如何计算字符的长度和截取字符（小节）

如何计算字符的长度和截取字符（小节）

在此之前，有很多问题问如何判断输入的字符的长度，一般情况很多的人都说一个一个的字取判断，还有全角判断，两种方法：
一：
Public Function GetStringLengthB(ByVal checkString As String) As Integer

Dim firstB As String
Dim asc As Integer
Dim i As Integer
Dim count As Integer
Dim stringLength As Integer
Dim strKana As String

strKana = "ｱｲｳｴｵｶｷｸｹｺｻｼｽｾｿﾀﾁﾂﾃﾄﾅﾆﾇﾈﾉﾊﾋﾌﾍﾎﾏﾐﾑﾒﾓﾔﾕﾖﾗﾘﾙﾚﾛﾜｦﾝｧｨｩｪｫｬｭｮ､｡｢｣ﾞﾟ"

If Microsoft.VisualBasic.Trim(checkString) = "" Then
Return 0
End If

stringLength = checkString.Length
count = 0

For i = 1 To stringLength
firstB = Microsoft.VisualBasic.Mid(checkString, i, 1)
asc = Microsoft.VisualBasic.AscW(firstB)

If asc < 0 Or asc > 255 Then

If strKana.IndexOf(firstB) = -1 Then
count = count + 2
Else
count = count + 1
End If
Else
count = count + 1
End If
Next

Return count
End Function

二：
Private Function GetLength(ByVal str As String) As Integer
Dim encodingData() As Byte

encodingData = System.Text.Encoding.Default.GetBytes(str)
Return encodingData.Length
End Function

对于字符的截取那就可以采用第二种方法，是以位截取，不是以个数截取。
Private Function GetLength(ByVal str As String,Byval length as string) As string
Dim encodingData() As Byte

encodingData = System.Text.Encoding.Default.GetBytes(str)
If length < encodingData.Length Then
Return System.Text.Encoding.Default.GetString(encodingData, 0, length )
Else
Return str
End If

End Function