DOCUMENT:Q84718 17-DEC-2000 [msdos] TITLE :Redirecting a TSR May Leave File Handle Open PRODUCT :Microsoft Disk Operating System PROD/VER:MS-DOS:3.x,4.x,5.x,6.0,6.2,6.21,6.22 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft MS-DOS operating system versions 3.1, 3.2, 3.21, 3.3, 3.3a, 4.0, 4.01, 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 ------------------------------------------------------------------------------- SUMMARY ======= If you run a terminate-and-stay-resident (TSR) program and redirect the output to a file using a command similar to TSR > file the file handle of the redirected file is not closed automatically by MS-DOS. In this case, you can run out of file handles if the TSR reinstalls itself each time it is invoked. MORE INFORMATION ================ When a program is executed, it inherits all the files its "parent" (usually COMMAND.COM) had open. At a minimum, this usually includes the file handles for the standard devices: STDIN, STDOUT, STDAUX, STDERR, and STDPRN. If the input or output of a program is redirected, MS-DOS opens the specified file(s) and redirects STDIN or STDOUT to the file specified before executing the program. The program will input and output information as normal, but anything read from STDIN or written to STDOUT will actually go to the specified file instead. The program is not aware of this redirection (and if the program does not use STDIN or STDOUT, the redirection will appear "fail"). When the program exits, MS-DOS automatically closes the handles that were opened due to redirection. TSR programs stay resident instead of exiting, thus the redirected files are not closed automatically by MS-DOS. If MS-DOS closed file handles when a program terminates but stays resident, problems could occur if the TSR tried to use the file(s) at a later time. TSR programs can avoid this problem by closing file handle(s) when the TSR program is finished using them. For example, if the program has sent all its startup information to STDOUT and will not be using STDOUT in the future, the program can close STDOUT before terminating. If the program has read all necessary input from STDIN, close STDIN. Additional query words: 6.22 2.00 2.10 2.11 3.00 3.10 3.20 3.21 3.30 3.30a 4.00 4.00a 4.01 4.01a 5.00 5.00a 6.00 6.20 ====================================================================== Keywords : Technology : kbMSDOSSearch kbMSDOS321 kbMSDOS400 kbMSDOS320 kbMSDOS330a kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS310 kbMSDOS500 kbMSDOS330 kbMSDOS401 kbMSDOS500a Version : MS-DOS:3.x,4.x,5.x,6.0,6.2,6.21,6.22 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2000.