什么是“索引超出范围"?异常,我该如何解决? [英] What is an "index out of range" exception, and how do I fix it?
问题描述
我收到以下错误之一:
- 索引超出范围.必须为非负且小于集合的大小"
- 插入索引超出范围.必须为非负且小于或等于大小."
- 索引超出数组范围."
这是什么意思,我该如何解决?
What does it mean, and how do I fix it?
另见
IndexOutOfRangeException
ArgumentOutOfRangeException
推荐答案
为什么会出现这个错误?
因为您尝试使用超出集合边界的数字索引访问集合中的元素.
Why does this error occur?
Because you tried to access an element in a collection, using a numeric index that exceeds the collection's boundaries.
集合中的第一个元素通常位于索引 0
.最后一个元素位于索引 n-1
处,其中 n
是集合的 Size
(它包含的元素数).如果您尝试使用负数作为索引,或者使用大于 Size-1
的数字,则会出现错误.
The first element in a collection is generally located at index 0
. The last element is at index n-1
, where n
is the Size
of the collection (the number of elements it contains). If you attempt to use a negative number as an index, or a number that is larger than Size-1
, you're going to get an error.
当你像这样声明一个数组时:
When you declare an array like this:
var array = new int[6]
数组中的第一个和最后一个元素是
The first and last elements in the array are
var firstElement = array[0];
var lastElement = array[5];
所以当你写:
var element = array[5];
您正在检索数组中的第六个元素,而不是第五个.
you are retrieving the sixth element in the array, not the fifth one.
通常,你会像这样循环遍历一个数组:
Typically, you would loop over an array like this:
for (int index = 0; index < array.Length; index++)
{
Console.WriteLine(array[index]);
}
这是可行的,因为循环从零开始,到 Length-1
结束,因为 index
不再小于 Length
.
This works, because the loop starts at zero, and ends at Length-1
because index
is no longer less than Length
.
然而,这将引发异常:
for (int index = 0; index <= array.Length; index++)
{
Console.WriteLine(array[index]);
}
注意到 <=
了吗?index
现在将在最后一次循环迭代中超出范围,因为循环认为 Length
是有效索引,但事实并非如此.
Notice the <=
there? index
will now be out of range in the last loop iteration, because the loop thinks that Length
is a valid index, but it is not.
列表的工作方式相同,不同之处在于您通常使用 Count
而不是 Length
.它们仍然从零开始,到 Count - 1
结束.
Lists work the same way, except that you generally use Count
instead of Length
. They still start at zero, and end at Count - 1
.
for (int index = 0; i < list.Count; index++)
{
Console.WriteLine(list[index]);
}
但是,您也可以使用 foreach
遍历列表,从而完全避免索引的整个问题:
However, you can also iterate through a list using foreach
, avoiding the whole problem of indexing entirely:
foreach (var element in list)
{
Console.WriteLine(element.ToString());
}
您不能索引尚未添加到集合中的元素.
You cannot index an element that hasn't been added to a collection yet.
var list = new List<string>();
list.Add("Zero");
list.Add("One");
list.Add("Two");
Console.WriteLine(list[3]); // Throws exception.
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