DOCUMENT:Q43391  25-JUL-2001  [visualc]
TITLE   :INFO: Handling Floating-Point Errors in C
PRODUCT :Microsoft C Compiler
PROD/VER:MS-DOS:6.00ax,7.0; OS/2:5.1,6.00a; WINDOWS:1.0,1.5; WINDOWS NT:1.0,2.0,4.0,4.1,5.0
OPER/SYS:
KEYWORDS:kbCRT kbVC kbVC150 kbVC200 kbVC210 kbVC220 kbVC400 kbVC410 kbVC500 kbVC600

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

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

 - The C Run-Time (CRT), included with:
    - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax 
    - Microsoft C for OS/2, versions 5.1, 6.0, 6.0a 
    - Microsoft C/C++ for MS-DOS, version 7.0 
    - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5 
    - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 2.2, 4.0, 4.1, 5.0, 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

With Microsoft C, floating-point error-handling routines may be written using
the signal() function; however, "return" should not be used to go back to the
calling process. If "return" is used, the floating-point state is left
undefined.

Instead, use the setjmp() function to save the stack environment before each
section of the calling process code that may potentially generate a
floating-point error. In the error handler, use _fpreset() to reinitialize the
floating-point package and longjmp() to return to the calling process.

WARNING: Neither the setjmp nor longjmp function is compatible with the C++
language.

The sample program on page 296 of the "Microsoft C/C++ Run-time Library
Reference" that shipped with Microsoft C/C++ version 7.0 demonstrates the use of
setjmp(), _fpreset(), and longjmp() to handle a floating-point error. The online
help also provides samples for these functions.

The function setjmp() saves the environment (bp, si, di, sp, and ds registers)
and return address in a buffer. The buffer is used by longjmp() to restore the
environment.

Additional query words:

======================================================================
Keywords          : kbCRT kbVC kbVC150 kbVC200 kbVC210 kbVC220 kbVC400 kbVC410 kbVC500 kbVC600 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : MS-DOS:6.00ax,7.0; OS/2:5.1,6.00a; WINDOWS:1.0,1.5; WINDOWS NT:1.0,2.0,4.0,4.1,5.0
Issue type        : kbinfo

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

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 2001.