Q62663: PRB: CodeView May Appear to Hang on gets() If Screen Swap Is Off

Article: Q62663
Product(s): Microsoft Programming Utilities
Version(s): 3.0,3.11,3.12,3.14,3.5,4.0,4.01,4.05,4.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 26-JUN-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft CodeView for MS-DOS, versions 3.0, 3.11, 3.14, 4.0, 4.01, 4.05, 4.1 
- Microsoft CodeView for OS/2, versions 3.0, 3.11, 3.12, 3.5 
-------------------------------------------------------------------------------

SYMPTOMS
========

The Microsoft CodeView Debugger will appear to hang when you step or execute
past a call to the gets() run-time routine if the Screen Swap option is turned
off.

CAUSE
=====

The apparent lock-up results because the gets() call causes focus to shift to
the debuggee's screen and there is no way for CodeView to get to that screen
with Screen Swap off.

Since in MS-DOS, the debuggee's screen still displays CodeView, you may be able
to type in the information and press Return to continue. This will temporarily
display the debuggee's input over CodeView's screen. A better method in MS-DOS
is to break execution with CTRL+C so that you may turn swapping back on.

RESOLUTION
==========

To get past this deadlock with CVP under OS/2, manually switch screen groups to
the one labeled "CVP app appname.EXE". Once there, you can provide a response to
the waiting gets() call. After entering a string, you can switch back to the
screen group running CVP and continue debugging.

MORE INFORMATION
================

The sample code below illustrates this situation. Compile the code as indicated
and bring up the .EXE in CodeView. Select the Option menu and turn off Screen
Swap if it is on. Next, step past the gets() call. In MS-DOS, you will need to
press CTRL+C to regain control. In OS/2, you will need to switch screen groups
to provide the necessary input to the program.

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

  /* Compile options needed: /Zi /Od
  */ 

  #include <stdio.h>

  char string[256];

  void main (void)
  {
      printf ( "Enter a string: ") ;
      gets ( string ) ;
      printf ( "Echoing : %s\n", string) ;
  }

Additional query words: 3.00 3.50 4.00 4.10

======================================================================
Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbCodeView kbZNotKeyword3 kbCodeView300DOS kbCodeView311DOS kbCodeView314DOS kbCodeView400DOS kbCodeView401DOS kbCodeView405DOS kbCodeView410DOS kbCodeView300OS2 kbCodeView311OS2 kbCodeView312OS2 kbCodeView350OS2
Version           : :3.0,3.11,3.12,3.14,3.5,4.0,4.01,4.05,4.1

=============================================================================

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 1986-2002.