PHP中的Array-php手册-php.cn

PHP中的数组是一个有序映射(1对1的关系 key-value)。 Array是一个综合体：可表示数组、字典、集合等。 key可以是int或string。value可以是任意类型。 key如下情况会强制转换： 1.包含合法整型值的字符串=整型。 "8"=8 实际存储8 2.浮点数=整型。 8.7=8 小数

PHP中的数组是一个有序映射(1对1的关系 key->value)。
Array是一个综合体：可表示数组、字典、集合等。

key可以是int或string。value可以是任意类型。

key如下情况会强制转换：
1.包含合法整型值的字符串=>整型。 "8"=>8 实际存储8
2.浮点数=>整型。 8.7=>8 小数点会被舍去
3.布尔类型=>类型。 true=>1,false=>0 实际存储为0或1
4.Null=>“” 实际存储""
5.数组和对象不能被用为键名。

键名不可重复，若重复，则只有最后一个有效。

<span>php
</span><span>$array</span> = <span>array</span><span>(
    </span>1    => "a",
    "1"  => "b",
    1.5  => "c",
    <span>true</span> => "d",<span>
);
</span><span>var_dump</span>(<span>$array</span><span>);
</span>?>

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以上例程会输出：

<span>array</span>(1<span>) {
  [</span>1]=>
  <span>string</span>(1) "d"<span>
}</span>

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上例中所有的键名都被强制转换为 1，则每一个新单元都会覆盖前一个的值，最后剩下的只有一个 "d"。

PHP数组可以同时含有int和string类型的键名，因为PHP 实际并不区分索引数组和关联数组。

如果对给出的值没有指定键名，则取当前最大的整数索引值，而新的键名将是该值加一。如果指定的键名已经有了值，则该值会被覆盖。

Example #5 仅对部分单元指定键名

<span>php
</span><span>$array</span> = <span>array</span><span>(
         </span>"a",
         "b",
    6 => "c",
         "d",<span>
);
</span><span>var_dump</span>(<span>$array</span><span>);
</span>?>

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以上例程会输出：

<span>array</span>(4<span>) {
  [</span>0]=>  //默认从0开始
  <span>string</span>(1) "a"<span>
  [</span>1]=>
  <span>string</span>(1) "b"<span>
  [</span>6]=>
  <span>string</span>(1) "c"<span>
  [</span>7]=>   //没指定键，则从上个索引值+1
  <span>string</span>(1) "d"<span>
}</span>

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数组单元可以通过 array[key] 语法来访问。
Example #6 访问数组单元

<span>php
</span><span>$array</span> = <span>array</span><span>(
    </span>"foo" => "bar",
    42    => 24,
    "multi" => <span>array</span><span>(
         </span>"dimensional" => <span>array</span><span>(
             </span>"array" => "foo"<span>
         )
    )
);

</span><span>var_dump</span>(<span>$array</span>["foo"<span>]);
</span><span>var_dump</span>(<span>$array</span>[42<span>]);
</span><span>var_dump</span>(<span>$array</span>["multi"]["dimensional"]["array"<span>]);
</span>?>

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以上例程会输出：

<span>string</span>(3) "bar"<span>
int(</span>24<span>)
</span><span>string</span>(3) "foo"

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Note:

方括号和花括号可以互换使用来访问数组单元（例如 $array[42] 和 $array{42} 在上例中效果相同）。

要修改某个值，通过其键名给该单元赋一个新值。要删除某键值对，对其调用 unset() 函数。

<span>php
</span><span>$arr</span> = <span>array</span>(5 => 1, 12 => 2<span>);

</span><span>$arr</span>[] = 56;    <span>//</span><span> This is the same as $arr[13] = 56;
                // at this point of the script</span>

<span>$arr</span>["x"] = 42; <span>//</span><span> This adds a new element to
                // the array with key "x"</span>
                
