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

例子一：数组拷贝时，内部指针的位置也一起拷贝

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

例子二： foreach 之后数组内部指针的位置不重置

1 <?php
2 $arr1 = ['last','next'];
3 foreach($arr1 as $key => $value){
4     echo "Number $key's  value : $value
";
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($arr1) . "
";
7 echo "The pointer's position of the array of arr1 is " .key($arr2) . "
";

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：

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

2）指针未重置的情况：

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

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

刚好有个 false 元素，就有了错误的输出。所以应该这么用：

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

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。

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