<form action="" method="post">

    <select name="host">

        <option value="localhost" selected>localhost</option>

        <option value="127.0.0.1">127.0.0.1</option>

    </select>

    <br><br>

    user:<input type="text" name="user" value=""><br><br>

    pwd :<input type="password" name="pwd" value=""><br><br>

    <input type="submit" value="connent">

    <input type="reset" value="reset">

</form>

<?php

    error_reporting(~E_ALL);

    $host = $_POST['host'];

    $user = $_POST['user'];

    $pwd = $_POST['pwd'];

    if(isset($_POST['host']) && isset($_POST['user']) && isset($_POST['pwd'])){

        if(strlen($host)<1 or strlen($user)<1 or strlen($pwd)<1){

            echo "请完善相关数据库链接信息。";

            exit(0);

        }

        $conn = mysql_connect($host, $user, $pwd) or die("Error-数据库连接失败！");

        if($conn){

            echo "OK—数据库连接成功！";

        }

    }

?>