为什么不能我把元素添加到在foreach循环子阵？ [英] Why cant i push element onto sub array in foreach loop?

问题描述

我想了解一些有关在每个循环中的数组可能是明显的多。

I'm trying to understand something about arrays in for each loops that might be obvious to many.

当通过我的多维数组i循环，我试图找到没有第三元件子阵列。如果他们没有第三元件，我要到第三元素添加到该子阵列与一个特定的值。

When i loop through my multi-dimensional array, i attempt to find sub arrays with no third element. If they have no third element, i want to add a third element to that sub array with a specific value.

$testArray = array (
    array("Green", "Yellow", "Blue"),
    array("Brown", "Silver"),
    array("Orange", "Pink", "Black"),
);

当我使用foreach循环：

When i use the foreach loop:

foreach ( $testArray as $key => $array ) {
    if (count($array) == '2') {
        $array[] = "None";
    };
}

没有错误抛出，但没有任何反应。当我使用的每一个循环：

No errors are thrown but nothing happens. When i use the for each loop:

foreach ( $testArray as $key => $array ) {
    if (count($array) == '2') {
        $testArray[$key][] = "None";
    };
}

它按预期工作。

很抱歉的长期preamble，我的问题是：

Sorry for the long preamble, my questions is:

为什么没有这两个foreach循环做同样的事情？谢谢！

Why aren't these two foreach loops doing the same thing? Thanks!

推荐答案

这里的问题在于，超过iterables的foreach迭代和值设置迭代变量。这意味着 $阵列您要在处理的foreach 不是<$ C的值相同$ C> $ testArray 。

The problem here lies in the fact that foreach iterates over iterables and sets the iteration variable by value. This means that the $array which you are dealing with in the foreach is not the same value of the $testArray.

要rememdy这（和避免引入一个 $指数变量变异数组中的一个项目），你需要告诉的foreach来的通过引用传递中的价值。引用是PHP的答案C风格的指针。如果一个变量引用另一个，这两个变量指向相同的值，因此一个的内容的修改是有效的其他的变形例。在你的的foreach ，您可以用＆放大器; $阵列有循环传给你<$ C $的项目C> $ testArray ：

To rememdy this (and avoid introducing an $index variable to mutate an item in the array), you will need to tell foreach to pass the value by reference. References are PHP's answer to C-style pointers. If a variable references another, both variables point to the same value, so a modification to the contents of one is in effect a modification to the other. In your foreach, you can use &$array to have the loop pass you the items of $testArray by reference instead of by value:

foreach ( $testArray as $key => &$array ) {
    if (count($array) == '2') {
        $array[] = "None";
    }
}

（ codePAD演示）

这对齐与PHP的引用，在哪里可以取得一个变量引用另一个像这样：

This aligns with PHP's references, where one variable can be made to reference another like so:

$a = array(1, 2, 3);
$b = &$a;
$b[] = 4;

print_r($a); // 1, 2, 3, 4

（ codePAD演示）

您遇到类似现象与功能：

You experience a similar phenomenon with functions:

function byValue($a) {
    $a[] = 4;
}

function byRef(&$a) {
    $a[] = 5;
}

$a = array(1, 2, 3);

byValue($a);
print_r($a); // 1, 2, 3

byRef($a);
print_r($a); // 1, 2, 3, 5

（ codePAD演示）

借助引用文档PHP的部分有对此问题的一些例子的foreach 的语法。还要注意这个（有点）有关，但在的foreach 有趣的阅读和引用的。

The references section of the PHP docs has some examples about this syntax of foreach. Also note this (somewhat) related, but interesting read on foreach and references.

此外，在一个不相关的音符，如果你不知道：你不需要关闭块后用分号} 在PHP中，除非你正在做的事就像给一个变量分配一个封闭：

Also, on an unrelated note if you weren't aware: you don't need a semicolon after closing a block with } in PHP unless you're doing something like assigning a closure to a variable:

$someFunc = function($a) { return $a; }; //need one here

if(1 + 2 == 4) {
   echo "I just broke math";
} // but you don't need one here

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