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变量的变量PHP 和 你

在我最近做的一个项目中我发现了一个新的概念关于在PHP中使用变量的变量。在我的程序中我需要在一个页面同时更新多个记录在我经过相当长时间的痛苦思索之后脑海中偶然地闪现出了变量的变量variable variable这一概念所有的困惑就一扫而光了。

介绍

什么叫作变量的变量根据PHP手册变量的变量是指取得一个变量的值并把它作为另一个变量的变量名。这表述显得相当的直接容易和那些在一个句子中使用“变量”这个词弄混淆。给一个简单的例子你定义一个变量 --- x 等于 this --- 然后定义一个变量的变量意味着你把 x 的值作为新变量的名在这个例子中这个新变量的值是 is cake。用PHP来表示如下


$x = "this";
$$x = "is cake";

?>

这个符号$$是在PHP中对变量的变量的表示方法。现在我们可以用两种不同的方式来引用这两个变量 $x 和 $$x 了。


echo "$x ${$x}";

?>


echo "$x $this";

?>

上面两段程序都将输出 this is cake。注意echo语句中$$x被写成${$x}这是让PHP知道你要输出的是变量的变量而不是一个$字符与$x变量。

你是不是仍很迷惑也许吧你想要一些更深入更有用的例子下一节我将向你展示怎样用变量的变量在一个页面编辑多条记录的。


例子

假设你已有一个MySQL数据库保存了对一些感兴趣的站点的链接库中有一个表submissions字段如下

SubmissionID
PostedBy
Link
Description
Approved

现在你想显示在表中所有的已创建但没有被认可的链接这个编辑的页面应可以更正一些输入时的错误并用适当的单选按钮来为每一个记录设置是否允许(Approved)然后一次把更新后的记录都提交到表中。

首先当你从数据库出提取所有的记录并显示出来时你必须为每一个记录设置一个唯一的名字这将让我们在提交时可以循环地辩别出各个记录的值。代码如下


//初始化变量的记数器

$index = 0;
$index_count = 0;

echo "

n"
;
echo "n";
echo"".
"
n";


/*********
假定我们已从数据库中检索出记录到一个数组中 
$myrow = mysql_fetch_array().
下面的 do...while 循环根据名字为每一个$xstr变量分配了一个值并且连接了$index 的值到结尾,以0为开始。
这样,这个循环的第一次时,$SubmissionIDStr 的值就是 SubmissionID0 ,第二次就是 SubmissionID1 ,以此类推。
***********/


do{

$SubmissionIDStr = SubmissionID.$index;
$PostedByStr = PostedBy.$index;
$LinkStr = Link.$index;
$DescriptionStr = Description.$index;
$ApprovedStr = Aprroved.$index;


//这一段将在屏幕上显示值以每行一条记录。

printf("

n",
$SubmissionIDStr, $myrow["SubmissionID"], $PostedByStr, $myrow["PostedBy"], $LinkStr, $myrow["Link"],
$DescriptionStr, $myrow["Description"], $ApprovedStr, $ApprovedStr);


//每个循环记数器加1

$index++;
$index_count++;

}while($myrow = mysql_fetch_array($result));

// 创建一个索引记数器index_count来跟踪所有的记录数

echo"n";

echo"n";

?>

提交以后我们利用$index_count变量再一次循环遍历页面上所有的变量然后分配这些变量给另一些变量这就用到了变量的变量。


//这个循环遍历所有页面上显示的记录

for($index = 0; $index = $counter; $index++) {


/*****
这部分用我们在前面创建的名字设置了新的变量
从0开始,直到$index_count
*****/


$varSubmissionID = 'SubmissionID'.$index;
$varPostedBy = 'PostedBy'.$index;
$varLink = 'Link'.$index;
$varDescription = 'Description'.$index;
$varApproved = 'Approved'.$index;


/******
这是变量的变量部分,把每个值分配给每个新变量的名。
例如,第一次循环时,分配给记录 SubmissionID0 是从前面得来的值,我们用变量的变量来了取到它。
*******/


$SubmissionIDvalue = $$varSubmissionID;
$PostedByvalue = $$varPostedBy;
$Linkvalue = $$varLink;
$Descriptionvalue = $$varDescription;
$Approvedvalue = $$varApproved;


//更新数据库

$sql = "UPDATE submissions SET PostedBy='$PostedByvalue',Link='$Linkvalue',".
"Description='$Descriptionvalue' WHERE SubmissionID=$SubmissionIDvalue'";
$result = mysql_query($sql);


//如果本记录被设置为approved,更新相应的字段 Approved。

if ($Approvedvalue == '-1') {
$sql = "UPDATE submissions SET Approved='-1' WHERE SubmissionID=$SubmissionIDvalue";
$result = mysql_query($sql);
}

}

?>

我希望这有助于你明白这个变量的变量的基本用法并且在你将来的工作中使用它们提供一些思路。变量的变量这一概念最初也是让我头痛的东西但是一旦你知道了它们工作的基本原理时它们就变成了一块美味的比萨饼。如果有什么问题请让我知道吧。
Posted By LinkDescription Approved
YesNo

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