DOCUMENT:Q195763 16-NOV-1998 [vbwin] TITLE :HOWTO: Use GetTempFileName API to Create a Unique Temporary File PRODUCT :Microsoft Visual Basic for Windows PROD/VER:WINDOWS:5.0,6.0 OPER/SYS:WINDOWS KEYWORDS:kbVBp kbVBp500 kbVBp600 kbAPI kbSDKWin32 kbCodeSam kbKernBase ====================================================================== --------------------------------------------------------------------- The information in this article applies to: - Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, versions 5.0, 6.0 --------------------------------------------------------------------- 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. MORE INFORMATION ================ 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 -------------------- 1. Create a new Standard EXE project. Form1 is created by default. 2. Add a CommandButton to Form1. 3. 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 4. 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. REFERENCES ========== For additional information, please see the following articles in the Microsoft Knowledge Base: ARTICLE-ID: Q190000 TITLE : HOWTO: Get Started Programming With the Windows API (LONG) ARTICLE-ID: Q137034 TITLE : PRB: Win32 GetTempFileName API Differs from 16-bit (c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Richard R. Taylor, Microsoft Corporation. Additional query words: ====================================================================== Keywords : kbVBp kbVBp500 kbVBp600 kbAPI kbSDKWin32 kbCodeSam kbKernBase Version : WINDOWS:5.0,6.0 Platform : WINDOWS Issue type : kbhowto ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 1998.