Article ID: 217033 - Last Review: September 7, 2005 - Revision: 3.0

FIX: Code compiled with the /Og option in Visual C++ 6.0 can cause incorrect calculation for doubles

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This article was previously published under Q217033

SYMPTOMS

Code compiled with the /Og option can cause incorrect calculation for doubles. In some cases, it loads only half of a double's bytes into memory causing incorrect results in later calculations.

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Disable global optimizations.

Global optimizations can be disabled for the entire project or for a particular source file by removing /Og from either the project's release build compiler settings or an individual file's release build compiler settings.

Note /O1 (minimize size) and /O2 (maximize speed) are composite switches that include /Og. If you are using /O1 or /O2 disable global optimizations by adding /Og- to the appropriate compiler settings.

Global optimization can also be disabled on a function by function basis through the use of #pragma optimize as follows.

#ifndef _DEBUG  // current build is not a debug build<BR/>
#pragma optimize("g", off) // disable global optimization<BR/>
#endif // _DEBUG<BR/><BR/>
void SomeFunction()<BR/>

*** Body of SomeFunction Here ***
return;

#ifndef _DEBUG // current build is not a debug build<BR/>
#pragma optimize("g", on) // re-enable global optimization<BR/>
#endif // _DEBUG<BR/>

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section.

This bug was corrected in Visual Studio 6.0 Service Pack 3. For more information about Visual Studio service packs, click the following article numbers to view the articles in the Microsoft Knowledge Base:

194022 (http://support.microsoft.com/kb/194022/ ) Visual Studio 6.0 service packs, what, where, why

194295 (http://support.microsoft.com/kb/194295/ ) How to tell that a Visual Studio service pack is installed

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