from http://mc-computing.com/Languages/VisualBasic/VBFileIO.htm
File I/O - VisualBasic Examples
- File Manager Commands
- File I/O Commands
- File Access via a FileSystemObject
- Standard Open File Dialog
- Specifying a Drive and Path
- Opening and Reading a File
- File SaveAs
- Testing for a Legal Filename
- Testing for the Existance of a File
- Testing for the Existance of a Drive
File Manager Commands
| Change Directory | ChDir "c:\path" |
| Make Directory | MkDir "c:\path" |
| Remove Directory | RmDir "c:\path" |
| Change Drive | ChDrive "d" |
| Rename a File | Name "test.txt" as "string.tst" (May fail if directories are not specified) |
| Delete a File | Kill "c:\*.tst" |
| Search for File | temp$ = Dir ("c:\*.tst") |
| Current Drirectory | temp$ = CurDir ("d") ' Drive letter is optional |
| Get File Attributes | temp = GetAttr ("c:\filename.tst") |
| Get File Mode | temp = FileAttr ("c:\filename.tst", attributes) |
| Set File Attributes | SetAttr "c:\filename.tst", vbReadOnly |
| Get File Length | FileLen ("c:\filename.tst") |
| Get File Date/Time | tempDate = FileDateTime ("c:\filename.tst") |
| Set File Date/Time | ???? |
File I/O Commands
| Open File for I/O | Open "c:\filename.tst" For Input As 3 fn = FreeFile ' next unused number Open "c:\filename.tst" For Input As fn |
| Get File Mode | temp = FileAttr (3, 1) |
| Write to File | Write 3, |
| Write to File | Print 3, |
| Read From File | Input 3, |
| Read From File | Get 3, |
| Read From File | Line Input #FileHandle, TextLine$ |
| Current Location | tempNum = Seek (3) |
| Current Location | tempNum = Loc (3) |
| Length of File | tempNum = LOF(3) |
| End of File | Do While Not EOF(3) .. Loop |
| Close File | Close 3 |
| Closes All Files | Reset |
Write places strings in double quotes, separates values with commas, and adds a CR/LF pair at the end of each command. Read the data back with Input.
Print does not add extra delimiters, but does concatenate a final CR/LF to each line. The CR/LF can be suppressed by ending the command with a semicolon (;). (This trick has been available in every Basic I've used, but it is not documented in the VB 6.0 Help.) Read it back with Line Input. (Line Input assumes a DOS type ASCII input file where each line is terminated with CR/LF. It does not recognize the unix line termination character.)
File Access via a FileSystemObject
Set fs = CreateObject("Scripting.FileSystemObject") Set a = fs.CreateTextFile("c:\testfile.txt", True) a.WriteLine("This is a test.") a.Close See the help for additional details.
Standard Open File Dialog
- The Common Dialog installation instructions tell you to install the wrong file. (Commdlg.dll - a 16-bit dll !!!)
- The Filename property is missing from the help.
Selecting a File to Open
- Right click on the ToolBox and select Components...
- Scroll down and check Microsoft Common Dialog Controls
- Place the component on your form and name it CMDialog
- Attach the following code to a menu selection
Dim TestFile$ ' String variable CMDialog.Filter = "Test (*.tst)|*.tst" CMDialog.InitDir = "C:\SomePath" CMDialog.Action = 1 ' VB 4.0 way to select FileOpen ' Still works in VB 6.0 CMDialog.ShowOpen ' VB 6.0 way to select FileOpen TestFile$ = CMDialog.FileName ' = "" if the Cancel button is pressed If TestFile$ <> "" Then Main_UIForm.Caption = _ "Application Name or Function - " + CMDialog.FileTitle Call SomeProcedure(TestFile$) End If
| CMDialog.FileName | File name and path |
| CMDialog.FileTitle | File name without the path |
Notice that by default, CMDialog changes the default path! Setting a bit in the flag property will prevent this.
The help for the common Dialog FileName property says to use the Path property to get the related path. However, if you use CMDialog.Path you get an
- Method or data member not found
Specifying a Drive and Path
Select_Directory_UIForm.Tag = UIDirListBox.List(UIDirListBox.ListIndex)to return the selected directory. Null means that Cancel was selected.
Use the DriveListBox control to change drives. The following code is adequate.
Private Sub UIDriveListBox_Change() UIDirListBox.Path = UIDriveListBox.Drive End Sub
Opening and Reading a File
Dim TextLine$, Filename$ Dim FileHandle as Integer Filename$ = "test.txt" ' Test if the file exists If Dir(Filename$) = "" Then Exit Sub FileHandle = FreeFile ' This is safer than assigning a number Open Filename$ For Input As #FileHandle Do While Not EOF(FileHandle) ' Loop until end of file Line Input #FileHandle, TextLine$ ' Read line into variable ' Your code here Loop Close #FileHandleLine Input assumes a DOS type ASCII input file where each line is terminated with CR/LF. It does not recognize the unix line termination character.
