警告：mysqli_select_db（）需要2个参数，1个给定* 13 * [重复]

Question

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• Warning: mysqli_select_db() expects exactly 2 parameters, 1 given [duplicate] 7 answers

I'm working on a system for my school that lets the teachers post any notices they have for the day on the intranet. However I got this error when testing it out:

Warning: mysqli_select_db() expects exactly 2 parameters, 1 given in C:\Users\Matthew\Desktop\wamp64\www\my-site\viewguestbook.php on line 23.

Here is the page's code:

<?php

$host="localhost"; // Host name 
$username="root"; // Mysql username 
$password=""; // Mysql password 
$db_name="test"; // Database name 
$tbl_name="guestbook"; // Table name 

// Connect to server and select database.
mysqli_connect("$host", "$username", "$password")or die("cannot connect server "); 
mysqli_select_db("$db_name")or die("cannot select DB");
$sql="SELECT * FROM $tbl_name";
$result=mysqli_query($sql);
while($rows=mysqli_fetch_array($result)){
?>

Note: This is different to the other questions of this same name on the website as it's in a different circumstance.

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Answer 1

The first parameter of mysqli_select_db() is connection object. This is the syntax :

mysqli_select_db(connection,dbname);

Change your code to:

$con = mysqli_connect("$host", "$username", "$password")or die("cannot connect server "); 
mysqli_select_db($con,$db_name)or die("cannot select DB");

Add the connection object as first parameter in mysqli_query and mysqli_fetch_array functions too. Please refer this link for the syntax.