Article: Q135526
Product(s): Microsoft C Compiler
Version(s): 1.0,1.5,1.51,1.52,2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
Operating System(s):
Keyword(s): kbCodeGen kbCompiler kbCPPonly kbVC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410
Last Modified: 11-FEB-2002
-------------------------------------------------------------------------------
The information in this article applies to:
- Microsoft Visual C++, versions 1.0, 1.5, 1.51, 1.52, 2.0, 2.1, 2.2, 4.0, 4.1
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 5.0, 6.0
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 5.0, 6.0
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0
-------------------------------------------------------------------------------
SYMPTOMS
========
Invalid results may be generated under these conditions:
- Your code defines an inline function that uses global or static data, and it
invokes that function twice within an expression.
- You are using the /Ob1 or /Ob2 or /Ox compiler optimization switch with the
32-bit compiler, or you are using the /Ob1g or /Ob2g or /Ox switch with the
16-bit compiler.
- The global or static variable appears in the return expression for the
function.
RESOLUTION
==========
Do not use the above optimizations.
-or-
Assign the return value of one of the function calls to a local variable. Then
use the local variable in the expression.
STATUS
======
Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.
This problem was corrected in Microsoft Visual C++ .NET.
MORE INFORMATION
================
Sample Code to Reproduce the Problem
------------------------------------
/* Compile options needed 32-bit Compiler: /Ob1, or /Ob2, or /Ox
/* Compile options needed 16-bit Compiler: /Ob1g, or /Ob2g, or /Ox
*/
#include <stdio.h>
int nGlobal = 0;
inline int test(int nIn) {
return nGlobal = nIn;
}
void main() {
// This will incorrectly evaluate to true.
if (test(1) == test(2))
printf("test(1) == test(2)\n");
else
printf("test(1) != test(2)\n");
// This will correctly evaluate to false.
int n = test(2);
if (test(1) == n)
printf("test(1) == test(2)\n");
else
printf("test(1) != test(2)\n");
}
Additional query words: kbVC400bug 8.00c 9.00 9.10 10.00 10.10 10.20
======================================================================
Keywords : kbCodeGen kbCompiler kbCPPonly kbVC kbVC200bug kbVC210bug kbVC220bug kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600bug kbNoUpdate
Technology : kbVCsearch kbVC400 kbAudDeveloper kbvc150 kbvc100 kbVC220 kbVC410 kbVC420 kbVC500 kbVC600 kbVC151 kbVC200 kbVC210 kbVC32bitSearch kbVC152 kbVC500Search
Version : :1.0,1.5,1.51,1.52,2.0,2.1,2.2,4.0,4.1,4.2,5.0,6.0
Issue type : kbbug
Solution Type : kbfix
=============================================================================