如何通过使所有其他强制/可选参数（如果有的话）保持默认值，仅将可选参数传递给PHP函数？

Question

I'm using PHP 7.3.2 on my laptop that runs on Windows 10 Home Single Language 64-bit operating system .

I've installed the latest version of XAMPP installer on my laptop which has installed the Apache/2.4.38 (Win32) and PHP 7.3.2

Please do consider below prototype definition of the built-in PHP function htmlspecialchars() from the PHP Manual :

htmlspecialchars ( string $string [, int $flags = ENT_COMPAT | ENT_HTML401 [, string $encoding = ini_get("default_charset") [, bool $double_encode = TRUE ]]] ) : string

Now, I only want to set the last optional parameter ie $double_encode with a boolean value FALSE and keep all other optional parameters set to their default values.

For achieving this I tried below code :

<?php
  echo htmlspecialchars('&amp', '', '', FALSE);
?>

After executing the above code I got following output in my web browser :

Warning: htmlspecialchars() expects parameter 2 to be int, string given in th67i.php on line 2

I'm not understanding where I'm going wrong. I took care of other parameters to be set to their default values by keeping blank spaces separated by commas and only assigning the optional parameter $double_encode to boolean value FALSE .

Then why I'm not able to get the output and getting some warning? Why? What mistake I'm making in my code?

Please help me out from this problem.

Thanks in advance.

Answer 1

Passing '' does not mean falling back to default argument value. It means just that — trying to pass an empty string.

You would need to reproduce defaults if you want to achieve this:

htmlspecialchars('&amp', ENT_COMPAT | ENT_HTML401, ini_get('default_charset'), FALSE);