CODEWITHSUNDEEP
c#cmdregistryaddition
Onelio
Onelio

Reputation: 323

What is the reason for different value after reg add from within a C# application and query the value from within a cmd window?

I have a program coded in C# that opens a cmd console and adds/modifies a registry value.

After the console outputs that the task completed, I test with reg query if the registry value really changed. There is no problem. I get value 0x1 as expected by me.

But when I query this registry from outside the current cmd window like another cmd executed by me as admin, the value is 0x0 on reg query.

How is this possible?

Here is my C# code:

string command = @"/K reg add HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock /t REG_DWORD /f /v AllowDevelopmentWithoutDevLicense /d 1";

        Process proc = Process.Start("cmd.exe", command);

Query from inside the executed cmd by the program:

reg query HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock
    AllowDevelopmentWithoutDevLicense    REG_DWORD    0x1

From outside:

reg query HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock
    AllowDevelopmentWithoutDevLicense    REG_DWORD    0x0
    AllowAllTrustedApps    REG_DWORD    0x0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock\AllowDevelopmentWithoutDevLicense
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock\AllowDevelopmentWithoutDevLicense=1

Upvotes: 3

Views: 1129

Answers (1)

Mofi
Mofi

Reputation: 49096

When a 32-bit application on a 64-bit Windows accesses the registry key

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

it is redirected by Windows registry redirector to

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\AppModelUnlock

whereby a 64-bit application really accesses

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\AppModelUnlock

The difference between the two registry paths is Wow6432Node visible by default only for 64-bit applications on Windows x64.

See the Microsoft developer article Registry Keys Affected by WOW64.

And for completeness see also:

There are 32-bit cmd.exe and reg.exe on 64-bit Windows in directory %SystemRoot%\SysWow64 being %SystemRoot%\System32 for 32-bit applications and 64-bit cmd.exe and reg.exe in %SystemRoot%\System32.

Your C# application is most likely compiled as 32-bit application and therefore calls 32-bit cmd.exe which calls 32-bit reg.exe.

You could workaround this from within the 32-bit application by calling explicitly %SystemRoot%\Sysnative\cmd.exe.

But be aware of the fact that %SystemRoot%\Sysnative does not exist on 32-bit Windows and also does not exist for 64-bit applications on 64-bit Windows. (Sysnative is a special alias, not a hard link, junction or a real folder.)

Therefore your 32-bit C# application needs first to check if %SystemRoot%\Sysnative\cmd.exe exists and use this path to edit the 64-bit registry value using 64-bit cmd and reg. But on 32-bit Windows %SystemRoot%\System32.exe\cmd.exe must be called by the 32-bit C# application. By the way: %SystemRoot% references the value of environment variable SystemRoot.

See also the answers on:

NOTE 1:

Running cmd.exe is not needed at all. It is possible to run directly on 32-bit Windows

%SystemRoot%\System32\reg.exe

or on 64-bit Windows

%SystemRoot%\Sysnative\reg.exe

from a 32-bit application.

NOTE 2:

And last but not least a C# application does not need to use reg.exe at all as .NET Framework has built-in support for accessing Windows registry - the Registry.SetValue Method. Microsoft even added some examples in an example code block.

KEY_WOW64_64KEY can be used in a 32-bit application to explicitly access always the 64-bit registry key as explained on Microsoft documentation page Accessing an Alternate Registry View.

Upvotes: 3

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