如何在 PHP 中创建一个预定义大小的空数组？

How to create an empty array in PHP with predefined size?

提问by Reed Richards

I am creating a new array in a for loop.

我正在 for 循环中创建一个新数组。

for $i < $number_of_items
    $data[$i] = $some_data;

PHP keeps complaining about the offset since for each iteration I add a new index for the array, which is kind of stupid.

PHP 一直抱怨偏移量，因为每次迭代我都会为数组添加一个新索引，这有点愚蠢。

Notice: Undefined offset: 1 in include() (line 23 of /...
Notice: Undefined offset: 1 in include() (line 23 of /..
Notice: Undefined offset: 1 in include() (line 23 of /..

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Is there some way to predefine the number items in the array so that PHP will not show this notice?

有没有办法预先定义数组中的数字项，这样PHP就不会显示这个通知？

In other words, can I predefine the size of the array in a similar way to this?

换句话说，我可以以与此类似的方式预定义数组的大小吗？

$myarray = array($size_of_the_earray);

回答by Jon

There is no way to create an array of a predefined size without also supplying values for the elements of that array.

如果不为该数组的元素提供值，就无法创建一个预定义大小的数组。

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The best way to initialize an array like that is array_fill. By far preferable over the various loop-and-insert solutions.

像这样初始化数组的最佳方法是array_fill. 远远优于各种循环和插入解决方案。

$my_array = array_fill(0, $size_of_the_array, $some_data);

Every position in the $my_arraywill contain $some_data.

中的每个位置都$my_array将包含$some_data.

The first zero in array_filljust indicates the index from where the array needs to be filled with the value.

中的第一个零array_fill仅表示需要用值填充数组的索引。

回答by Jean-Philippe Leclerc

You can't predefine a size of an array in php. A good way to acheive your goal is the following:

您不能在 php 中预定义数组的大小。实现目标的一个好方法是：

// Create a new array.
$array = array(); 

// Add an item while $i < yourWantedItemQuantity
for ($i = 0; $i < $number_of_items; $i++)
{
    array_push($array, $some_data);
    //or $array[] = $some_data; for single items.
}

Note that it is way faster to use array_fill() to fill an Array :

请注意，使用 array_fill() 填充 Array 会更快：

$array = array_fill(0,$number_of_items, $some_data);

If you want to verify if a value has been set at an index, you should use the following: array_key_exists("key", $array) or isset($array["key"])

如果要验证是否已在索引处设置值，应使用以下命令：array_key_exists("key", $array) 或 isset($array["key"])

See array_key_exists, issetand array_fill

参见array_key_exists、 isset和 array_fill

回答by Madbreaks

Possibly related, if you want to initialize and fill an array with a range of values, use PHP's (wait for it...) range function:

可能相关，如果你想用一系列值初始化和填充数组，请使用 PHP 的（等待它......）范围函数：

$a = range(1, 5);  // array(1,2,3,4,5)
$a = range(0, 10, 2); // array(0,2,4,6,8,10)

回答by Jacob

PHP Arraysdon't need to be declared with a size.

PHP 数组不需要声明大小。

An array in PHP is actually an ordered map

PHP 中的数组实际上是一个有序映射

You also shouldn't get a warning/notice using code like the example you have shown. The common Notice people get is "Undefined offset" when reading from an array.

您也不应该使用像您显示的示例那样的代码收到警告/通知。从数组中读取时，人们得到的常见通知是“未定义的偏移量”。

A way to counter this is to check with issetor array_key_exists, or to use a function such as:

解决此问题的一种方法是使用isset或检查array_key_exists，或使用以下函数：

function isset_or($array, $key, $default = NULL) {
    return isset($array[$key]) ? $array[$key] : $default;
}

So that you can avoid the repeated code.

这样就可以避免重复的代码。

Note: issetreturns false if the element in the array is NULL, but has a performance gain over array_key_exists.

注意：isset如果数组中的元素为 NULL，则返回 false，但性能提升超过array_key_exists.

If you want to specify an array with a size for performance reasons, look at:

如果出于性能原因要指定具有大小的数组，请查看：

SplFixedArrayin the Standard PHP Library.

标准 PHP 库中的SplFixedArray。

回答by Academia

There is also array_pad. You can use it like this:

还有array_pad。你可以这样使用它：

$data = array_pad($data,$number_of_items,0);

For initializing with zeros the $number_of_items positions of the array $data.

用零初始化数组 $data 的 $number_of_items 位置。

回答by Chandan Sharma

PHP provides two types of array.

PHP 提供了两种类型的数组。

• normal array
• SplFixedArray

• 普通数组
• 固定数组

normal array : This array is dynamic.

普通数组：这个数组是动态的。

SplFixedArray : this is a standard php library which provides the ability to create array of fix size.

SplFixedArray ：这是一个标准的 php 库，它提供了创建固定大小数组的能力。

回答by user10620381

 $array = new SplFixedArray(5);
   echo $array->getSize()."\n";

You can use PHP documentation more info check this link https://www.php.net/manual/en/splfixedarray.setsize.php

您可以使用 PHP 文档了解更多信息，请查看此链接 https://www.php.net/manual/en/splfixedarray.setsize.php