Detailed explanation of PHP foreach principle

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PHP foreach principle detailed explanation

• When foreach starts executing, the pointer inside the array will automatically point to the first unit. This means there is no need to call reset() before the foreach loop. How to understand this?

$arr = array(1,2,3);foreach($arr as $k=>$v){

}
var_dump(current($arr));foreach($arr as $key=>$value){    echo $value." ";
}
var_dump(current($arr));

结果：boolean false

     1 2 3

     boolean false

• Deepen the understanding of foreach

$arr = array(&#39;a&#39;=>1,&#39;b&#39;=>2,&#39;c&#39;=>3);foreach($arr as $k=>$v){    $v*=2;    echo $v."<br />";
}
var_dump($arr);foreach($arr as $key=>$value){    $arr[$key]=$value*2;
}
var_dump($arr);//传入&foreach($arr as &$v){    $v=$v*2;
}$v = 0

var_dump($arr)

Result

246array (size=3)  'a' => int 1
  'b' => int 2
  'c' => int 3array (size=3)  'a' => int 2
  'b' => int 4
  'c' => int 6array (size=3) (不加 $v = 0)  'a' => int 4
  'b' => int 8
  'c' => &int 12array (size=3) (加 $v = 0)  'a' => int 4
  'b' => int 8
  'c' => 0

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