Question

为什么：

$test_obj = new stdClass(); 
$array = [];
for ($i=0; $i < 5; $i++) { 
    $test_obj->num = $i;
    array_push($array, $test_obj);
}
var_dump($array);

产生

array(5) {
  [0] =>
  class stdClass#1 (1) {
    public $num =>
    int(4)
  }
  [1] =>
  class stdClass#1 (1) {
    public $num =>
    int(4)
  }
  [2] =>
  class stdClass#1 (1) {
    public $num =>
    int(4)
  }
  [3] =>
  class stdClass#1 (1) {
    public $num =>
    int(4)
  }
  [4] =>
  class stdClass#1 (1) {
    public $num =>
    int(4)
  }
}

和

$array = [];
for ($i=0; $i < 5; $i++) { 
    $test_obj = new stdClass(); 
    $test_obj->num = $i;
    array_push($array, $test_obj);
}
var_dump($array);

产生

array(5) {
  [0] =>
  class stdClass#1 (1) {
    public $num =>
    int(0)
  }
  [1] =>
  class stdClass#2 (1) {
    public $num =>
    int(1)
  }
  [2] =>
  class stdClass#3 (1) {
    public $num =>
    int(2)
  }
  [3] =>
  class stdClass#4 (1) {
    public $num =>
    int(3)
  }
  [4] =>
  class stdClass#5 (1) {
    public $num =>
    int(4)
  }
}

可是：

$test_obj = new stdClass(); 
$array = [];
for ($i=0; $i < 5; $i++) { 

    $test_obj->num = $i;
    array_push($array, $test_obj);
    var_dump($test_obj);
}

产生

class stdClass#1 (1) {
  public $num =>
  int(0)
}
class stdClass#1 (1) {
  public $num =>
  int(1)
}
class stdClass#1 (1) {
  public $num =>
  int(2)
}
class stdClass#1 (1) {
  public $num =>
  int(3)
}
class stdClass#1 (1) {
  public $num =>
  int(4)
}

有人可以向我解释为什么循环中的var_dump能够打印出不同的对象属性，但是当它被推入数组时，object属性会成为最后一个值吗？

是因为我在推动同一个物体吗？在重新分配期间如何处理变量但不处理对象？

Answer 1

每次都在数组中放置相同的对象：

// instance of the object
$test_obj = new stdClass(); 
$array = [];
for ($i=0; $i < 5; $i++) { 
    $test_obj->num = $i;
    array_push($array, $test_obj);
}

与做：

相同

$test_obj = new stdClass(); 
$array = [$test_obj, $test_obj, $test_obj, $test_obj, $test_obj];

因此，如果更改对象的某些属性，它将对所有数组项执行此操作，因为它们引用相同的对象：

$test_obj = new stdClass(); 
$test_obj->num = 0;
// all items in the array now are `0`
$array = [$test_obj, $test_obj, $test_obj, $test_obj, $test_obj];
$test_obj->num = 1;
// all items in the array now are `1`

它适用于您的第二个示例的原因是因为您正在创建一个新对象并将其附加到数组。

你的第三个例子做它所做的事情的原因是因为那时是对象的值：

$test_obj = new stdClass(); 
$test_obj->num = 0;
var_dump($test_obj); // ->num == 0
$test_obj->num = 1;
var_dump($test_obj); // ->num == 1
$test_obj->num = 2;
var_dump($test_obj); // ->num == 2

$test_obj = new stdClass(); 
$array = [];
for ($i=0; $i < 5; $i++) { 
    $test_obj->num = $i;
    array_push($array, $test_obj);
    // $test_obj->num == 0 on first iteration
    // $test_obj->num == 1 on first iteration
    // $test_obj->num == 3 on first iteration
    // $test_obj->num == 4 on first iteration
}

// $test_obj->num == 4 after the loop finished which is the same as your first example

循环中的对象属性重新分配

1 个答案: