C＃中子字符串的异常行为 [英] Unexpected behavior of Substring in C#

问题描述

.net System.String 类中 Substring（）方法的定义就像这样

The definition of Substring() method in .net System.String class is like this

public string Substring(int startIndex)

其中 startIndex 是根据该方法定义，此实例中子字符串的从零开始的字符位置 。如果我正确理解它，则意味着它将给我一部分字符串，从给定的从零开始的索引开始。

Where startIndex is "The zero-based starting character position of a substring in this instance" as per the method definition. If i understand it correctly, it means it will give me a part of the string, starting at the given zero-based index.

现在，如果我有一个字符串 ABC 并使用具有不同索引的子字符串，我得到以下结果。

Now, if I have a string "ABC" and take substring with different indexes, I get following results.

var str = "ABC";
var chars = str.ToArray(); //returns 3 char 'A', 'B', 'C' as expected

var sub2 = str.Substring(2); //[1] returns "C" as expected
var sub3 = str.Substring(3); //[2] returns "" ...!!! Why no exception??
var sub4 = str.Substring(4); //[3] throws ArgumentOutOfRangeException as expected

为什么不为案例[2]抛出异常??

Why it doesn't throw exception for case [2] ??

该字符串具有3个字符，因此索引为 [0，1，2] 甚至 ToArray（）， ToCharArray（）方法将按预期返回3个字符！如果我尝试使用起始索引为 3 的 Substring（）抛出异常？

The string has 3 characters, so indexes are [0, 1, 2], and even ToArray(), ToCharArray() method returns 3 characters as expected! Shouldn't it throw exception if I try to Substring() with starting index 3?

推荐答案

文档非常明确地表明这是正确的行为：

The documentation is quite explicit about this being correct behaviour:

返回值：一个等效于字符串的字符串在这种情况下以startIndex开头的子字符串；如果startIndex等于该实例的长度，则为 Empty。

Return value: a string that is equivalent to the substring that begins at startIndex in this instance, or Empty if startIndex is equal to the length of this instance.

如果 startIndex 小于零或 *大于此实例的长度，则引发 ArgumentOutOfRangeException 。 *

Throws ArgumentOutOfRangeException if startIndex is less than zero or *greater than the length of this instance. *

换句话说，从子字符串开始直到最后一个字符都将为您提供一个空字符串。

In other words, taking a substring starting just beyond the final character will give you an empty string.

您希望它给您字符串的部分的注释与此不兼容。 字符串的一部分还包括所有长度为零的所有子字符串的集合，这由 s.substring（n，0）将也给出一个空字符串。

Your comment that you expected it to give you a part of the string is not incompatible with this. A "part of the string" includes the set of all substrings of zero length as well, as evidenced by the fact that s.substring(n, 0) will also give an empty string.

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