File SaveAs
Dim fs 'As FileSystemObject Dim OldPath$ OldPath$ = CurDir ' CMDialog will change the current path Set fs = CreateObject("Scripting.FileSystemObject") If Not fs.FileExists("Test.txt") Then Exit Sub CMDialog.Flags = cdlOFNHideReadOnly + cdlOFNExplorer CMDialog.Filter = "Test (*.tst)|*.tst" CMDialog.FileName = "" ' This is the value returned if Esc/Cancel CMDialog.Action = 2 ' VB 4.0 way to select FileSaveAs CMDialog.ShowSave ' VB 6.0 way to select FileSaveAs TestFile$ = CMDialog.FileName ' = "" if the Cancel button is pressed If TestFile$ <> "" Then ' If OverWrite, ask if ok If Dir(TestFile$) <> "" Then Select Case MsgBox("Overwrite existing file?", vbOKCancel) Case vbOK Kill (TestFile$) ' of course, this is wrong ' re-name the old file and erase it ' after the new file is written Case Else Exit Sub End Select End If Name OldPath$ & "\Test.txt" As TestFile$ End If Notice that CMDialog changes the default path!
Testing for a Legal Filename
' Directory and file names can not contain the following ' \ / : * ? " < > | ' Though allowed, the ampersand will also cause problems in NT ' Paths can contain : \ ' Dim crlf$, badChars$, badChars2$, i, tt$ crlf$ = Chr(13) & Chr(10) badChars$ = "\/:*?""<>|" ' For Testing, no spaces badChars2$ = "\ / : * ? "" < > |" ' For Display, has spaces ' Check for bad characters For i = 1 To Len(tt$) If InStr(badChars$, Mid(tt$, i, 1)) <> 0 Then temp = MsgBox("A directory name may not contain any of the following" _ & crlf$ & crlf$ & " " & badChars2$, _ vbOKOnly + vbCritical, _ "Bad Characters") Exit Sub End If Next i
Testing for the Existance of a File
Dim fs ' The help does not say what type this should be ' therefore, I tried a variant Set fs = CreateObject("Scripting.FileSystemObject") If Not fs.FileExists("Test.tst") Then Exit Sub Scripting is a keyword which is not documented in the help outside this one example. |
Use the Dir function to check if specific files and directories exist. The first call to Dir should contain a path and any wild cards. Subsequent calls without parameters will return the next matching filename or a null string if there is no match. Temp$ = Dir("*.tst") ' Get the first tst file Temp$ = Dir("c:\", vbDirectory) ' Get the first directory name ' in the indicated path Do While Temp$ <> "" ' Loop till there is no match ' Place main routine here Temp$ = Dir ' Get next matching filename Loop Both Dir and Dir(, vbDirectory) ignore the file attributes and return the next "file" in the last referenced directory. (Under DOS, sub-directories are simply files with the Directory attribute set.) Use GetAttr to test specific attributes. Remember that all sub-directories contain references to files named "." and ".." |
Testing for the Existance of a Drive
' Returns null if the drive does not exist ' or if the root directory is empty a$ = Dir ("C:\") A better solution is (Source: Trevor Daniel at British Telecom via comp.lang.basic.visual.misc)
Private Declare Function GetDriveType Lib "kernel32" Alias "GetDriveTypeA" (ByVal sDrive As String) As Long Private Function DriveType(DriveStr As String) As String Dim DriveTypeLong As Long Dim aa As String Const DRIVE_TYPE_UNDETERMINED = 0 Const DRIVE_ROOT_NOT_EXIST = 1 Const DRIVE_REMOVEABLE = 2 Const DRIVE_FIXED = 3 Const DRIVE_REMOTE = 4 Const DRIVE_CDROM = 5 Const DRIVE_RAMDISK = 6 aa = DriveStr & ":" DriveTypeLong = GetDriveType(aa) Select Case DriveTypeLong Case DRIVE_TYPE_UNDETERMINED DriveType = aa & " is not a recognised drive type" Case DRIVE_ROOT_NOT_EXIST DriveType = "The drive " & aa & " does not exit" Case DRIVE_CDROM DriveType = aa & " is a CD-ROM driver" Case DRIVE_FIXED DriveType = aa & " is a Hard Disk" Case DRIVE_RAMDISK DriveType = aa & " is a RAM Disk" Case DRIVE_REMOTE DriveType = aa & " is a network drive" Case DRIVE_REMOVEABLE DriveType = aa & " is a Floppy Disk" End Select End FunctionIn order to see all the Windows API file functions, search the MS Visual Studio help for GetDriveType and click on File Functions.
It is not clear why the Windows constants need to be manually defined.
Author: Robert Clemenzi - clemenzi@cpcug.org
URL: http:// cpcug.org / user / clemenzi / technical / Languages / VisualBasic / VBFileIO.htm
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