Mid Function

Mid Function

Class

Microsoft.VisualBasic.Strings

Syntax

 Mid(   str   ,   start   [,   length   ])

str (required; String): The expression from which to return a substring
start (required; Long): The starting position of the substring
length (optional; Long): The length of the substring

Return Value

String

Description

Returns a substring of a specified length from a given string

Rules at a Glance

If str contains Nothing , Mid returns Nothing .
If start is greater than the length of str , a zero-length string is returned.
If start is less than zero, runtime error 5, "Invalid procedure call or argument," is generated.
If length is omitted or length is greater than the length of str , all characters from start to the end of str are returned.

Example

The following example parses the contents of a text box control (named txtString ) and writes each word to a list box (named lstWord ). Note the use of the InStr function to determine the position of either a space or a carriage return/line feed character combination the two characters that can terminate a word in this case:

 Private Sub btnParse_Click(ByVal sender As System.Object, _                            ByVal e As System.EventArgs) _             Handles btnParse.Click    Dim strString, strWord As String    Dim intStart, intEnd, intStrLen, intCrLf As Integer    Dim blnLines As Boolean    lstWords.Items.Clear(  )    intStart = 1    strString = Trim(txtString.Text)    intStrLen = Len(strString)    intCrLf = InStr(1, strString, vbCrLf)    If intCrLf Then blnLines = True    lstWords.BeginUpdate(  )    Do While intStart > 0       intEnd = InStr(intStart, strString, " ") - 1       If intEnd <= 0 Then intEnd = intStrLen       If blnLines And (intCrLf < intEnd) Then          intEnd = intCrLf - 1          intCrLf = InStr(intEnd + 2, strString, vbCrLf)          If intCrLf = 0 Then blnLines = False          lstWords.Items.Add(Mid(strString, intStart, _                                 intEnd - intStart + 1))          intStart = intEnd + 3       Else          lstWords.Items.Add(Mid(strString, intStart, _                                 intEnd - intStart + 1))          intStart = intEnd + 2       End If       If intStart > intStrLen Then intStart = 0    Loop    lstWords.EndUpdate(  ) End Sub

Programming Tips and Gotchas

Use the Len function to determine the total length of str .
Use InStr to determine the starting point of a given substring within another string.