无法在foreach中向数组添加新字段

Question

我有一个二维数组:

$test = array(
    "foo" => array(
        'a' => 1,
        'b' => 2,
        'c' => 3
    ),
    "bar" => array(
        'a' => 1,
        'b' => 2,
        'c' => 3
    ),
    "baz" => array(
        'a' => 1,
        'b' => 2,
        'c' => 3
    )
);

我想添加一个以'd'值命名的字段4到外部数组的每个元素,以便生成的数组变为:

array(
    "foo" => array(
        'a' => 1,
        'b' => 2,
        'c' => 3,
        'd' => 4
    ),
    "bar" => array(
        'a' => 1,
        'b' => 2,
        'c' => 3,
        'd' => 4
    ),
    "baz" => array(
        'a' => 1,
        'b' => 2,
        'c' => 3,
        'd' => 4
    )
)

我试过这个:

foreach ( $test as $elem ) 
{
    $elem['d'] = 4;
}

这不起作用.我做错了什么,我怎样才能做到这一点？

Answer 1

数组中传递的数组和基元(尽管对象是通过引用传递的).在foreach循环中克服此问题的一种方法是通过循环中的引用访问子数组:

// Call $elem by reference with &
foreach ( $test as &$elem ) {
    $elem['d'] = 4;
}

print_r($test);
array(3) {
  ["foo"]=>
  array(4) {
    ["a"]=>
    int(1)
    ["b"]=>
    int(2)
    ["c"]=>
    int(3)
    ["d"]=>
    int(4)
  }
  ...
}