PHP使用include（）變量作用域問題

Question

我對commong函數有commonFun.php;

<?php 

function connectDB(){ 
    $con = @mysqli_connect("localhost:3306", "root", "P@ssw0rd", "DogSport") or die ("Couldn't connect to server"); 
} 

//check that email is not already in list 
function emailChecker($email){ 
    connectDB(); 

    $safe_email = mysqli_real_escape_string($con, $email); 
    $check_sql = "SELECT Id FROM Subscribers WHERE Email='". $safe_email. "'"; 

    $result = mysqli_query ($con, $check_sql) or die ("Couldn't execute SELECT query: ". mysqli_error($con)); 
} 
?> 

當我打電話emailChecker（）函數從另一個PHP腳本，爲什麼在connectDB（）$ CON變量不可用於emailChecker（）函數？我已經在emailChecker（）函數中調用connectDB（）函數了？我究竟做錯了什麼？？？？？

我得到以下錯誤;

Notice: Undefined variable: con in C:\xampp\htdocs\PHP\commonFun.php on line 11 

Warning: mysqli_real_escape_string() expects parameter 1 to be mysqli, null given in C:\xampp\htdocs\PHP\commonFun.php on line 11 

Notice: Undefined variable: con in C:\xampp\htdocs\PHP\commonFun.php on line 14 

Warning: mysqli_query() expects parameter 1 to be mysqli, null given in C:\xampp\htdocs\PHP\commonFun.php on line 14 

Notice: Undefined variable: con in C:\xampp\htdocs\PHP\commonFun.php on line 14 

Warning: mysqli_error() expects parameter 1 to be mysqli, null given in C:\xampp\htdocs\PHP\commonFun.php on line 14 
Couldn't execute SELECT query: 

Answer 1

功能connectDB（）{

$ CON = @mysqli_connect（ 「本地主機：3306」， 「根」， 「P @ ssw0rd」， 「DogSport」）或死亡（「無法連接到服務器「）;

return $ con; }

Answer 2

壞的解決方案，但它會工作：

function connectDB(){ 
    global $con; 

    $con = @mysqli_connect("localhost:3306", "root", "P@ssw0rd", "DogSport") or die ("Couldn't connect to server"); 
} 

//check that email is not already in list 
function emailChecker($email){ 
    global $con; 

    connectDB(); 

    $safe_email = mysqli_real_escape_string($con, $email); 
    $check_sql = "SELECT Id FROM Subscribers WHERE Email='". $safe_email. "'"; 

    $result = mysqli_query ($con, $check_sql) or die ("Couldn't execute SELECT query: ". mysqli_error($con)); 
} 

另一種解決方案：

$con = @mysqli_connect("localhost:3306", "root", "P@ssw0rd", "DogSport") or die ("Couldn't connect to server"); 

//check that email is not already in list 
function emailChecker($email){ 
    global $con; 

    $safe_email = mysqli_real_escape_string($con, $email); 
    $check_sql = "SELECT Id FROM Subscribers WHERE Email='". $safe_email. "'"; 

    $result = mysqli_query ($con, $check_sql) or die ("Couldn't execute SELECT query: ". mysqli_error($con)); 
} 

是不好的調用mysqli_connect（）在每一個函數調用腳本。每次執行頁面時，您只能連接到數據庫一次。