已弃用的 strlen（）：将 null 传递给字符串类型的参数 #1 （$string） 已弃用

问：

your text

从 PHP 7.4 升级后，在 PHP 8.1 中显示上述警告

关于如何更改此代码以实现 PHP 8.1 兼容性的任何想法？

   private function cleanInput2($strRawText, $strAllowableChars, $blnAllowAccentedChars)
    {
        $iCharPos = 0;
        $chrThisChar = "";
        $strCleanedText = "";

        //Compare each character based on list of acceptable characters
        while ($iCharPos < strlen($strRawText))
        {
            // Only include valid characters **
            $chrThisChar = substr($strRawText, $iCharPos, 1);
            if (strpos($strAllowableChars, $chrThisChar) !== FALSE)
            {
                $strCleanedText = $strCleanedText . $chrThisChar;
            }
            elseIf ($blnAllowAccentedChars == TRUE)
            {
                // Allow accented characters and most high order bit chars which are harmless **
                if (ord($chrThisChar) >= 191)
                {
                    $strCleanedText = $strCleanedText . $chrThisChar;
                }
            }

            $iCharPos = $iCharPos + 1;
        }

        return $strCleanedText;
    }