php current() 方法
时间: 2024-03-12 21:47:35 浏览: 13
`current()` 方法是 PHP 内置函数之一,用于返回数组或对象中当前指针所指向的元素的值。具体来说,`current()` 方法的作用是返回数组或对象当前指针所指向的元素的值,并将指针向后移动一位。如果当前指针所指向的元素不存在,则返回 false。
以下是一个示例数组和使用 `current()` 方法的示例代码:
```php
$arr = array('a', 'b', 'c', 'd');
echo current($arr); // 输出 a
```
在上面的示例中,首先定义了一个包含四个元素的数组 `$arr`,然后使用 `current()` 方法获取数组的第一个元素,即 `'a'`,并将其输出到屏幕上。
需要注意的是,如果在使用 `current()` 方法之前没有调用 `reset()` 方法对数组或对象的指针进行重置,那么 `current()` 方法将从数组或对象的当前指针位置开始遍历。因此,在使用 `current()` 方法之前,通常需要先使用 `reset()` 方法将指针重置到数组或对象的第一个元素。
相关问题
php 二叉树
以下是 PHP 实现二叉树的基本代码:
```
class TreeNode {
public $value;
public $left;
public $right;
public function __construct($val) {
$this->value = $val;
$this->left = null;
$this->right = null;
}
}
class BinaryTree {
public $root;
public function __construct() {
$this->root = null;
}
public function insert($val) {
$new_node = new TreeNode($val);
if ($this->root == null) {
$this->root = $new_node;
return;
}
$current = $this->root;
while (true) {
if ($val < $current->value) {
if ($current->left == null) {
$current->left = $new_node;
return;
} else {
$current = $current->left;
}
} else {
if ($current->right == null) {
$current->right = $new_node;
return;
} else {
$current = $current->right;
}
}
}
}
public function search($val) {
$current = $this->root;
while ($current != null) {
if ($val == $current->value) {
return $current;
} elseif ($val < $current->value) {
$current = $current->left;
} else {
$current = $current->right;
}
}
return null;
}
public function delete($val) {
$parent = null;
$current = $this->root;
$is_left_child = false;
while ($current != null) {
if ($val == $current->value) {
if ($current->left == null && $current->right == null) {
if ($current == $this->root) {
$this->root = null;
} elseif ($is_left_child) {
$parent->left = null;
} else {
$parent->right = null;
}
} elseif ($current->left == null) {
if ($current == $this->root) {
$this->root = $current->right;
} elseif ($is_left_child) {
$parent->left = $current->right;
} else {
$parent->right = $current->right;
}
} elseif ($current->right == null) {
if ($current == $this->root) {
$this->root = $current->left;
} elseif ($is_left_child) {
$parent->left = $current->left;
} else {
$parent->right = $current->left;
}
} else {
$successor = $this->get_successor($current);
if ($current == $this->root) {
$this->root = $successor;
} elseif ($is_left_child) {
$parent->left = $successor;
} else {
$parent->right = $successor;
}
$successor->left = $current->left;
}
return;
} elseif ($val < $current->value) {
$parent = $current;
$current = $current->left;
$is_left_child = true;
} else {
$parent = $current;
$current = $current->right;
$is_left_child = false;
}
}
}
public function get_successor($del_node) {
$successor_parent = $del_node;
$successor = $del_node;
$current = $del_node->right;
while ($current != null) {
$successor_parent = $successor;
$successor = $current;
$current = $current->left;
}
if ($successor != $del_node->right) {
$successor_parent->left = $successor->right;
$successor->right = $del_node->right;
}
return $successor;
}
}
// 示例用法
$tree = new BinaryTree();
$tree->insert(5);
$tree->insert(3);
$tree->insert(7);
$tree->insert(1);
$tree->insert(4);
$tree->insert(6);
$tree->insert(8);
print_r($tree->search(5)); // 输出: TreeNode Object ( [value] => 5 [left] => TreeNode Object ( [value] => 3 [left] => TreeNode Object ( [value] => 1 [left] => [right] => ) [right] => TreeNode Object ( [value] => 4 [left] => [right] => ) ) [right] => TreeNode Object ( [value] => 7 [left] => TreeNode Object ( [value] => 6 [left] => [right] => ) [right] => TreeNode Object ( [value] => 8 [left] => [right] => ) ) )
$tree->delete(4);
print_r($tree->search(4)); // 输出: null
```
上面的代码实现了二叉树的基本功能,包括插入节点、查找节点和删除节点。在实际使用时,可根据需要进行修改和扩展。
Php的mysql建表
在PHP中,可以使用MySQLi和PDO两种方式来连接MySQL数据库。以下是使用MySQLi方式创建MySQL数据表的示例代码:
```php
<?php
// 连接MySQL数据库
$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "myDB";
$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
// 创建数据表
$sql = "CREATE TABLE MyGuests (
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
firstname VARCHAR(30) NOT NULL,
lastname VARCHAR(30) NOT NULL,
email VARCHAR(50),
reg_date TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
)";
if ($conn->query($sql) === TRUE) {
echo "数据表创建成功";
} else {
echo "数据表创建失败: " . $conn->error;
}
$conn->close();
?>
```
以上代码创建了一个名为MyGuests的数据表,其中包含id、firstname、lastname、email和reg_date五个字段。其中id为自动递增主键,firstname和lastname为非空字段,email为可选字段,reg_date为TIMESTAMP类型的默认值为当前时间的字段。