Q135526: FIX: Bad Result If Call Inline Function Twice in Expression

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

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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 
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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

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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

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