替换字符串的第二个字符

Question

我有一个字符串变量。

Dim str As String = "ABBCD"

我想替换仅限第二个＆＃39; B＆＃39; str的字符（我的意思是第二次出现）

我的代码

Dim regex As New Regex("B")
Dim result As String = regex.Replace(str, "x", 2)

'result: AxxCD
'but I want: ABxCD

使用正则表达式执行此操作的最简单方法是什么。

感谢

Answer 1

怎么样：

resultString = Regex.Replace(subjectString, @"(B)\1", "$+x");

Answer 2

使用积极的外观：

Dim regex As New Regex("(?<=B)B")

Live demo

Answer 3

如果ABCABCABC应生成ABCAxCABC，那么以下正则表达式将起作用：

(?<=^[^B]*B[^B]*)B

用法：

Dim result As String = Regex.Replace(str, "(?<=^[^B]*B[^B]*)B", "x")

Answer 4

    Dim str As String = "ABBCD"
    Dim matches As MatchCollection = Regex.Matches(str, "B")
    If matches.Count >= 2 Then
        str = str.Remove(matches(1).Index, matches(1).Length)
        str = str.Insert(matches(1).Index, "x")
    End If

Answer 5

我认为BB只是一个示例，可以是CC，DD，EE等。
基于此，下面的正则表达式将替换字符串中的任何重复字符。

resultString = Regex.Replace(subjectString, @"(\w)\1", "$1x");

Answer 6

'Alternative way to replace the second occurrence
    'only of B in the string with X
    Dim str As String = "ABBCD"
    Dim pattern As String = "B"
    Dim reg As Regex = New Regex(pattern)
    Dim replacement As String = "X"
    'find position of second B
    Dim secondBpos As Integer = Regex.Matches(str, pattern)(1).Index
    'replace that B with X
    Dim result As String = reg.Replace(str, replacement, 1, secondBpos)
    MessageBox.Show(result)