Solution to the problem that the PHP verification code image cannot be displayed

Today, I created a new virtual host locally and deployed a small PHP website that I wrote before. Because I used the wamp integrated environment before, this situation did not occur. Now I suddenly find that the verification code cannot be generated.

So I started my journey to find bugs. I searched many ways on the Internet and finally solved it. Now I share it as follows:

bug1

When the above situation occurs, the most basic mistake is that you may have forgotten to install the gd module in php. (Recommended learning: PHP video tutorial)

In the window environment, you only need to find

;extension=php_gd2.dll

in the php.ini file and remove the semicolon in front of it, then restart After apache, you can find this in phpinfo()

If you are in the ubuntu environment, you need to install the gd module, the command is

sudo apt-get install php5-gd

After installation, also You can see the module above.

bug2

If you go through the above installation and find that it still doesn’t work, then it may be the following problem

Your code It is probably edited using a text editor like editpuls or notepad, so their default encoding format is UTF-8 with BOM.

UTF-8 BOM is also called UTF-8 signature. In fact, the BOM of UTF-8 has no effect on UFT-8. It is added to support UTF-16 and UTF-32. The meaning of BOM signature is It just tells the editor what encoding the current file uses to facilitate the editor's identification. However, although the BOM is not displayed in the editor, it will produce output, just like an extra blank line.

Generally I use UTF-8 BOM-free format

So you need to change the encoding format of the code to BOM-free format.

bug3

If you go through the above two steps and find that it still doesn’t work, then you have to use your trump card.

Use ob_clean() to clear the cache.

The function of ob_clean is to discard the contents of the output buffer. If you have many generated image files, you must clear the buffer frequently if you want to access them correctly.

public function create()
{
ob_clean();
$a = new verify();
session::set('captcha', strtolower($a->create(4, 15)));
view::assign("captcha", $a);
view::display("captcha");
exit(0);
}

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