PHP无法重新声明函数/未定义函数的调用

Question

I am using WooCommerce on Wordpress 4.7.1. Previously, I was running 4.7.0. When Wordpress automatically upgraded to 4.7.1, I suddenly began seeing checkouts fail to redirect to the "Thank you" page, and the UI showed that a fatal error had occurred.

Turning on debugging revealed the following error:

PHP Fatal error: Cannot redeclare get_cc() (previously declared in .../templates/emails/email-addresses.php:36) in .../templates/emails/email-addresses.php on line 36

I also confirmed that this file is never directly called with require , require_once , include , or include_once . It is, however, called with wc_get_template() .

A quick search brought me to this similar question . So I added the following to email-addresses.php:

if (!function_exists('get_cc')) {
    function get_cc( $code ) {
        ... function body
    }
}

After making this change, I now receive the following error in the debug log:

PHP Fatal error: Call to undefined function get_cc() in .../templates/emails/email-addresses.php on line 32

This means that, for whatever reason, PHP believes that the function get_cc already exists, but at the same time it is undefined.

I was not the original developer. I took over the project from a contractor who is not available. It does seem clear that this file is heavily modified from the original. I am certain that the value returned by the function must be kept, so I cannot just comment out the call.

Given the information above, what options do I have to either workaround or fix this issue?

Answer 1

It turns out that, unlike a standard function definition in PHP, function definitions wrapped in if (!function_exists('function_name')) { ... } block must precede any call to that function .

In this case, the function definition (line 36) followed the call (line 32). This caused the function to appear to PHP as undefined:

// Not working!
$value = get_cc($code);

if (!function_exists('get_cc')) {
    function get_cc( $code ) {
        ... 
    }
}

Switching the order so that the function definition came first fixed the issue:

// Working!
if (!function_exists('get_cc')) {
    function get_cc( $code ) {
        ... 
    }
}

$value = get_cc($code);

As of right now, PHP's documentation does not mention this issue.