Q69216: How to Change Attributes of Subdirectories in a C Program

Article: Q69216
Product(s): See article
Version(s): 3.x 4.x 5.x 6.00 6.00a | 5.10 6.00 6.00a
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | | mspl13_c
Last Modified: 25-FEB-1991

The C run-time functions _dos_setfileattr() and _dos_getfileattr(), or
the OS/2 API calls DosSetFileMode() and DosQFileMode(), respectively,
allow you to set and check the attributes of files. When using the
same functions on subdirectories, the operating system does not allow
attributes to be set, and no error codes are returned. However,
because a subdirectory is a special instance of a file, the system can
be fooled into thinking that a subdirectory is a file, which will
allow you to set the attributes of a subdirectory.

Below is a listing of available attribute settings:

   C Run-Time   OS/2            Description                  Value
   ----------   ----            -----------                  -----

   _A_NORMAL    FILE_NORMAL     A file with no attributes    0x00
   _A_RDONLY    FILE_READONLY   A read-only file             0x01
   _A_HIDDEN    FILE_HIDDEN     A hidden file                0x02
   _A_SYSTEM    FILE_SYSTEM     A system file                0x04
   _A_VOLID     *               Volume label (special case)  0x08
   _A_SUBDIR    FILE_DIRECTORY  Subdirectory (special case)  0x10
   _A_ARCH      FILE_ARCHIVED   An archived file             0x20

 * A drive's volume label is another special-case file; there is only
   one per (logical) drive, and it is only in the root directory.
   Under OS/2, volume labels can be changed with DosSetFSInfo. Under
   DOS, there are no C run-time functions to change drive volumes. For
   more information, query on the following words:

      volume and attribute and 5.10

From the list above, the only attributes that can be dynamically set
are FILE_READONLY, FILE_HIDDEN, and FILE_SYSTEM (all files,
subdirectories, and volumes entail FILE_NORMAL), and this process
cannot be done on a directory entry that is flagged as a subdirectory
or volume label. To change the attributes of a subdirectory, the
attribute flag _A_SUBDIR (or FILE_DIRECTORY) should not be included.
The code below demonstrates how to do this using either C run-time
calls (DOS only) or OS/2 API functions (DOS and OS/2 if bound).

Sample Code
-----------

#define INCL_DOSFILEMGR
#include <os2.h>

#include <dos.h>
#include <stdlib.h>

unsigned attr, newattr;

void main(void)
{
   if (DOS_MODE == _osmode)
      {
      // First get the current attribute of subdirectory '\foo'
      // If successful, 'attr' will contain at least the
      // _A_SUBDIR bit mask

      _dos_getfileattr( "\\foo", &attr );

      // Mask in new attributes and remove _A_SUBDIR from the old
      // attribute

      newattr = (attr | _A_HIDDEN | _A_SYSTEM | _A_RDONLY)
                  & ~_A_SUBDIR;

      // Set new attribute for 'foo'

      _dos_setfileattr( "\\foo", newattr );
      }
   else     // Here is the same using OS/2 APIs
      {
      DosQFileMode( "\\foo", &attr, 0L );

      newattr = (attr | FILE_HIDDEN | FILE_SYSTEM | FILE_READONLY)
                  & ~FILE_DIRECTORY;

      DosSetFileMode( "\\foo", newattr, 0L );
      }
}

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