正则表达式 - 量词 {x,y} 不跟任何东西 [英] Regex - Quantifier {x,y} following nothing

问题描述

我正在创建一个基本的文本编辑器，我正在使用正则表达式来实现查找和替换功能.为此，我得到了以下代码:

I'm creating a basic text editor and I'm using regex to achieve a find and replace function. To do this I've gotten this code:

Private Function GetRegExpression() As Regex
    Dim result As Regex
    Dim regExString As [String]
    ' Get what the user entered
    If TabControl1.SelectedIndex = 0 Then
        regExString = txtbx_Find2.Text
    ElseIf TabControl1.SelectedIndex = 1 Then
        regExString = txtbx_Find.Text
    End If

    If chkMatchCase.Checked Then
        result = New Regex(regExString)
    Else
        result = New Regex(regExString, RegexOptions.IgnoreCase)
    End If

    Return result
End Function

这就是Find方法

 Private Sub FindText()
    ''
    Dim WpfTest1 As New Spellpad.Tb
    Dim ElementHost1 As System.Windows.Forms.Integration.ElementHost = frm_Menu.Controls("ElementHost1")
    Dim TheTextBox As System.Windows.Controls.TextBox = CType(ElementHost1.Child, Tb).ctrl_TextBox
    ''
    ' Is this the first time find is called?
    ' Then make instances of RegEx and Match
    If isFirstFind Then
        regex = GetRegExpression()
        match = regex.Match(TheTextBox.Text)
        isFirstFind = False
    Else
        ' match.NextMatch() is also ok, except in Replace
        ' In replace as text is changing, it is necessary to
        ' find again
        'match = match.NextMatch();
        match = regex.Match(TheTextBox.Text, match.Index + 1)

    End If

    ' found a match?
    If match.Success Then
        ' then select it
        Dim row As Integer = TheTextBox.GetLineIndexFromCharacterIndex(TheTextBox.CaretIndex)
        MoveCaretToLine(TheTextBox, row + 1)
        TheTextBox.SelectionStart = match.Index
        TheTextBox.SelectionLength = match.Length

    Else
        If TabControl1.SelectedIndex = 0 Then
            MessageBox.Show([String].Format("Cannot find ""{0}""   ", txtbx_Find2.Text), Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Information)
        ElseIf TabControl1.SelectedIndex = 1 Then
            MessageBox.Show([String].Format("Cannot find ""{0}""   ", txtbx_Find.Text), Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Information)
        End If
        isFirstFind = True
    End If
End Sub

当我运行程序时出现错误:

When I run the program I get errors:

• 对于?，解析?"- 量词 {x,y} 后面没有.;和
• 对于*，解析*" - 量词{x,y}后面什么都没有.

好像我不能使用这些，但我真的需要.我该如何解决这个问题?

It's as if I can't use these but I really need to. How can I solve this problem?

推荐答案

? 和 * 是正则表达式中的量词:

? and * are quantifiers in regular expressions:

• ? 用于指定某些东西是可选的，例如 b?au 可以匹配 bau 和 au.
• * 表示它所绑定的组可以重复零次、一次或多次:例如 ba*u 可以洗澡 bu, bau, baau, baaaaaaaau,...

• ? is used to specify that something is optional, for instance b?au can match both bau and au.
• * means the group with which it binds can be repeated zero, one or multiple times: for instance ba*u can bath bu, bau, baau, baaaaaaaau,...

现在大多数正则表达式使用{l,u}作为第三种模式，l是某事物次数的下限重复，u 是出现次数的上限.所以 ? 被 {0,1} 替换，* 被 {0,} 替换.

Now most regular expressions use {l,u} as a third pattern with l the lower bound on the number of times something is repeated, and u the upper bound on the number of occurences. So ? is replaced by {0,1} and * by {0,}.

现在，如果您在它们之前提供没有任何字符，显然正则表达式解析器不知道您的意思.换句话说，如果你这样做(使用了csharp，但这些想法普遍适用):

Now if you provide them without any character before them, evidently, the regex parser doesn't know what you mean. In other words if you do (used csharp, but the ideas are generally applicable):

$ csharp
Mono C# Shell, type "help;" for help

Enter statements below.
csharp> Regex r = new Regex("fo*bar");
csharp> r.Replace("Fooobar fooobar fbar fobar","<MATCH>");    
"Fooobar <MATCH> <MATCH> <MATCH>"
csharp> r.Replace("fooobar far qux fooobar quux fbar echo fobar","<MATCH>");
"<MATCH> far qux <MATCH> quux <MATCH> echo <MATCH>"

如果您希望执行原始文本查找和替换"，您应该使用 string.Replace.

If you wish to do a "raw text find and replace", you should use string.Replace.

编辑:

另一种处理它们的方法是转义特殊的正则表达式字符.具有讽刺意味的是，您可以通过用正则表达式替换它们来做到这一点；)

Another way to process them is by escaping special regex characters. Ironically enough, you can do this by replacing them by a regex ;).

Private Function GetRegExpression() As Regex
    Dim result As Regex
    Dim regExString As [String]
    ' Get what the user entered
    If TabControl1.SelectedIndex = 0 Then
        regExString = txtbx_Find2.Text
    ElseIf TabControl1.SelectedIndex = 1 Then
        regExString = txtbx_Find.Text
    End If

    'Added code
    Dim baseRegex As Regex = new Regex("[\\.$^{\[(|)*+?]")
    regExString = baseRegex.Replace(regExString,"\$0")
    'End added code

    If chkMatchCase.Checked Then
        result = New Regex(regExString)
    Else
        result = New Regex(regExString, RegexOptions.IgnoreCase)
    End If

    Return result
End Function

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