测试字符串是否以字符串开头？

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最佳答案

There are several ways to do this:

InStr

You can use the InStr build-in function to test if a String contains a substring. InStr will either return the index of the first match, or 0. So you can test if a String begins with a substring by doing the following:

If InStr(1, "Hello World", "Hello W") = 1 Then
MsgBox "Yep, this string begins with Hello W!"
End If

If InStr returns 1, then the String ("Hello World"), begins with the substring ("Hello W").

Like

You can also use the like comparison operator along with some basic pattern matching:

If "Hello World" Like "Hello W*" Then
MsgBox "Yep, this string begins with Hello W!"
End If

In this, we use an asterisk (*) to test if the String begins with our substring.

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Judging by the declaration and description of the startsWith Java function, the "most straight forward way" to implement it in VBA would either be with Left:

Public Function startsWith(str As String, prefix As String) As Boolean
startsWith = Left(str, Len(prefix)) = prefix
End Function

Or, if you want to have the offset parameter available, with Mid:

Public Function startsWith(str As String, prefix As String, Optional toffset As Integer = 0) As Boolean
startsWith = Mid(str, toffset + 1, Len(prefix)) = prefix
End Function

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The best methods are already given but why not look at a couple of other methods for fun? Warning: these are more expensive methods but do serve in other circumstances.

The expensive regex method and the css attribute selector with starts with ^ operator

Option Explicit


Public Sub test()


Debug.Print StartWithSubString("ab", "abc,d")


End Sub

Regex:

Public Function StartWithSubString(ByVal substring As String, ByVal testString As String) As Boolean
'required reference Microsoft VBScript Regular Expressions
Dim re As VBScript_RegExp_55.RegExp
Set re = New VBScript_RegExp_55.RegExp


re.Pattern = "^" & substring


StartWithSubString = re.test(testString)


End Function

Css attribute selector with starts with operator

Public Function StartWithSubString(ByVal substring As String, ByVal testString As String) As Boolean
'required reference Microsoft HTML Object Library
Dim html As MSHTML.HTMLDocument
Set html = New MSHTML.HTMLDocument


html.body.innerHTML = "<div test=""" & testString & """></div>"


StartWithSubString = html.querySelectorAll("[test^=" & substring & "]").Length > 0


End Function