php foreach 指针

Question

$arr = array('a', 'b', 'c');$i = 0;foreach($arr as $key =&gt; $value) { {代码...} }//$arr的指针被移动了一次，指向第二个元素b上。var_dump(current($arr));//b 为什么一开始指针就到第二个元素去了

天蓬老师 · Answer

$arr = array('a', 'b', 'c');
$i = 0;
foreach($arr as $key => $value) {
    if($i == 0) {
        $arr[$key] = $value . $value;
    }
    $i++;
}

伪代码形同

$arr = array('a', 'b', 'c');
$i = 0;
$arrCopy = $arr; //复制出一个待循环数组的副本，接下来都是操作这个副本
$key = currentKey($arrCopy); //将获取到的值分配给$k;
$val = currentVal($arrCopy); //将获取到的值分配给$v;

//移动副本数组的指针,这边执行顺序比写时复制高，所以先移动
next($arrCopy);
$arr = $arrCopy;//将副本赋值回给$arr（（主要是将指针同步移动））

{ //大括号的内容
    if($i == 0) {
        $arr[$key] = $value . $value;
    }
    $i++;
}


//然后第二次循环
$key = currentKey($arrCopy); 
$val = currentVal($arrCopy);
//移动副本数组的指针,这边执行顺序比写时复制高，所以先移动
next($arrCopy);
$arr = $arrCopy;//将副本赋值回给$arr（（主要是将指针同步移动））

{ //大括号的内容
    if($i == 0) {
        $arr[$key] = $value . $value;
    }
    $i++;
}
//然后第三次循环
$key = currentKey($arrCopy); 
$val = currentVal($arrCopy);
//移动副本数组的指针,这边执行顺序比写时复制高，所以先移动
next($arrCopy);
$arr = $arrCopy;//将副本赋值回给$arr（（主要是将指针同步移动））

{ //大括号的内容
    if($i == 0) {
        $arr[$key] = $value . $value;
    }
    $i++;
}

天蓬老师 · Answer

 $key = currentKey($arrCopy); //将获取到的值分配给$k;
 $val = currentVal($arrCopy); //将获取到的值分配给$v;
 next($arrCopy);//移动副本数组的指针
 $arr = $arrCopy;//将副本赋值回给$arr（（主要是将指针同步移动））

当本次赋值给key和val之后，按照流程指针已经向下移动了一位，所以当执行var_dump(current($arr));时打印false

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