PRB: File Routines Fail with Some File Names (CON, PRN, AUX, CLOCK$, NUL, COM1 - COM9, LPT1 - LPT9)

ID: Q216654

The information in this article applies to:

Microsoft Windows NT, versions 3.5, 3.51, 4.0
Microsoft Windows versions 95, 98
Microsoft Windows 2000

SYMPTOMS

File creation, deletion, read, write, and manipulation routines fail or behave unpredictably when dealing with a file with one of the following names: CON, PRN, AUX, CLOCK$, NUL, COM1 - COM9, LPT1 - LPT9. To illustrate this, start a command prompt under Windows 9x or Windows NT. Copy any file to an unused name; for example, Testfile.tmp. Now, type in the command REN testfile.tmp CON.

RESULTS: You get an error that states the file already exists.

CAUSE

This problem is caused by name collision with the reserved device names. These names are reserved by Windows 95, Windows 98, Windows NT, and Windows 2000 for backwards compatibility with MS-DOS, which reserved these names for various devices. If these device names were not reserved, one could no longer use the following standard MS-DOS syntax (from a command prompt) to create a text file:


COPY CON testfile.txt

or the following method to view it:


COPY testfile.txt CON

or the following method to print it:


COPY testfile.txt PRN

or the following method to output text typed from the keyboard to the printer:


COPY CON PRN

RESOLUTION

These names must be avoided when creating file names.

STATUS

This behavior is by design, for backwards compatibility with MS-DOS applications, and is a consequence of the MS-DOS device driver architecture. Because legacy MS-DOS applications, or MS-DOS applications ported to console-mode applications, may explicitly use these reserved file names, these file names must be retained as long as MS-DOS backwards compatibility is required in the Windows family.

MORE INFORMATION

Similar behavior may be observed if special legacy-type device drivers that register other reserved names are loaded (for example, by Config.sys or Autoexec.bat).

REFERENCES

For additional information, please see the following article in the Microsoft Knowledge Base:

Q120716 How To Remove Files with Reserved Names in Windows NT

Additional query words: CON PRN AUX CLOCK$ NUL COM1 COM2 COM3 COM4 LPT1 LPT2 LPT3


Keywords          : kbKernBase kbNTOS350 kbNTOS351 kbNTOS400 kbWinOS95 kbWinOS98 
Version           : WINDOWS:95,98; winnt:3.5,3.51,4.0; :
Platform          : WINDOWS winnt 
Issue type        : kbprb

Last Reviewed: April 3, 1999