GetTempFileName

The GetTempFileName function creates a name for a temporary file. The filename is the concatenation of specified path and prefix strings, a hexadecimal string formed from a specified integer, and the .TMP extension.

The specified integer can be nonzero, in which case, the function creates the filename but does not create the file. If you specify zero for the integer, the function creates a unique filename and creates the file in the specified directory.

UINT GetTempFileName(
  LPCTSTR lpPathName,  // pointer to directory name for temporary 
                       // file
  LPCTSTR lpPrefixString,  // pointer to filename prefix
  UINT uUnique,        // number used to create temporary filename
  LPTSTR lpTempFileName 
                       // pointer to buffer that receives the new 
                       // filename
);
 

Parameters

lpPathName

Pointer to a null-terminated string that specifies the directory path for the filename. This string must consist of characters in the ANSI character set. Applications typically specify a period (.) or the result of the GetTempPath function for this parameter. If this parameter is NULL, the function fails.

lpPrefixString

Pointer to a null-terminated prefix string. The function uses the first three characters of this string as the prefix of the filename. This string must consist of characters in the ANSI character set.

uUnique

Specifies an unsigned integer that the function converts to a hexadecimal string for use in creating the temporary filename.

If uUnique is nonzero, the function appends the hexadecimal string to lpPrefixString to form the temporary filename. In this case, the function does not create the specified file, and does not test whether the filename is unique.

If uUnique is zero, the function uses a hexadecimal string derived from the current system time. In this case, the function uses different values until it finds a unique filename, and then it creates the file in the lpPathName directory.

lpTempFileName

Pointer to the buffer that receives the temporary filename. This null-terminated string consists of characters in the ANSI character set. This buffer should be at least the length, in bytes, specified by MAX_PATH to accommodate the path.

Return Values

If the function succeeds, the return value specifies the unique numeric value used in the temporary filename. If the uUnique parameter is nonzero, the return value specifies that same number.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The GetTempFileName function creates a temporary filename of the following form:

path\preuuuu.TMP

The following table describes the filename syntax:

When the system shuts down, temporary files whose names have been created by this function are not automatically deleted.

To avoid problems resulting when converting an ANSI string, an application should call the CreateFile function to create a temporary file.

If the uUnique parameter is zero, GetTempFileName attempts to form a unique number based on the current system time. If a file with the resulting filename exists, the number is increased by one and the test for existence is repeated. Testing continues until a unique filename is found. GetTempFileName then creates a file by that name and closes it. When uUnique is nonzero, no attempt is made to create and open the file.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Unsupported.
  Header: Declared in winbase.h.
  Import Library: Use kernel32.lib.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT.

See Also

File I/O Overview, File Functions, CreateFile, GetTempPath