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The Fc.exe command does not work correctly on a Windows XP-based computer when the two files that you are comparing have the TAB or SPACE character around the 128th byte in a string of characters

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On a Windows XP-based computer, you use the Fc.exe command to compare two files. However, if the two files have the TAB character or the SPACE character anywhere in the 7 bytes that come before the 128th byte in a string of characters, the Fc.exe command does not work correctly.
Currently, the Fc.exe command reads 127 bytes in a string of characters at one time. By default, the Fc.exe command expands the TAB character into spaces before the command compares two files that contain the TAB character. The command may expand the TAB character into as many as 8 spaces, depending on where the TAB character is located in the string. For example, if the TAB character occurs at index 120, 121, 122, 123, 124, 125, or 126, the TAB character should be expanded to 7 spaces, 6 spaces, 5 spaces, 4 spaces, 3 spaces, 2 spaces, or 1 space, respectively. However, this behavior causes the Fc.exe command to work incorrectly.
After you apply this hotfix, the Fc.exe command will read 128 bytes every time that it runs. Because 128 is multiple of 8, this resolves the problem.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.


To apply this hotfix, you must have Windows XP Service Pack 2 (SP2) or a later service pack installed. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
322389 How to obtain the latest Windows XP service pack

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.
Windows XP with Service Pack 2, x86-based versions
File nameFile versionFile sizeDateTimePlatform
Windows XP with Service Pack 3, x86-based versions
File nameFile versionFile sizeDateTimePlatform
To work around this problem, run the Fc.exe command together with the /b (binary) switch.

Note Binary mode does not show the location of the differences between the two files.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
More information
Fc.exe is a command that compares two files or two sets of files and then displays the differences between them.

Article ID: 953930 - Last Review: 01/16/2015 10:22:03 - Revision: 2.0

Microsoft Windows XP Home Edition, Microsoft Windows XP Professional

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