function wp_loginout( $redirect = '', $echo = true ) {
if ( ! is_user_logged_in() ) {
    $link = '<a href="' . esc_url( wp_login_url( $redirect ) ) . '">' . __( 'Log in' ) . '</a>';
} else {
    $link = '<a href="' . esc_url( wp_logout_url( $redirect ) ) . '">' . __( 'Log out' ) . '</a>';
}

if ( $echo ) {
    /**
     * Filters the HTML output for the Log In/Log Out link.
     *
     * @since 1.5.0
     *
     * @param string $link The HTML link content.
     */
    echo apply_filters( 'loginout', $link );
} else {
    /** This filter is documented in wp-includes/general-template.php */
    return apply_filters( 'loginout', $link );
}

}

Displays a link, which allows users to navigate to the Log In page to log in or log out depending on whether they are currently logged in.

    function wp_loginout( $redirect = '', $echo = true ) {
    if ( ! is_user_logged_in() ) {
        $link = '<a href="' . esc_url( wp_login_url( $redirect ) ) . '">' . __( 'Log in' ) . '</a>';
    } else {
        $link = '<a href="' . esc_url( wp_logout_url( $redirect ) ) . '">' . __( 'Log out' ) . '</a>';
    }
 
    if ( $echo ) {
        /**
         * Filters the HTML output for the Log In/Log Out link.
         *
         * @since 1.5.0
         *
         * @param string $link The HTML link content.
         */
        echo apply_filters( 'loginout', $link );
    } else {
        /** This filter is documented in wp-includes/general-template.php */
        return apply_filters( 'loginout', $link );
    }
}

Displays a link, which allows users to navigate to the Log In page to log in or log out depending on whether they are currently logged in.