PHP next

1.函數的做用：返回數組當前元素位置的下一個元素

2.函數的參數：

　　@param array &$array

3.

例子一：數組拷貝時，內部指針的位置也一塊兒拷貝

1 <?php
2 $arr1 = ['last','next'];
3 next($arr1);
4 $arr2 = $arr1;
5 echo "Pointer of arr1 is " .key($arr1) .". The value is '" . current($arr1) ."'\n";
6 echo "Pointer of arr2 is " .key($arr2) .". The value is '" . current($arr1) ."'\n";

 

例子二： foreach 以後數組內部指針的位置不重置

1 <?php
2 $arr1 = ['last','next'];
3 foreach($arr1 as $key => $value){
4     echo "Number $key's  value : $value\n";
5 }
6 $str = is_null(key($arr1));
7 echo "The current key of the array of arr1 is " . ($str ? 'null' : $str) ;

 例子三：

1 <?php
2 $arr1 = ['last','next'];
3 next($arr1);
4 $arr2 = array_values($arr1);
5 
6 echo "The pointer's position of the array of arr1 is " .key($arr1) . "\n";
7 echo "The pointer's position of the array of arr1 is " .key($arr2) . "\n";

 例子四：接下來是比較奇異的兩個地方，傳數組參數給函數，看看指針的位置的狀況：

1）指針重置的狀況：

1 <?php
2 function testPointerPosition($array){
3     echo "The current element of array in function is '" .current($array)."' and current key is " .key($array)."\n";
4 }
5 
6 $arr1 = ['last','next'];
7 next($arr1);
8 next($arr1);
9 testPointerPosition($arr1);

2）指針未重置的狀況：

1 <?php
2 function testPointerPosition($array){
3     echo "The current element of array in function is '" .current($array)."' and current key is " .key($array)."\n";
4 }
5 
6 $arr1 = ['last','next'];
7 next($arr1);
8 testPointerPosition($arr1);

 

例子五：有的時候使用next()函數以後，你想判斷該元素是否是存在，結果你這麼用：

1 <?php
2 $arr = [1,false];
3 next($arr);
4 if(current($arr)){
5     echo "The element exist!\n";
6 }else{
7     echo "The element doesn't exist!\n";
8 }

恰好有個 false 元素，就有了錯誤的輸出。因此應該這麼用：

1 <?php
2 $arr = [1,false];
3 next($arr);
4 if(key($arr) === false){
5     echo "Current element doesn't exist!\n";
6 }else{
7     echo "Current element exist!\n";
8 }

 

記住用 「===」 符號。數組不會有鍵值爲false的類型的，即便你初始化的時候，用false做鍵值，內部也會將其解釋爲 0，並覆蓋先前的鍵值爲 0 的元素。