c# - 为什么 C# 的 LastIndexOf 会这样？

Question

我有以下代码:

string s = "Hello, World!";
Console.WriteLine(s.LastIndexOf("World"));//7
Console.WriteLine(s.LastIndexOf("World", 7));//-1

为什么第二次调用 LastIndexOf 的结果是 -1 而不是 7？

Answer 1

来自 MSDN :

The search begins at the startIndex character position of this instance and proceeds backward toward the beginning until either value is found or the first character position has been examined. For example, if startIndex is Length - 1, the method searches every character from the last character in the string to the beginning.

由于向后搜索，所以在 7 之前没有包含 World 的索引。