Microsoft KB Archive/247203

Knowledge Base

FIX: Try/Catch Block May Fail when Global Optimizations (/Og) Are Enabled

Article ID: 247203

Article Last Modified on 1/22/2004

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APPLIES TO

• Microsoft Visual C++ 6.0 Enterprise Edition
• Microsoft Visual C++ 6.0 Professional Edition
• Microsoft Visual C++ 6.0 Standard Edition

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This article was previously published under Q247203

SYMPTOMS

When trying to build an application that uses C++ exception handling, with global optimizations enabled, the catch handler within the try/catch block may not catch any of the exceptions that are thrown by the instructions in the try block. See the "More Information" section below for details.

CAUSE

The optimizer optimizes the try/catch block incorrectly.

RESOLUTION

Here are the two ways to work around this problem:

1. Disable global optimizations on a function-by-function basis using the optimize pragma with the "g" option. /Og- disables global optimization on a file-by-file basis.
2. Use the asynchronous exception handling model by specifying the /EHa compiler option.

STATUS

This bug was corrected in Microsoft Visual C++ .NET 2002.

MORE INFORMATION

Steps to Reproduce Behavior

Compile Options : cl /GX /GR /Og test.cpp

//test.cpp
#include <iostream>
using namespace std;

class CObject
{
    virtual function() {};  //necessary to make the class polymorphic
};


class B : public CObject
{
public:
    CObject* m_pComp;
    void Test() const;
};

void B::Test() const
{
    B* pComp;
    try
    {
        pComp=dynamic_cast<B*>(m_pComp);
    }
    catch(exception& exc)   //The exception is caught only if Global Optimizations are disabled.
    {
        cout << "In Catch Block\n";
        cout << "Exception Caught\n" <<endl;
    }
}

void main()
{
    B object;   //m_pComp is intentionally not initialized so that the exception occurs.
    object.Test();
}

Expected Output:
In Catch Block
Exception Caught

                

When the above code is compiled using /Og, then the control never enters the catch block and results in an access violation.

Keywords: kbbug kbpending KB247203

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