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Consider the following scenario.

  • You create an application that loads a byte from a structure or from a class in Microsoft Visual Studio 2008 Service Pack 1 (SP1).

  • You turn on the /Ox optimization option or the /O2 optimization option.

  • You compile the application by using a release configuration for the x64 platform.

In this scenario, the offset that is generated to access the structure member or the class member is incorrect.

This problem occurs only when the structure size and the offset or the class size and the offset equal one of the following pairs:

  • (14,13)

  • (15,13)

  • (22,21)

  • (23,21)

  • (30,29)

  • (31,29)


Hotfix information

A supported hotfix is now available from Microsoft. However, it is intended to correct only the problem that is described in this article. Apply it only to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Visual Studio 2008 service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Customer Support Services to obtain the hotfix. For a complete list of Microsoft Customer Support Services telephone numbers and information about support costs, visit the following Microsoft Web site: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.


You must have Visual Studio 2008 Service Pack 1 installed to apply this hotfix.

Restart requirement

You do not have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

File name

File version

File size





15.0.30729. 4082


19-Mar- 2009





2,36 1,656

19-Mar- 2009





3,01 7,528

19-Mar- 2009





1,0 54,520

19-Mar- 2009





799 ,032





To work around this problem, add one or more dummy "unsigned char" members to extend the size of the structure or of the class to the smallest multiple of eight bytes. For example, extend 14 bytes to 16 bytes.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Steps to reproduce the problem

  1. Create an application that is named Test.cpp by using the following code in Visual Studio 2008 SP1:

    typedef struct DskDecimal
    unsigned char precision;
    unsigned char scaleFactor;
    unsigned short value[ 5];
    unsigned char maxPrecision;
    unsigned char maxScaleFactor;
    } DskDecimal;

    int main()
    DskDecimal decimal;
    decimal.maxScaleFactor = 4;
    DskDecimal self = decimal;
    return self.maxScaleFactor;
  2. Compile the application by using the following command:

    cl test.cpp /O2 /MD

The expected result is 4. However, the actual result is 0.

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