Tip 65: Separating a Path into Individual Fields

* VB-CODE (3)

Abstract
When developing an application in Visual Basic®, you may need to ask
the user to enter a fully qualified path, such as when saving a data
file to disk. However, your program may need to determine if the
specified directory and filename are valid DOS names, or you may need
to use the individual elements of the path in some other way. This
article demonstrates how you can write a procedure to extract the
individual path, filename, and filename extension from a fully
qualified path.

Parsing the Elements of a Path
The Visual Basic® InStr and Left$ functions provide the tools you
need to parse, or extract, certain text from a larger text string.
The InStr function lets you search for a specific character within
a text string. If it finds the target character, InStr returns the
character's position in the text string. Once you know where the
target text is, you can use the Left$ function to retrieve only a
specific portion of the original text string. In the example program
below, we want to retrieve the directory name from the path.
Therefore, we first call InStr to search the target string (Full) for
the "\" backslash character. The backslash character tells us that
the name of a directory was specified in the path. If the backslash
character is found, we use the Left$ function to extract this
directory name and store it in the variable Pname. We know that the
name of the directory starts at the string's first position and ends
at the position returned by InStr. This same technique is used to
extract the filename extension from the specified filename, only the

nStr function is told to search for the '.' (period character) and
the Mid$ function is used to extract the actual filename's extension.

Example Program
The following program shows how you can separate a fully qualified
path into separate directory, filename, and filename extension fields.

1. Create a new project in Visual Basic. Form1 is created by default.
2. Add a Text Box control to Form1. Text1 is created by default. Set
   its MultiLine property to True.
3. Add the following code to the Form_Load event for Form1:

Sub Form_Load()
 Dim FullName As String
 Dim X As Integer
 Dim PathName As String
 Dim FileName As String
 Dim ExtName As String

 FullName = "c:\winword\legal\filename.exe"
 X = BreakDown(FullName, FileName, PathName, ExtName)

 Text1.Text = ""
 Text1.Text = "Pathname  > " & PathName & Chr(13) & Chr(10)
 Text1.Text = Text1.Text & "FileName  > " & FileName & Chr(13) & Chr(10)
 Text1.Text = Text1.Text & "Extension > " & ExtName & Chr(13) & Chr(10)
End Sub

4. Create a new function called BreakDown. Add the following code to
   this function (note that the BreakDown line must be typed as a
   single line of code):

BreakDown(Full As String, FName As String, PName As String, Ext As String) As Integer
 If Full = "" Then
     BreakDown = False
     Exit Function
 End If
 If InStr(Full, "\") Then
     FName = Full
     PName = ""
     Sloc% = InStr(FName, "\")
     Do While Sloc% <> 0
       PName = PName + Left$(FName, Sloc%)
       FName = Mid$(FName, Sloc% + 1)
       Sloc% = InStr(FName, "\")
     Loop
 Else
     PName = ""
     FName = Full
 End If
 Dot% = InStr(Full, ".")
 If Dot% <> 0 Then
     Ext = Mid$(Full, Dot%)
 Else
     Ext = ""
 End If
 BreakDown = True
End Function