<span>unset</span>(<span>$arr</span>[5]); <span>//</span><span> This removes the element from the array</span>

<span>unset</span>(<span>$arr</span>);    <span>//</span><span> This deletes the whole array</span>
?>

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Note:<span>

如上所述，如果给出方括号但没有指定键名，则取当前最大整数索引值，新的键名将是该值加上 </span>1（但是最小为 0）。如果当前还没有整数索引，则键名将为 0<span>。

注意这里所使用的最大整数键名不一定当前就在数组中。它只要在上次数组重新生成索引后曾经存在过就行了。以下面的例子来说明：</span>

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<span>php
</span><span>//</span><span> 创建一个简单的数组</span>
<span>$array</span> = <span>array</span>(1, 2, 3, 4, 5<span>);
</span><span>print_r</span>(<span>$array</span><span>);

</span><span>//</span><span> 现在删除其中的所有元素，但保持数组本身不变:</span>
<span>foreach</span> (<span>$array</span> <span>as</span> <span>$i</span> => <span>$value</span><span>) {
    </span><span>unset</span>(<span>$array</span>[<span>$i</span><span>]);
}
</span><span>print_r</span>(<span>$array</span><span>);

</span><span>//</span><span> 添加一个单元（注意新的键名是 5，而不是你可能以为的 0）</span>
<span>$array</span>[] = 6<span>;
</span><span>print_r</span>(<span>$array</span><span>);

</span><span>//</span><span> 重新索引：</span>
<span>$array</span> = <span>array_values</span>(<span>$array</span><span>);
</span><span>$array</span>[] = 7<span>;
</span><span>print_r</span>(<span>$array</span><span>);
</span>?>

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以上例程会输出：

<span>Array</span><span>
(
    [</span>0] => 1<span>
    [</span>1] => 2<span>
    [</span>2] => 3<span>
    [</span>3] => 4<span>
    [</span>4] => 5<span>
)
</span><span>Array</span><span>
(
)
</span><span>Array</span><span>
(
    [</span>5] => 6<span>
)
</span><span>Array</span><span>
(
    [</span>0] => 6<span>
    [</span>1] => 7<span>
)</span>

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转换为数组

对于任意 integer，float，string，boolean 和 resource 类型，如果将一个值转换为数组，将得到一个仅有一个元素的数组，其下标为 0，该元素即为此标量的值。换句话说，(array)$scalarValue 与 array($scalarValue) 完全一样。

如果一个 object 类型转换为 array，则结果为一个数组，其单元为该对象的属性。键名将为成员变量名，不过有几点例外：整数属性不可访问；私有变量前会加上类名作前缀；保护变量前会加上一个 '*' 做前缀。这些前缀的前后都各有一个 NULL 字符。这会导致一些不可预知的行为：

<span>php

</span><span>class</span><span> A {
    </span><span>private</span> <span>$A</span>; <span>//</span><span> This will become '\0A\0A'</span>
<span>}

</span><span>class</span> B <span>extends</span><span> A {
    </span><span>private</span> <span>$A</span>; <span>//</span><span> This will become '\0B\0A'</span>
    <span>public</span> <span>$AA</span>; <span>//</span><span> This will become 'AA'</span>
<span>}

</span><span>var_dump</span>((<span>array</span>) <span>new</span><span> B());
</span>?>

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上例会有两个键名为 'AA'，不过其中一个实际上是 '\0A\0A'。

将 NULL 转换为 array 会得到一个空的数组。

多用途的数组类型Array，以下为示例：

Example #8 使用 array()

<span>php
</span><span>//</span><span> Array as (property-)map</span>
<span>$map</span> = <span>array</span>( 'version'    => 4,
              'OS'         => 'Linux',
              'lang'       => 'english',
              'short_tags' => <span>true</span><span>
            );
            
