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Microsoft KB Archive/100773

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Knowledge Base


The developer studio integrated debugger may display incorrect values for the local variables in an application when the application is compiled with optimizations on

Article ID: 100773

Article Last Modified on 12/9/2005



APPLIES TO

  • Microsoft Visual C++ 1.0 Professional Edition
  • Microsoft Visual C++ 2.0 Professional Edition
  • Microsoft Visual C++ 4.0 Standard Edition
  • Microsoft Visual C++ 5.0 Enterprise Edition
  • Microsoft Visual C++ 6.0 Enterprise Edition
  • Microsoft Visual C++ 5.0 Professional Edition
  • Microsoft Visual C++ 6.0 Professional Edition
  • Microsoft Visual C++ 6.0 Standard Edition
  • Microsoft Visual C++ .NET 2002 Standard Edition
  • Microsoft Visual C++ .NET 2003 Standard Edition
  • Microsoft Visual C++ 2005 Express Edition



This article was previously published under Q100773


SYMPTOMS

The Developer Studio integrated debugger may display incorrect values for the local variables in an application. This can occur when the application being debugged was compiled with optimizations on.

RESOLUTION

During the debugging process for your application, specify the /Od compiler option switch to disable optimizations.

MORE INFORMATION

The C/C++ compilers mentioned above make ample use of registers to store local variables. This is particularly true when optimizations are turned on. Therefore, information regarding local variable storage is not always available to the debugger.

The following code example demonstrates this behavior. If you compile this code with optimizations disabled (specify the /Od compiler option switch), the values of the local variables in the func1() function are correctly displayed after the code calls the func2() function. However, if you compile the code with optimizations (specify the /Ox compiler option switch), the values of the same local variables do not display correctly until the code executes the return statement from func2().

Sample Code

   /*
    * Compile options needed: /Ox
    */ 

   void func2(int *arg1, int *arg2, int *arg3)
   {
      *arg1 = *arg2 = *arg3 = 5;
   }

   int func1(int arg1)
   {
      int local1, local2;

      func2(&arg1, &local1, &local2);

      return arg1 + local1 + local2;

   }

   void main(void)
   {
      func1(1);
   }
                


Additional query words: vwbdebug vcnt

Keywords: kbide kbdebug kbprb KB100773