Tip 1: Determining If a File Already Exists

Created: March 1, 1995

Abstract

The Windows® function OpenFile provides a reliable method of determining whether or not a specific filename or path name exists.

The information in this article applies to:

Standard and Professional Editions of Microsoft® Visual Basic® for Windows, versions 2.0 and 3.0.
Microsoft Visual Basic programming system for Windows, version 1.0.

OpenFile Function

The OpenFile function can be used to perform several file operations, such as creating a new file, deleting a file, or determining if a file exists. To declare this function within your program, include the following Declare statement in the Global Module or General Declarations section of a Visual Basic® for Windows® form:

Declare Function OpenFile% Lib "Kernel" (ByVal lpFileName$, lpReOpenBuff
    As OFSTRUCT, ByVal wStyle%)

Note that this Declare statement must be typed as one single line of text.

The OpenFile function takes the following arguments, described as follows:

Argument	Description
lpFileName	A string containing the name, which may or may not include a path name, to test.
lpReOpenBuff	An OFSTRUCT structure that will contain information about the file after the OpenFile function has been called.
wStyle	This combination of one or more flags specifies the type of operation that is to be performed on the file.

In our demonstration program, we need only specify wStyle as the constant OF_EXIST.

After calling the OpenFile function, an integer value is returned. If a negative number is returned, the nErrCode value in the OFSTRUCT structure can be examined to find out if the file exists already.

Example Program

The following program demonstrates how to determine if a file already exists.

Start a new project in Visual Basic. Form1 is created by default.

Add the following code to the Global Module:

'OFSTRUCT structure used by the OpenFile API function
Type OFSTRUCT            '136 bytes in length
    cBytes As String * 1
    fFixedDisk As String * 1
    nErrCode As Integer
    reserved As String * 4
    szPathName As String * 128
End Type

Within the Global Declaration section of Form1, add the following Windows function declaration (note that this Declare statement must be typed as one single line of text):
```
Declare Function OpenFile% Lib "Kernel" (ByVal lpFileName$, lpReOpenBuff As OFSTRUCT, ByVal wStyle%)
```

Next, add the following lines of code to the Global Declaration section of Form1:

Dim wStyle As Integer
Dim Buffer As OFSTRUCT
Dim IsThere As Integer
Dim TestFile As String

Add the following code to the Form_Load() event procedure:

Sub Form_Load()
    TestFile = "c:\testfile.dat"
    IsThere = OpenFile(TestFile, Buffer, OF_EXIST)
    If  IsThere < 0 Then
        GoTo CheckForError
        Else
        Debug.Print "This file already exists"
    End If
    CheckForError:
    IsThere = Buffer.nErrCode
    If  IsThere = 3 Then
        Debug.Print "Pathname not found"
    End If