How to set BCDEdit in C++ code

天张 1

I want to set BCDEdit \set increaseuserva 3072 in my c++ desktop application.
I try to use system() function to set, but it's not work.

3 answers

Castorix31 83,206 Reputation points

2022-09-27T15:52:45.387+00:00
This works for me (x86 on Windows 10 21H1) :

BOOL bWow64 = false; IsWow64Process(GetCurrentProcess(), &bWow64); if (bWow64) { PVOID OldValue = NULL; if (Wow64DisableWow64FsRedirection(&OldValue)) { //... } } ShellExecute(0, L"runas", L"BCDEdit.exe", L"/set increaseuserva 3072", NULL, SW_SHOWNORMAL);
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3 people found this answer helpful.
RLWA32 43,306 Reputation points

2022-09-27T16:11:28.713+00:00

Oh well, instead of providing a cut and paste solution I was hoping that the questioner would learn from the process. Anyway, ...

天张 1 Reputation point

2022-09-28T07:52:41.493+00:00

Anyway, Thanks for your help!

天张 1 Reputation point

2022-09-28T07:55:16.893+00:00

Thanks for your solution, I will try it!

天张 1 Reputation point

2022-09-28T08:02:54.383+00:00

That code means x86 program will disable the File Redirection mechanism, am I right?

Castorix31 83,206 Reputation points

2022-09-28T08:10:21.63+00:00

Yes, otherwise BCDEdit won't be found with a 32-bit app

天张 1 Reputation point

2022-09-28T11:38:58.823+00:00

the code works for me. Thank you so much!

RLWA32 43,306 Reputation points

2022-09-28T11:47:11.243+00:00

Don't forget to re-enable File System redirection by calling the Wow64RevertWow64FsRedirection function. :)

天张 1 Reputation point

2022-09-28T12:17:35.06+00:00

I have the other problem. ShellExecute() must show a admin permission requesting UI, I want my application user do not feel that
I try to use system("BCDEdit /set increaseuserva 3072"); But it only work when my app is run with admin mode.
Can system() execute bcdedit in admin? Is there any solution?

天张 1 Reputation point

2022-09-28T12:20:14.827+00:00

Got it！
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RLWA32 43,306 Reputation points

2022-09-27T08:39:26.073+00:00

BCDEdit requires administrator privileges. So your application must be running "as Administrator".

Before doing this I suggest you carefully read https://learn.microsoft.com/en-us/windows-hardware/drivers/devtest/bcdedit--set#memory-related-settings and also 4-gigabyte-tuning. Do you have a very good reason for changing this setting? Make sure you have a good system backup available.
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2 people found this answer helpful.
天张 1 Reputation point

2022-09-27T09:31:37.357+00:00

Thanks for your reply.
I have read the doc before, my 32-bit app always OOM due to less of virtual memory, so I try to use 4GB to resolve low virtual memory.

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I try to build a release demo and run with admin mode, but it still not woking.
the code like this ' ShellExecute(hWnd, L"bcdedit", L"/set increaseuserva 3072", NULL, NULL, 0);'
is there something wrong?

RLWA32 43,306 Reputation points

2022-09-27T09:45:41.127+00:00

Are you using a 32-bit version of Windows?

Did you notice this important guidance -- "On 64-bit editions of Windows, 32-bit applications marked with the IMAGE_FILE_LARGE_ADDRESS_AWARE flag have 4 GB of address space available."

天张 1 Reputation point

2022-09-27T09:49:11.493+00:00

Yeah, I know the link param IMAGE_FILE_LARGE_ADDRESS_AWARE.
My question is 'I want to set bcdedit in c++ code', if I use command line to 'set bcdedit' in cmd, it is work fine.

RLWA32 43,306 Reputation points

2022-09-27T09:51:09.343+00:00

Your call to ShellExecute is wrong. You need to pass the verb "runas" to request elevation.

天张 1 Reputation point

2022-09-27T10:08:58.377+00:00

My question is similar with https://stackoverflow.com/questions/47900900/systembcdedit-set-safeboot-does-not-set-windows-to-safeboot.

I can set increaseuserva in command line successfully. but when I call system() or ShellExecute() in program, it's not work.(in admin mode)

天张 1 Reputation point

2022-09-27T10:11:32.95+00:00

could you give me an example? I am a c++ noob. Thanks a lot

RLWA32 43,306 Reputation points

2022-09-27T10:31:04.59+00:00

ShellExecute(hwnd, "runas", "C:\\Windows\\System32\\cmd.exe", "/K dir", "C:\\Windows\\System32", SW_SHOW);

Above will open an elevated command prompt and list the contents of the System32 folder.

RLWA32 43,306 Reputation points

2022-09-27T14:39:19.787+00:00

You must build your application as a 64-bit application. It sounds like you are creating a 32-bit application. The bcdedit.exe program does not exist in the SySWOW64 folder which is referenced by a 32-bit process due to File System Redirection.

By the way, just saying that something is not working doesn't give any information to help diagnose the problem For example, when you call ShellExecute to run bcdedit.exe as an administrator what value does the ShellExecute return?

天张 1 Reputation point

2022-09-28T07:50:26.71+00:00

Yes, I gonna ask the same question too.
I am creating a 32-bit app, it cannot access C:/Windows/system32/bcdedit.exe

天张 1 Reputation point

2022-09-28T08:01:24.013+00:00

I will learn the mechanism about File System Redirection

RLWA32 43,306 Reputation points

2022-09-28T08:07:57.733+00:00

I will learn the mechanism about File System Redirection

That's good to hear. Here's a tip from the documentation at https://learn.microsoft.com/en-us/windows/win32/winprog64/file-system-redirector

"32-bit applications can access the native system directory by substituting %windir%\Sysnative for %windir%\System32. WOW64 recognizes Sysnative as a special alias used to indicate that the file system should not redirect the access. This mechanism is flexible and easy to use, therefore, it is the recommended mechanism to bypass file system redirection. Note that 64-bit applications cannot use the Sysnative alias as it is a virtual directory not a real one."

天张 1 Reputation point

2022-09-28T09:12:23.777+00:00

OK，Thank you！
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Limitless Technology 44,121 Reputation points

2022-09-30T07:45:27.893+00:00

Hi,

Thank you for your question and reaching out.

I understand that you're having issues running the bcedit command in your desktop. Have you tried running manually opening Command Prompt in administrative mode? To do so, here are the commands:

c:\WINDOWS\system32>bcdedit /set safeboot network
c:\WINDOWS\system32>shutdown -r -f -t 0

Then try running the BCEDIT command again.

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How to set BCDEdit in C++ code

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