PHP函数默认参数值问题

 法 1： 默认参数值赋值给变量写在最上面

<?php 
$host=DB_HOST;
$user=DB_USER;
$password=DB_PASSWORD;
$database=DB_DATABASE;
$port=DB_PORT;

/* connect database */
function connect($host,$user,$password,$database,$port){
    $link=@mysqli_connect($host,$user,$password,$database,$port);
    if(mysqli_connect_errno()){
        exit(mysqli_connect_error());
    }
    mysqli_set_charset($link,'utf8');
    return $link;  
}

运行函数，函数要传参数：

<?php 
include_once '../inc/config.inc.php';
include_once '../inc/mysql.inc.php';
connect($host,$user,$password,$database,$port);

?>

法 2： 默认参数写在函数里面

<?php 
$host=DB_HOST;
$user=DB_USER;
$password=DB_PASSWORD;
$database=DB_DATABASE;
$port=DB_PORT;

/* connect database */
function connect($host=DB_HOST,$userDB_USER,$password=DB_PASSWORD,
$database=DB_DATABASE,$port=DB_PORT){
    $link=@mysqli_connect($host,$user,$password,$database,$port);
    if(mysqli_connect_errno()){
        exit(mysqli_connect_error());
    }
    mysqli_set_charset($link,'utf8');
    return $link;  
}

运行函数，函数可不传参数：

<?php 
include_once '../inc/config.inc.php';
include_once '../inc/mysql.inc.php';
connect();

?>