Many of the directories that appear in INF files can be expressed using directory identifiers (dirids), which are numbers that identify specific directories. Applications can use, but cannot reassign the system-defined directories that are associated with dirids whose values are from -1 through 32767. To create dirids with user-defined values from 32768 through 65534, or 65536 and up, use the SetupSetDirectoryId function (described in the Microsoft Windows SDK documentation). Note that for compatibility with Windows 9x/Me, dirid 65535 is considered to be synonymous with dirid -1, although the latter (dirid -1) is preferred.

If you intend to use dirids in your INF file, consider the following two guidelines:

1. When the syntax for an INF file entry explicitly specifies a dirid value (the INF DestinationDirs section, for example), express that value as a number. Here is an example:

   [DestinationDirs]
   DefaultDestDir = 11  ;  \system32 directory on NT-based systems
   
   

2. When the syntax for an INF file entry specifies a file path, you can use a system-supplied string substitution to represent part or all of this path. This substitution has the following form:

   %dirid%

   This form consists of a percent (%) character, followed by the dirid for the directory you want to specify, followed by another percent (%) character. A terminating backslash (\) character separates this expression from a following file name or additional directories in the path.

   The following example demonstrates this syntax.

   [aic78xx_Service_Inst]
   ServiceBinary = %12%\aic78xx.sys
   
   

   When fully expanded, the path shown in the previous example becomes c:\windows\system32\drivers\aic78xx.sys (assuming that Windows was installed in the c:\windows directory). Note that the string substitution, or %dirid% form, can be used anywhere a string is expected, with the exception of the INF Strings section of the INF file.

   The two following examples show how string substitution should not be used.

   [DestinationDirs]
   DefaultDestDir = %11%  ; Error! - number expected
   
   [aic78xx_Service_Inst]
   ServiceBinary = 12\aic78xx.sys  ; Error! - unknown directory name
   
   

   In the first example, the syntax for the DefaultDestDir entry requires its value to be a number, but the %11% expression expands to a string. In the second example, the INF writer apparently intended to set the value for the ServiceBinary entry to a file in the directory containing drivers (see the following table for more information). The error occurs because Setup looks for the specified file in a directory named "12", which probably does not exist on the machine.

The following table shows several commonly-used dirids, and the directories they represent. The values most commonly specified by device INF files and driver INF files are listed toward the top of the table.

Dirid values from 16384 through 32767 are reserved for special shell folders. The following table shows dirid values for these folders.

Besides the values listed in this table that are defined in setupapi.h, you can use any of the CSIDL_Xxx values defined in shlobj.h. To define a dirid value for a folder not listed in this table, add 16384 (0x4000) to the CSIDL_Xxx value. For more information about CSIDL_Xxx values, see the Windows SDK documentation.