The picture verification code developed by PHP fails to display

1. Install the gd module

In the window environment, you only need to find ";extension=php_gd2.dll" in the php.ini file. Just remove the semicolon in front of it. After restarting apache, you can find the gd information 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, you can also see the above module.

2. Confirm the encoding of the code file

If it is utf-8 with BOM, it needs to be changed to a BOM-free format.

3. Use ob_clean() to clear the cache.

The function of ob_clean is to discard the output buffer. If you have many generated image files, you need to 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);
    }

4. PHP version problem

If you use a higher PHP version, you cannot use undefined variables, otherwise a notice error will be reported, $ New_number and $_SESSION['check_checks'] must be judged by isset before use, or if you use old code, add error_reporting(E_ALL & ~E_NOTICE); to shield the notice error (not recommended) ),
So use isset() to check to make sure it is defined.

If it’s not solved?

Through debugging, I found that the verification code was not displayed because the font file could not be found.

$font="simhei.ttf"

is written as a relative path, and the font file needs to be placed in the project. Or write the absolute path to the system font file.
I put it in the lib folder:

$font=LIB_PATH."simhei.ttf"

Recommended tutorial: PHP tutorial

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