为什么 `new int[x]{}` 无效？

发布于 2024-09-02 09:30:55 字数 463 浏览 6 评论 0原文

在 MonoDevelop 中，我有以下可以编译的代码：

int[] row = new int[indices.Count]{};

但是，在运行时，我得到：

Matrix.cs(53,53)：错误 CS0150：A 预期值恒定 (CS0150) （测试矩阵）

我知道这个错误意味着什么，并迫使我调整数组大小：

int[] row = new int[indices.Count]{};
Array.Resize(ref row, rowWidth);

这是我必须处理的事情吗，因为我在 Linux 上使用 MonoDevelop？我确信在 .Net 3.5 下我能够使用包含数组宽度的变量来初始化数组。谁能确认这是孤立的吗？如果是这样，我可以向 bugzilla 报告该错误。

原文

In MonoDevelop I have the following code which compiles:

int[] row = new int[indices.Count]{};

However, at run-time, I get:

Matrix.cs(53,53): Error CS0150: A
constant value is expected (CS0150)
(testMatrix)

I know what this error means and forces me to then resize the array:

int[] row = new int[indices.Count]{};
Array.Resize(ref row, rowWidth);

Is this something I just have to deal with because I am using MonoDevelop on Linux? I was certain that under .Net 3.5 I was able to initialize an array with a variable containing the width of the array. Can anyone confirm that this is isolated? If so, I can report the bug to bugzilla.

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审判长 2024-09-09 09:30:56

不能将数组创建语法与对象初始化语法混合在一起。删除 { }.

当您编写时：

int[] row = new int[indices.Count];

您正在创建一个大小为 indices.Count 并初始化为默认值的新数组。

当您编写时：

int[] row = new int[] { 1, 2, 3, 4 };

您正在创建一个数组，然后将其内容初始化为值 [1,2,3,4]。数组的大小是根据元素的数量推断的。它的简写是：

int[] row = new int[4];
row[0] = 1;
row[1] = 2;
row[2] = 3;
row[3] = 4;

数组仍然首先初始化为默认值，这种语法只是提供了一种简写，以避免必须自己编写这些额外的赋值。

You can't mix array creation syntax with object initialization syntax. Remove the { }.

When you write:

int[] row = new int[indices.Count];

You are creating a new array of size indices.Count initialized to default values.

When you write:

int[] row = new int[] { 1, 2, 3, 4 };

You are creating an array and then initializing it's content to the values [1,2,3,4]. The size of the array is inferred from the number of elements. It's shorthand for:

int[] row = new int[4];
row[0] = 1;
row[1] = 2;
row[2] = 3;
row[3] = 4;

The array is still first initialized to defaults, this syntax just provides a shorthand to avoid havind to write those extra assignments yourself.

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写下不归期 2024-09-09 09:30:56

以下代码由于同样的原因在 Windows/.NET/LINQPad 上无法编译：

void Main()
{
    int[] row = new int[indices.Count]{};
    row[2] = 10;
    row.Dump();
}

// Define other methods and classes here
public class indices {
    public static int Count = 5;
}

但是，从声明中删除对象初始化 ({}) 使其可以工作。

The following code fails to compile for the same reason on Windows/.NET/LINQPad:

void Main()
{
    int[] row = new int[indices.Count]{};
    row[2] = 10;
    row.Dump();
}

// Define other methods and classes here
public class indices {
    public static int Count = 5;
}

However, removing the object initialisation from the declaration ({}) makes it work.

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多像笑话 2024-09-09 09:30:56

在 C# 中，如果要声明空数组，语法应为：

int[] row = new int[indices.Count];

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我不在是我 2024-09-09 09:30:56

因为当您使用数组初始化语法并指定数组的大小时，

int[] arr = new int[5]{1,2,3,4,5};

数组的大小是多余的信息。编译器可以从初始化列表推断大小。正如其他人所说，您可以创建空数组：

int[] arr = new int[5];

或使用初始化列表：

int[] arr = {1,2,3,4,5};

Because when you to use use array initialization syntax AND specify the size of the array

int[] arr = new int[5]{1,2,3,4,5};

The size of the array is superfluous information. The compiler can infer the size from the initialization list. As others have said, you either create empty array: