Microsoft KB Archive/195763

= How To Use GetTempFileName API to Create a Unique Temporary File =

Article ID: 195763

Article Last Modified on 8/30/2004

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APPLIES TO


 * Microsoft Visual Basic 5.0 Learning Edition
 * Microsoft Visual Basic 6.0 Learning Edition
 * Microsoft Visual Basic 5.0 Professional Edition
 * Microsoft Visual Basic 6.0 Professional Edition
 * Microsoft Visual Basic 5.0 Enterprise Edition
 * Microsoft Visual Basic 6.0 Enterprise Edition

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This article was previously published under Q195763



SUMMARY
For Visual Basic programmers unfamiliar with the Win32 API, making a file name for a temporary file is often a matter of hard-coding some value and hoping that the name does not conflict with an existing file. Fortunately, there is a better way that requires very little code.

This article demonstrates how to use the GetTempPath and GetTempFileName API functions to construct a unique temporary file name located in the default temp directory of an end user's system.



GetTempPath
The GetTempPath API function allows you to determine the path location of a system's temporary folder. It takes two parameters: the length of a fixed- length or pre-initialized string that will contain the path name, and the string itself. You must use either a fixed-length string, or a string initialized to a length that you believe will be long enough to contain the path information. This is to guarantee that Visual Basic allocates enough buffer space for Windows to return the information.

GetTempPath returns the length of the path name measured in bytes, or 0 if an error occurs. If the return value is greater than the buffer size you specified, then no path information was written to the string.

The declaration for GetTempPath is provided in the sample below.

GetTempFileName
The GetTempFileName API function is used to create a fully-qualified temporary file name at a given location. The function takes four parameters: the string containing the path for the file, a string containing a prefix used to start the unique file name, a unique number to construct the temp name, and, finally, a fixed-length or pre-initialized string used to return the fully qualified file name. Both the path and prefix strings are required and cannot be empty. The unique number can be 0 (NULL), in which case GetTempFileName creates a unique number based on the current system time.

GetTempFileName returns the unique number used to create the file name, or returns 0 if an error occurs.

The declaration for GetTempFileName is provided in the sample below.

Step-by-Step Example
 Create a new Standard EXE project. Form1 is created by default. Add a CommandButton to Form1.  Add the following code to the General Declarations section of Form1: Option Explicit

Private Declare Function GetTempPath Lib "kernel32" _ Alias "GetTempPathA" (ByVal nBufferLength As Long, _        ByVal lpBuffer As String) As Long

Private Declare Function GetTempFileName Lib "kernel32" _ Alias "GetTempFileNameA" (ByVal lpszPath As String, _        ByVal lpPrefixString As String, ByVal wUnique As Long, _         ByVal lpTempFileName As String) As Long

Private Function CreateTempFile(sPrefix As String) As String Dim sTmpPath As String * 512 Dim sTmpName As String * 576 Dim nRet As Long

nRet = GetTempPath(512, sTmpPath) If (nRet > 0 And nRet < 512) Then nRet = GetTempFileName(sTmpPath, sPrefix, 0, sTmpName) If nRet <> 0 Then CreateTempFile = Left$(sTmpName, _                 InStr(sTmpName, vbNullChar) - 1) End If        End If      End Function

Private Sub Command1_Click Dim sTmpFile As String Dim sMsg As String Dim hFile As Long

sTmpFile = CreateTempFile("VBT") hFile = FreeFile

Open sTmpFile For Binary As hFile Put #hFile,, "This is a test. 1234" Close hFile

sMsg = "Temp FileName: " & sTmpFile & vbCrLf sMsg = sMsg & "File Length: " & FileLen(sTmpFile) & vbCrLf sMsg = sMsg & "Time Created: " & _ Format$(FileDateTime(sTmpFile), "long time") & vbCrLf

MsgBox sMsg, vbInformation, "TempFile"

Kill sTmpFile End Sub

 Press the F5 key to run the project. When you click the CommandButton, a temporary file is created. A message box displays information regarding the temp file. The file is then destroyed using the Kill statement.

