PRB: rename() Function May Fail Unexpectedly

• The C Run-time (CRT) included with: - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 4.0, 5.0

SYMPTOMS

Using the rename() function to change a subdirectory name may fail if the directory name you want to change is the current working directory for that drive. In addition, some versions of MS-DOS may return a success value, but the directory name apparently has not changed.

CAUSE

An access violation occurs attempting to rename the current directory.

RESOLUTION

To work around this problem, use the chdir() function to set the current directory of the specified drive to be the root directory on the drive. However, in Windows NT, this procedure does not guarantee success because an error occurs if another process uses the target directory.

You can optimize this method by checking the active directory on the target drive. Change directories only if the directory to rename is the current directory.

MORE INFORMATION

In MS-DOS versions 3.x when SHARE.EXE is not installed, the sample program shown below produces the following results:

   C:\>cd olddir
   C:\OLDDIR>d:
   D:>test
   Rename is successful  <--- Output from test program
   D:>c:
   C:\OLDDIR>      <--- The old directory is not renamed

   C:\>cd olddir
   C:\OLDDIR>d:
   D:>test
   Rename fails with errno = 13  <--- Output from test program
   D:>c:
   C:\OLDDIR>            <--- The old directory is not renamed

This behavior does not indicate a problem with the rename() function. It simply maps to an Interrupt 21h, Function 56h (Rename File) call in MS-DOS. The problem occurs because the operating system maintains a list of the current working directory (CWD) for each drive in its drive table in memory.

In the MS-DOS 3.x example, the program successfully changed the directory name. However, because MS-DOS does not recognize the change, it does not update the CWD in the drive table. When the program ends, MS-DOS displays an invalid prompt that reflects the old directory name. If you type "CD \NEWDIR" at the MS-DOS prompt, the drive table is updated.

In the second example, MS-DOS 3.3 with SHARE.EXE installed, MS-DOS versions 4.x and later, and MS-DOS running in OS/2 cannot determine if another process is using the directory and an access violation error occurs.

In Windows NT, if any process is active in the target directory, the system does not change the directory name. When this happens, the function returns an error code 13 that indicates an access violation.

Sample Code

#include <io.h>
#include <stdio.h>

char szOldName[] = "c:\\olddir";
char szNewName[] = "c:\\newdir";

void main (void)

   if (0 != rename(szOldName, szNewName))
      printf("Rename fails with errno = %d\n", errno);
   else
      printf("Rename is successful\n");