Microsoft KB Archive/151499

= FIX: Compiler Performs Illegal Sign Conversion Optimization =

Article ID: 151499

Article Last Modified on 10/17/2003

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APPLIES TO


 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 5.0 Professional Edition

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This article was previously published under Q151499



SYMPTOMS
When using the /Og optimization, or an option that includes it such as /Ox, /O2, or /O1, the compiler may incorrectly sign extend a value when performing a conversion.



STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97, Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why



MORE INFORMATION
The following sample demonstrates this bug. As you step through this code in the debugger, you will observed that i and j compare as equal when they should not.

Sample Code
int i, j;  char c1=-1, c2, c3; bool f {     i = c1 + (unsigned char)c1; j = c1 + c1; if( i == j ) // this should fail return false; else return true; }

Keywords: kbbug kbfix kbvs97sp1fix kbvs97sp2fix KB151499

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