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Q43391: INFO: Handling Floating-Point Errors in C

Article: Q43391
Product(s): Microsoft C Compiler
Version(s): 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
Operating System(s): 
Keyword(s): kbCRT kbVC kbVC150 kbVC200 kbVC210 kbVC220 kbVC400 kbVC410 kbVC500 kbVC600
Last Modified: 25-JUL-2001

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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 
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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:

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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

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