Microsoft KB Archive/188721

= BUG: AV Using ios-Derived Type in Multithreaded Apps =

Article ID: 188721

Article Last Modified on 12/8/2003

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APPLIES TO

 The C Run-Time (CRT), when used with:  Microsoft Visual C++ 4.0 Standard Edition

 Microsoft Visual C++ 4.1 Subscription

 Microsoft Visual C++ 4.2 Enterprise Edition

 Microsoft Visual C++ 4.2 Professional Edition</li></ul>

 Microsoft Visual C++ 5.0 Enterprise Edition</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul>

 Microsoft Visual C++ .NET 2002 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q188721

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SYMPTOMS
When you create and destroy ios-derived classes in multiple threads, an access violation can occur.

This only occurs when you use the old iostream library rather than the Standard C++ Library introduced in Visual C++ 5.0. You can access the old iostream library by including iostream header files with a .h extension, such as iostream.h or strstrea.h. The new header files do not have an extension, such as iostream or strstream.

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CAUSE
A static member ios::fLockcInit is used to hold reference counts for a critical section used in the multi-threaded C Run-Time Library to provide synchronization for the ios class. Ios::fLockcInit is modified without synchronization during construction and destruction of ios thereby allowing a race condition. The critical section reference counted by ios::fLockcInit may be destroyed more than once or used after it is destroyed.

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RESOLUTION
For Visual C++ 5.0, use the Standard C++ Library instead of the old iostream library.

For earlier versions of Visual C++, either do not use ios-derived classes or provide synchronization in the CRT and rebuild it. If you rebuild the CRT, you may not redistribute a DLL named the same as the DLLs Microsoft ships; you must give the DLL a different name. Microsoft does not support modified CRTs.

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STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

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MORE INFORMATION
ios-derived classes include: iostream, istream, ostream, fstream, ifstream, ofstream, strstream, istrstream.

Additional query words: kbCRT kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbDSupport kbdss

Keywords: kbbug kbpending KB188721

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