問題描述

我有一個(gè)數(shù)據(jù)庫調(diào)用，我想弄清楚 $key =>$value 在 foreach 循環(huán)中執(zhí)行.

I have a database call and I'm trying to figure out what the $key => $value does in a foreach loop.

我問的原因是因?yàn)檫@兩個(gè)代碼輸出相同的東西，所以我試圖理解為什么它是這樣寫的.代碼如下:

The reason I ask is because both these codes output the same thing, so I'm trying to understand why it's written this way. Here's the code:

1)在foreach中使用$key =>$value

1)In foreach use $key => $value

foreach($featured as $key => $value){
  echo $value['name'];
}

這個(gè)輸出與:

2)在 foreach 中只使用 $value

2)In foreach use only $value

foreach($featured as $value) {
  echo $value['name'];
}

所以我的問題是，$key => 和有什么區(qū)別?$value 或 $value 在 foreach 循環(huán)中.如果這有所不同，數(shù)組是多維的，我只想知道為什么在 foreach 循環(huán)中將 $key 傳遞給 $value.

So my question is, what is the difference between $key => $value or just $value in the foreach loop. The array is multidimensional if that makes a difference, I just want to know why to pass $key to $value in the foreach loop.

推薦答案

好吧，$key =>foreach 循環(huán)中的 $value 指的是關(guān)聯(lián)數(shù)組中的鍵值對(duì)，其中鍵作為索引來確定值，而不是像 0,1,2,... 這樣的數(shù)字在 PHP 中，關(guān)聯(lián)數(shù)組看起來像這樣:

Well, the $key => $value in the foreach loop refers to the key-value pairs in associative arrays, where the key serves as the index to determine the value instead of a number like 0,1,2,... In PHP, associative arrays look like this:

$featured = array('key1' => 'value1', 'key2' => 'value2', etc.);

在 PHP 代碼中:$featured 是循環(huán)遍歷的關(guān)聯(lián)數(shù)組，as $key =>$value 表示每次循環(huán)運(yùn)行并從數(shù)組中選擇一個(gè)鍵值對(duì)時(shí)，它將鍵存儲(chǔ)在本地 $key 變量中以在循環(huán)塊內(nèi)使用和值在本地 $value 變量中.因此，對(duì)于我們上面的示例數(shù)組，foreach 循環(huán)將到達(dá)第一個(gè)鍵值對(duì)，如果您將 指定為 $key =>;$value，它會(huì)將 'key1' 存儲(chǔ)在 $key 變量中，將 'value1' 存儲(chǔ)在 $value 中 變量.

In the PHP code: $featured is the associative array being looped through, and as $key => $value means that each time the loop runs and selects a key-value pair from the array, it stores the key in the local $key variable to use inside the loop block and the value in the local $value variable. So for our example array above, the foreach loop would reach the first key-value pair, and if you specified as $key => $value, it would store 'key1' in the $key variable and 'value1' in the $value variable.

由于您不在循環(huán)塊中使用 $key 變量，因此添加或刪除它不會(huì)改變循環(huán)的輸出，但最好包含鍵值對(duì)表明它是一個(gè)關(guān)聯(lián)數(shù)組.

Since you don't use the $key variable inside your loop block, adding it or removing it doesn't change the output of the loop, but it's best to include the key-value pair to show that it's an associative array.

還要注意 as $key =>$value 指定是任意的.您可以將其替換為 as $foo =>$bar 并且只要您將循環(huán)塊內(nèi)的變量引用更改為新變量 $foo 和 $bar，它就可以正常工作.但是讓它們成為 $key 和 $value 有助于跟蹤它們的含義.

Also note that the as $key => $value designation is arbitrary. You could replace that with as $foo => $bar and it would work fine as long as you changed the variable references inside the loop block to the new variables, $foo and $bar. But making them $key and $value helps to keep track of what they mean.

這篇關(guān)于"as $key => 之間的區(qū)別$值"和“作為 $value"在 PHP foreach 中的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！