Strings.InStr和Strings.InStrRev产生不同结果

Question

使用Visual Studio 2019和Visual Basic。下面的测试程序产生一个我无法解释的结果。使用InStr的前向搜索正确地找到了不区分大小写的人 CompareMethod.Text中的"joe“。但是反向搜索InStrRev没有找到"joe"...why？

Dim msg As String = "According to Joe, this is a beautiful day. Joe rides a bicycle!"
Dim joe As String = "Joe"
Dim joeLower As String = "joe"

Console.WriteLine(InStr(msg, joe))                             ' 14 => found, expected
Console.WriteLine(InStr(msg, joeLower))                        ' 0 => not found, expected
Console.WriteLine(InStr(msg, joeLower, CompareMethod.Text))    ' 14 => found, expected

Console.WriteLine(InStrRev(msg, joe))                          ' 44 => found, expected
Console.WriteLine(InStrRev(msg, joeLower))                     ' 0 => not found, expected
Console.WriteLine(InStrRev(msg, joeLower, CompareMethod.Text)) ' 0 => not found, why?

Answer 1

因为您作为第三个参数传递的是CompareMethod.Text值，而不是应该开始搜索的索引的值。默认值应为-1 (或从字符串的末尾)。

Console.WriteLine(InStrRev(msg, joeLower, -1, CompareMethod.Text)) ' => 44 

InStrRev中的最后两个参数都是可选的，因为CompareMethod.Text等于整数1，所以搜索从索引1开始，只检查一个字符，当然没有找到匹配。