Difference between as $key => $value and as $value

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PART.one — — question:

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

   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:

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

this outputs the same as:       < From http://stackoverflow.com/  >

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

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

PART.two— — Answers

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.);

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.

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.

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.

转载于:https://my.oschina.net/yonglei/blog/294493