PHP中的數組

數組用途

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

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PHP數組本質

• hash table

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數組定義

• 注意
  
  • The comma after the last array element is optional and can be omitted.格式約束
  • As of PHP 5.4 you can also use the short array syntax, which replaces array() with [].格式約束
  • The key can either be an integer or a string. The value can be of any type. key如果採用別的類型的話會發生類型轉換或報warning，避免這種情況出現
  • If multiple elements in the array declaration use the same key, only the last one will be used as all others are overwritten.數據覆蓋
  • PHP arrays can contain integer and string keys at the same time as PHP does not distinguish between indexed and associative arrays.key 類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的值是默認以最大一個有效int類型的key標準增加的

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

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數組引用

• [key] 或 {key} 多維數組可多個
• 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：
  
  • 特殊賦值：arr[] = value，用於追加value值到數組中，key採用數組中最大一個有效int類型的key增加；
  • 如果該數組arr不存在或原來不是數組時，這會被創建一個新的數組出來並添加元素。

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數組修改、刪除

• 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，可以刪除整個數組或其中某個key/value

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數組遍歷

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

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有用的方法

• array_value($arr) 返回一個re-index的數組，使得key中int類型是從0開始連續增長的而不會斷開。
• count($arr) 獲得數組長度
• sort($arr) … 數組排序算法

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迭代器接口實現foreach

實現構造方法和以下接口
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