What should I do if the php verification code cannot be generated in the background?

Solution to the problem that the PHP verification code cannot be generated in the background: 1. Add the "header('Content-type: image/png')" statement; 2. Clear the output cache through "ob_clean();".

The operating environment of this article: windows7 system, PHP7.1 version, DELL G3 computer

What should I do if the php verification code background cannot be generated? ?

PHP verification code cannot generate images, the reason is solved:

When generating images, header('Content-type: image/png'); cannot have output in front! ! !

Or, add: ob_clean(); Even if you use output, you can clear the output cache through this sentence! Very important! ! !

Of course, you must first open the gd2 library, which can be viewed through phpinfo. After clearing the BOM, the code is also written starting from the top line, so the problem may occur in the code. After some research, I found that I still need to change the program and add the ob_clean() statement in front of the header, so that it can run! Haha, coding and debugging programs is like being a doctor, and you will become strong with practice.

<?php
//设置 验证码高度宽度\上面字符个数
$img_w = 70;
$img_h = 22;
$font = 5;
$char_len = 5;
//数组合并， range()函数返回一个范围数组
$char = array_merge ( range ( &#39;a&#39;, &#39;z&#39; ), range ( &#39;A&#39;, &#39;Z&#39; ), range ( &#39;1&#39;, &#39;9&#39; ) );
$rand_keys = array_rand ( $char, $char_len ); //随机从数组中取指定个数的元素,生成键值
if ($char_len == 1) { //若只有一个数，则array_rand()返回非数组类型
         $rand_keys = array ($rand_keys );
}
shuffle($rand_keys);  //可以不用
$code = &#39;&#39;;
foreach ( $rand_keys as $k ) {
         $code .= $char [$k];
}
session_start ();
$_SESSION [&#39;captcha&#39;] = $code;
 
//添加线、色
//创建新图像
$img = imagecreatetruecolor ( $img_w, $img_h );
//分配颜色
$bg_color = imagecolorallocate ( $img, 0xcc, 0xcc, 0xcc );
//画布背景色
imagefill ( $img, 0, 0, $bg_color );
//干扰线
for($i = 0; $i < 300; ++$i) {
         $color = imagecolorallocate ( $img, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) );
         imagesetpixel ( $img, mt_rand ( 0, $img_w ), mt_rand ( 0, $img_h ), $color );
}
for($i = 0; $i <= 10; ++ $i) {
         //设置直线颜色
         $color = imageColorAllocate ( $img, mt_rand ( 0, 255 ), mt_rand ( 0, 255 ), mt_rand ( 0, 255 ) );
         //在$img图像上随机画一条直线
         imageline ( $img, mt_rand ( 0, $img_w ), mt_rand ( 0, $img_h ), mt_rand ( 0, $img_w ), mt_rand ( 0, $img_h ), $color );
         //imagesetpixel($img,mt_rand(0,$img_w),mt_rand(0,$img_h),$color);
}
 
//加加框
$rect_color = imagecolorallocate ( $img, 0x90, 0x90, 0x90 );
imagerectangle ( $img, 0, 0, $img_w - 1, $img_h - 1, $rect_color );
$str_color = imagecolorallocate ( $img, mt_rand ( 0, 100 ), mt_rand ( 0, 100 ), mt_rand ( 0, 100 ) );
$font_w = imagefontwidth ( $font );
$font_h = imagefontheight ( $font );
$str_len = $font_w * $char_len;
imagestring ( $img, $font, ($img_w - $str_len) / 2, ($img_h - $font_h) / 2, $code, $str_color );

Set string color

$str_color = imageColorAllocate($img, mt_rand(0, 100), mt_rand(0, 100),mt_rand(0, 100));
//设定字符串位置
$font_w = imageFontWidth($font);  //字体宽
$font_h = imageFontHeight($font); //字体高
$str_w = $font_w * $char_len;     //字符串宽
imageString($img, $font, ($img_w-$str_w)/2, ($img_h-$font_h)/2, $code, $str_color);
echo 'ddd'; //输出影响生成图片，查找了大半天的原因终于找到了
ob_clean(); //也可以加上这句，这样前面有输出，清除输出缓存
//生成图片
header ( 'Content-Type: image/png' );//header前不能加任何输出或加ob_clean()清除
imagepng($img);
//----4 销毁画布
imagedestroy($img);

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