PHP | foreach 循环

在 PHP 中，foreach 循环被用来遍历数组和对象。它的语法如下：

foreach ($array as $value) {
  // 代码块
}
// 或者
foreach ($array as $key => $value) {
  // 代码块
}

其中，$array 是要遍历的数组或对象的名称；$value 是每次循环中当前的值，如果使用第二种语法，则还可以用 $key 来获取当前的键名。

以下是一个简单的例子，遍历数组并输出每个元素：

$fruits = array("apple", "banana", "orange");
foreach ($fruits as $fruit) {
  echo $fruit . "<br>";
}
// 输出结果：apple banana orange

当然，foreach 循环还支持break、continue语句和多层嵌套。

示例

以下是一个更复杂的示例——使用 foreach 循环遍历多维数组和对象：

$students = array(
  array("name" => "Alice", "age" => 21, "gender" => "female"),
  array("name" => "Bob", "age" => 22, "gender" => "male"),
  array("name" => "Charlie", "age" => 23, "gender" => "male")
);

foreach ($students as $student) {
  foreach ($student as $key => $value) {
    echo $key . ": " . $value . ", ";
  }
  echo "<br>";
}
// 输出结果：name: Alice, age: 21, gender: female; name: Bob, age: 22, gender: male; name: Charlie, age: 23, gender: male;

同样的操作可以用来遍历对象。例如：

class Student {
  public $name;
  public $age;
  public $gender;
  function __construct($name, $age, $gender) {
    $this->name = $name;
    $this->age = $age;
    $this->gender = $gender;
  }
}

$students = array(
  new Student("Alice", 21, "female"),
  new Student("Bob", 22, "male"),
  new Student("Charlie", 23, "male")
);

foreach ($students as $student) {
  foreach ($student as $key => $value) {
    echo $key . ": " . $value . ", ";
  }
  echo "<br>";
}
// 输出结果：name: Alice, age: 21, gender: female; name: Bob, age: 22, gender: male; name: Charlie, age: 23, gender: male;

小结

PHP 中的 foreach 循环是一个非常有用的工具，可以轻松遍历数组和对象。通过灵活使用它，可以轻松地处理许多常见的编程任务。