PHP next

1.函数的作用：返回数组当前元素位置的下一个元素

2.函数的参数：

　　@param array &$array

3.

例子一：数组拷贝时，内部指针的位置也一起拷贝

 <?php
 $arr1 = ['last','next'];
 next($arr1);
 $arr2 = $arr1;
 echo "Pointer of arr1 is " .key($arr1) .". The value is '" . current($arr1) ."'\n";
 echo "Pointer of arr2 is " .key($arr2) .". The value is '" . current($arr1) ."'\n";

例子二： foreach 之后数组内部指针的位置不重置

 <?php
 $arr1 = ['last','next'];
 foreach($arr1 as $key => $value){
     echo "Number $key's  value : $value\n";
 }
 $str = is_null(key($arr1));
 echo "The current key of the array of arr1 is " . ($str ? 'null' : $str) ;

例子三：

 <?php
 $arr1 = ['last','next'];
 next($arr1);
 $arr2 = array_values($arr1);
 
 echo "The pointer's position of the array of arr1 is " .key($arr1) . "\n";
 echo "The pointer's position of the array of arr1 is " .key($arr2) . "\n";

例子四：接下来是比较奇异的两个地方，传数组参数给函数，看看指针的位置的情况：

1）指针重置的情况：

 <?php
 function testPointerPosition($array){
     echo "The current element of array in function is '" .current($array)."' and current key is " .key($array)."\n";
 }
 
 $arr1 = ['last','next'];
 next($arr1);
 next($arr1);
 testPointerPosition($arr1);

2）指针未重置的情况：

 <?php
 function testPointerPosition($array){
     echo "The current element of array in function is '" .current($array)."' and current key is " .key($array)."\n";
 }
 
 $arr1 = ['last','next'];
 next($arr1);
 testPointerPosition($arr1);

例子五：有的时候使用next()函数之后，你想判断该元素是不是存在，结果你这么用：

 <?php
 $arr = [1,false];
 next($arr);
 if(current($arr)){
     echo "The element exist!\n";
 }else{
     echo "The element doesn't exist!\n";
 }

刚好有个 false 元素，就有了错误的输出。所以应该这么用：

 <?php
 $arr = [1,false];
 next($arr);
 if(key($arr) === false){
     echo "Current element doesn't exist!\n";
 }else{
     echo "Current element exist!\n";
 }

记住用 “===” 符号。数组不会有键值为false的类型的，即使你初始化的时候，用false作键值，内部也会将其解释为 0，并覆盖先前的键值为 0 的元素。