</span><span>//</span><span> strictly numerical keys</span>
<span>$array</span> = <span>array</span>( 7,
                8,
                0,
                156,
                -10<span>
              );
</span><span>//</span><span> this is the same as array(0 => 7, 1 => 8, ...)</span>

<span>$switching</span> = <span>array</span>(         10, <span>//</span><span> key = 0</span>
                    5    =>  6,
                    3    =>  7, 
                    'a'  =>  4,
                            11, <span>//</span><span> key = 6 (maximum of integer-indices was 5)</span>
                    '8'  =>  2, <span>//</span><span> key = 8 (integer!)</span>
                    '02' => 77, <span>//</span><span> key = '02'</span>
                    0    => 12  <span>//</span><span> the value 10 will be overwritten by 12</span>
<span>                  );
                  
</span><span>//</span><span> empty array</span>
<span>$empty</span> = <span>array</span><span>();         
</span>?>

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Example #9 集合

<span>php
</span><span>$colors</span> = <span>array</span>('red', 'blue', 'green', 'yellow'<span>);

</span><span>foreach</span> (<span>$colors</span> <span>as</span> <span>$color</span><span>) {
    </span><span>echo</span> "Do you like <span>$color</span>?\n"<span>;
}
</span>?>

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以上例程会输出：

<span>Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?</span>

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Example #10 在循环中改变单元

<span>php
</span><span>//</span><span> PHP 5</span>
<span>foreach</span> (<span>$colors</span> <span>as</span> &<span>$color</span><span>) {
    </span><span>$color</span> = <span>strtoupper</span>(<span>$color</span><span>);
}
</span><span>unset</span>(<span>$color</span>); <span>/*</span><span> ensure that following writes to
$color will not modify the last array element </span><span>*/</span>

<span>//</span><span> Workaround for older versions</span>
<span>foreach</span> (<span>$colors</span> <span>as</span> <span>$key</span> => <span>$color</span><span>) {
    </span><span>$colors</span>[<span>$key</span>] = <span>strtoupper</span>(<span>$color</span><span>);
}

</span><span>print_r</span>(<span>$colors</span><span>);
</span>?>

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以上例程会输出：

<span>Array
(
    [0] => RED
    [1] => BLUE
    [2] => GREEN
    [3] => YELLOW
)</span>

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Example #14 递归和多维数组

<span>php
</span><span>$fruits</span> = <span>array</span> ( "fruits"  => <span>array</span> ( "a" => "orange",
                                       "b" => "banana",
                                       "c" => "apple"<span>
                                     )</span>,
                  "numbers" => <span>array</span> ( 1,
                                       2,
                                       3,
                                       4,
                                       5,
                                       6<span>
                                     )</span>,
                  "holes"   => <span>array</span> (      "first",
                                       5 => "second",
                                            "third"<span>
                                     )
                );

</span><span>//</span><span> Some examples to address values in the array above </span>
<span>echo</span> <span>$fruits</span>["holes"][5];    <span>//</span><span> prints "second"</span>
<span>echo</span> <span>$fruits</span>["fruits"]["a"]; <span>//</span><span> prints "orange"</span>
<span>unset</span>(<span>$fruits</span>["holes"][0]);  <span>//</span><span> remove "first"

// Create a new multi-dimensional array</span>
<span>$juices</span>["apple"]["green"] = "good"<span>; 
</span>?><span>

数组(</span><span>Array</span><span>) 的赋值总是会涉及到值的拷贝。使用引用运算符通过引用来拷贝数组。
</span><span>php
</span><span>$arr1</span> = <span>array</span>(2, 3<span>);
</span><span>$arr2</span> = <span>$arr1</span><span>;
</span><span>$arr2</span>[] = 4; <span>//</span><span> $arr2 is changed,
             // $arr1 is still array(2, 3)</span>
             
<span>$arr3</span> = &<span>$arr1</span><span>;
</span><span>$arr3</span>[] = 4; <span>//</span><span> now $arr1 and $arr3 are the same</span>
?>

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