

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/* * Verification code generation program */ $letter = ''; //Get random numbers for ($i=0; $i<2; $i++) { $letter .= chr(mt_rand(48,57)); } //Get random letters for ($i=0; $i<2; $i++) { $letter .= chr(mt_rand(65,90)); } //Reconstruct character order $strs = str_split($letter); shuffle ($strs); $rndstring = ""; while (list ( , $str) = each ($strs)) { $rndstring .= $str; } //If GD is supported, draw if(function_exists("imagecreate")) { //Write cookie to browser setcookie("zjs_ckstr", md5( strtolower($rndstring) ), time()+300,'/');//Verification code is valid for 5 minutes $rndcodelen = strlen($rndstring); //Image size $im = imagecreate(100,30); //$im = imagecreatefromgif("code.gif"); //Font $font_type = dirname(dirname(__FILE__))."/data/font/AvantGardeBookBT.ttf"; //Background color $backcolor = imagecolorallocate($im,255,255,255); //Font color //Does not support imagettftext $fontColor = ImageColorAllocate($im, 0,0,0); //Support imagettftext $fontColor2 = ImageColorAllocate($im, 0,0,0); //Shadow $fontColor1 = ImageColorAllocate($im, 255,255,25); //Add background noise $pixColor = imagecolorallocate($im, 199, 199, 199);//Noise color for($j=0; $j<1000; $j++){ imagesetpixel($im, rand(0,100), rand(0,30), $pixColor); } //Add background line for($j=0; $j<=3; $j++){ //Background line color           $lineColor1 = ImageColorAllocate($im, rand(0, 255),rand(0, 255),rand(0, 255)); //Background line direction size Imageline($im,rand(0,40),rand(3,25),rand(40,88),rand(3,25),$lineColor1); }   $strposs = array(); //Text for($i=0;$i<$rndcodelen;$i++){ If(function_exists("imagettftext")){              $strposs[$i][0] = $i*16+17;//x-axis               $strposs[$i][1] = mt_rand(20,23);//y-axis Imagettftext($im, 5, 5, $strposs[$i][0]+1, $strposs[$i][1]+1, $fontColor1, $font_type, $rndstring[$i]); } else{ Imagestring($im, 5, $i*16+7, mt_rand(2, 4), $rndstring[$i], $fontColor); } } //Text for($i=0;$i<$rndcodelen;$i++){ If(function_exists("imagettftext")){ Imagettftext($im, 16,5, $strposs[$i][0]-1, $strposs[$i][1]-1, $fontColor2, $font_type, $rndstring[$i]); } } header("Pragma:no-cachern"); header("Cache-Control:no-cachern"); header("Expires:0rn"); //Output a specific type of image format, the priority is gif -> jpg if(function_exists("imagegif")){ header("content-type:image/gifrn"); Imagegif($im); }else{ header("content-type:image/jpegrn"); Imagejpeg($im); } ImageDestroy($im); } ?>

I felt like there was no problem anymore. Later, I found a senior person in Baidu who said that the key is to add ob_clean. This made me think about the reason.

Solution

ob_clean(); //Key code to prevent the problem of 'the image cannot be displayed because of its own errors'.

Add to header before output

The code is as follows

代码如下	复制代码
header('Content-Type: image/png');

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header('Content-Type: image/png');

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TechArticleWhen I was doing a php verification code program today, I found that the generated image was not displayed. I initially thought it was because the php gd library was not working. Open it. If you check it with phpinfo, it can be opened. Let me introduce it to you...