FIX: The offset that is generated to access a structure member or a class member is incorrect when you compile an application by using the /Ox option or the /O2 option in Visual Studio 2008 SP1

Symptoms

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)

Resolution

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:

http://support.microsoft.com/contactus/?ws=supportNote 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.

Prerequisites

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	Date	Time	Platform
C2.dll	15.0.30729. 4082	2,283,320	19-Mar- 2009	05:13	x86
C2.dll	15.0.30729.4082	2,36 1,656	19-Mar- 2009	05:13	x86
C2.dll	15.0.30729.4082	3,01 7,528	19-Mar- 2009	05:13	x64
Link.exe	9.0.30729.4082	1,0 54,520	19-Mar- 2009	05:13	x64
Link.exe	9.0.30729.4082	799 ,032	19-Mar-2009	05:13	x86

Workaround

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.

Status

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

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;
}

Compile the application by using the following command:

cl test.cpp /O2 /MD

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