Q153005: PRB: Longjmp Inside a _try Block Fails on PowerPC

Article: Q153005
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kbVC kbHWPowerPC
Last Modified: 04-AUG-2001

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The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - *EDITOR Please do not choose this product*Microsoft Visual C++ 32-bit Edition* use 241, 265, 225, version 4.1, on platform(s):
      - the hardware: PowerPC Processor 
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SYMPTOMS
========

A program that contains a longjmp called inside a _try block may not call a
_finally block. The sample code below is verified to work consistently on Alpha,
MIPS and Intel platforms. It fails only on Power PC.

WORKAROUND
==========

The solution is to include the setjmpex.h file instead of setjmp.h. The latter
provides consistent behavior on all platforms, but may cause a performance
degradation. Note: either setjmp.h or setjmpex.h may be included, but not both,
because each defines the setjmp macro in a different way.

STATUS
======

This behavior is by design.

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

The on-line documentation claims the following:

  "Exiting a try-finally statement using a return statement or the longjmp
  run-time function is considered abnormal termination. It is illegal to jump
  into a __try statement, but legal to jump out of one."

Consequently, a longjmp within a _try block should cause the _finally to be
executed.

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

     /* Compile options needed:
     */ 

     #include <stdio.h>
     #include <stdlib.h>
     //#include <setjmpex.h>  // uncomment this line for the workaround
     #include <setjmp.h> // comment this line out for the workaround
     #include <windows.h>

     CRITICAL_SECTION    cs;
     jmp_buf             jmpbuf;

     void main()
     {
          int  i = 0, j;
          int  hits = 0;

          if(setjmp(jmpbuf))
          {
               hits += 1;
               i = 0;
               printf("\n\n Jump.....\n\n");
          }

          while(1)
          {
               for(j = 0; j < 10; j++)
                    printf("%d ", i++);
               _try
               {
                    longjmp(jmpbuf, 1);
               }
               _finally
               {
                    printf("\n\nInside finally....\n");
               }
          }
     }

Additional query words:

======================================================================
Keywords          : kbVC kbHWPowerPC 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : winnt:
Issue type        : kbprb

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

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