PHP中的数组

数组用途

• array
• list/vector
• hash table
• dictionary
• collection
• queue
• stack
• tree
• multidimensional array

---

PHP数组本质

• hash table

---

数组定义

• 注意
  
  • The comma after the last array element is optional and can be omitted.格式约束
  • As of PHP 5.4 you can also use the short array syntax, which replaces array() with [].格式约束
  • The key can either be an integer or a string. The value can be of any type. key如果采用别的类型的话会发生类型转换或报warning，避免这种情况出现
  • If multiple elements in the array declaration use the same key, only the last one will be used as all others are overwritten.数据覆盖
  • PHP arrays can contain integer and string keys at the same time as PHP does not distinguish between indexed and associative arrays.key 类型是可以混合使用的
  • The key is optional. If it is not specified, PHP will use the increment of the largest previously used integer key.key的值是默认以最大一个有效int类型的key标准增加的

-

# array
    $array = ("Monday",
    "Tursday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday",
    "Sunday",);
# dictionary
    $person = array(
        "id" => 12345,
        "name" => "chenxilin",
        "age" => 25,);

---

数组引用

• [key] 或 {key} 多维数组可多个
• As of PHP 5.4 it is possible to array dereference the result of a function or method call directly.
• As of PHP 5.5 it is possible to array dereference an array literal.
• 注意：
  
  • 特殊赋值：arr[] = value，用于追加value值到数组中，key采用数组中最大一个有效int类型的key增加；
  • 如果该数组arr不存在或原来不是数组时，这会被创建一个新的数组出来并添加元素。

---

数组修改、删除

• To change a certain value, assign a new value to that element using its key. To remove a key/value pair, call the unset() function on it.使用unset方法，可以删除整个数组或其中某个key/value

---

数组遍历

foreach ($arr as $key => $value ) {
    // do something for $key and $value;
}

---

有用的方法

• array_value($arr) 返回一个re-index的数组，使得key中int类型是从0开始连续增长的而不会断开。
• count($arr) 获得数组长度
• sort($arr) … 数组排序算法

---

迭代器接口实现foreach

实现构造方法和以下接口
1. Iterator::current — Return the current element
2. Iterator::key — Return the key of the current element
3. Iterator::next — Move forward to next element
4. Iterator::rewind — Rewind the Iterator to the first element
5. Iterator::valid — Checks if current position is valid