在PHP中奇怪的数组创建？ [英] Weird Array Creation in PHP?

问题描述

我读为mysqli_stmt_bind_result PHP手册看到在评论：

while ( $field = $meta->fetch_field() ) {
  $parameters[] = &$row[$field->name];
}

因为既不$ PARAMS也不$行这一行，为什么/如何做这一行工作的？

given that neither $params nor $row existed before that line, why/how does that line work?

推荐答案

PHP实际上并没有变量的声明。这意味着，在某些情况下，你可以参考变量，而实际上不必事先他们宣布。我说的有些是因为：

PHP doesn't actually have variable declaration. That means in some cases you can reference variables without actually having them declared beforehand. I say some cases because:

foreach($undefinedArray as $key=>$value){
    // will give a notice and a warning
    // notice: undefined variable
    // warning: invalid argument to foreach
}

但是，这并不意味着你不能做一些像这样：

But this doesn't mean you can't do something like so:

for($i=0;$i<5;$i++){
    $undefinedArray[]=$i;
}
// will create an array with 5 indexes, each holding the numbers 0 through 4

这工作，因为 $ undefinedArray 找不到创造的飞行。

This works because $undefinedArray is not found and created on the fly.

现在，关于你自己的情况。我会假设你的意思这个帖子。我不得不承认，这是一个非常有趣的解决方案，我要去尝试克制自己无法评论任何一种不好的做法的存在，但让我们坐上去解释它！

Now, regarding your own case. I'm gonna assume you mean this post. And I have to admit, that's a very interesting solution, I'm gonna try to restrain myself from commenting on any kind of bad practice there, but let's get on to explaining it!

$params[] = &$row[$field->name]; 

这是那里的奇迹发生，这实际上是由于与放大器;.因为＆安培;！$行['unknown_index'] ，实际的创建指数

This is where the magic happens and it's actually due to the &. Because &$row['unknown_index'], actually creates the index!

这意味着，上述说法做两件事情。首先，它创建与 $行保存为索引中的每一列名的数组（ $行[$现场＆GT;名称] ）。然后，它在 $ PARAMS 保存一个指针，每个元素从 $行。

This means that above statement does 2 things. First it creates an array with each column name saved as an index in $row ($row[$field->name]). Then it saves a pointer to each of the elements from $row in $params.

call_user_func_array(array($stmt, 'bind_result'), $params); 

这确实 $ stmt-＆GT; bind_result（）。但在 $ PARAMS 作为参数传递bind_result每个元素。而且因为他们是按引用传递，$行的各项指标将举行各自选定的领域。

This does $stmt->bind_result(). But passes each of the elements in $params as parameters to bind_result. And since they're passed by reference, each index of $row will hold each of the selected fields.

剩下的应该很容易，现在弄清楚。

The rest should be easy to figure out now.

如果你有任何问题。随意问！

If you got any questions. Feel free to ask!

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