domain lowercase

const QString tempstring1 =
        "^"
        // Identifier for http and ftp
        "(?:(?:https?|ftps?)://)?"
        // user:pass authentication
        "(?:\\S+(?::\\S*)?@)?"
        "(?:"
        // IP address dotted notation octets
        // excludes loopback network 0.0.0.0
        // excludes reserved space >= 224.0.0.0
        // excludes network & broacast addresses
        // (first & last IP address of each class)
        "(?:[1-9]\\d?|1\\d\\d|2[01]\\d|22[0-3])"
        "(?:\\.(?:1?\\d{1,2}|2[0-4]\\d|25[0-5])){2}"
        "(?:\\.(?:[1-9]\\d?|1\\d\\d|2[0-4]\\d|25[0-4]))"
        "|"
        // host name
        "(?:(?:[_a-z\\x{00a1}-\\x{ffff}0-9]-*)*[a-z\\x{00a1}-\\x{ffff}0-9]+)"
        // domain name
        "(?:\\.(?:[a-z\\x{00a1}-\\x{ffff}0-9]-*)*[a-z\\x{00a1}-\\x{ffff}0-9]+)*"
        // TLD identifier
        "(?:\\.(?:[a-z\\x{00a1}-\\x{ffff}]{2,}))"
        "\\.?"
        ")"
        // port number
        "(?::\\d{2,5})?";
QRegularExpression getDomain(tempstring1, QRegularExpression::CaseInsensitiveOption);
QString tempString = string;
QString domain = getDomain.match(tempString).captured(0);
QString lowercaseLinkString = string;
lowercaseLinkString.replace(domain, domain.toLower());