为什么我的变量在TCPDF中没有定义?

My Sql Table

我的Sql表

+------------+---------+
|    name    |  price  |
+------------+---------+
|     A      |    70   |
+------------+---------+
|     B      |    70   |
+------------+---------+

I create a pdf with TCPDF:

我用TCPDF创建一个pdf:

$pdo = $db->prepare("SELECT * FROM table");  
    $pdo->execute(); 
    while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {  
        $result += $row['price'];       
} 

$html = '
<table><tr><th>'.$result.'</th></tr></table>'
;

I expect the result to be 140, but I get an error message:

我希望结果是140，但是我得到了一个错误信息:

Notice: Undefined variable: result 
TCPDF ERROR: Some data has already been output, can't send PDF file

Note: If I remove the + sign. The pdf is created without errors and I get the result 70.

注意:如果我删除+号。pdf是在没有错误的情况下创建的，我得到的结果是70。

2 个解决方案

#1

It does what it says on the tin: $result is not defined the first time you loop through your data. You can't add anything to it, because it's not defined yet. This should work.

它执行它在tin上的操作:$result在您第一次循环数据时没有定义。你不能添加任何东西，因为它还没有定义。这应该工作。

$pdo = $db->prepare("SELECT * FROM table");  
    $pdo->execute(); 
    $result = 0.0; // Add this row. I'm assuming 'price' is a decimal
    while ($row = $pdo->fetch(PDO::FETCH_ASSOC)) {  
        $result += $row['price'];       
    }

#2

On the line

在直线上

$result += $row['price'];

You make this

你做这个

$result = $result + $row['price'];

But the very first time you run the script, the $result variable is not defined. Add

但是第一次运行脚本时，$result变量没有定义。添加

$result = 0;

before the $pdo connection or before the while and you should not have any errors anymore.

在$pdo连接之前或之前，您应该不会再有任何错误。

#1