Using REG to add a variable to User variable Path

Question

Using REG to add a variable to User variable Path

sValentin 81

I want to use REG to add a value to User variable Path (not System path) that in the future may have to be linked to a new folder, and for that reason I'm also adding a User variable ("MyVariable" for this example) which in the future if needed will be changed to a new folder. This way will be easier then removing the old value from Path and adding the new one. But the problem that I have is that when I run the following command it will copy the values from System variable Path and then add the value that I want to User variable Path, and it doesn't copy the values from User variable Path that I was thinking it will do. The reason for adding the values is that the program that I'm creating needs to have a folder in User or System Path, and as User doesn't need administrator rights, I'm using that one. What do I need to change so that it will just add the value that I want to User variable Path and stop it from copying the values from System Path?

reg add "HKEY_CURRENT_USER\Environment" /v PATH /t REG_EXPAND_SZ /d "%path%;%MyVariable%\folder\location" /f

//Edit: I ended up switching to use RegOpenKeyExA, RegQueryValueExA, RegCreateKeyEx, RegSetValueExA, and I used SendNotifyMessage(HWND_BROADCAST, WM_SETTINGCHANGE, 0, (LPARAM)TEXT("Environment")); to get past the need for a system restart/logout.

Junjie Zhu - MSFT 21,646 Reputation points

2022-07-14T03:16:44.267+00:00

Hi, Welcome to Microsoft Q&A! what is your windows system version?

2 answers

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Junjie Zhu - MSFT 21,646 Reputation points

2022-07-14T03:16:44.267+00:00

Hi, Welcome to Microsoft Q&A! what is your windows system version?

Answer 1

Castorix31 90,681

Changing User or System Environment variables is done via registry + WM_SETTINGCHANGE,

like :

                    HKEY hKey;  
                    DWORD dwResult = 0;  
                    LONG nResult = RegCreateKeyEx(HKEY_CURRENT_USER, TEXT("Environment"), 0, NULL, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, NULL, &hKey, &dwResult);  
                    if (nResult == ERROR_SUCCESS)  
                    {  
                        TCHAR wsValue[] = TEXT("Test");  
                        RegSetValueEx(hKey, TEXT("MyVariable"), 0, REG_SZ, (LPBYTE)wsValue, (_tcslen(wsValue) + 1) * sizeof(TCHAR));  
                    }  
                    if (hKey)  
                        RegCloseKey(hKey);  
                    SendNotifyMessage(HWND_BROADCAST, WM_SETTINGCHANGE, 0, (LPARAM)TEXT("Environment"));

sValentin 81 Reputation points

2022-07-13T10:19:13.18+00:00

I have to use CMD as I can't include Windows.h in the project. The software I'm using can be used for different platforms, and Windows.h isn't allowed to be added.
Castorix31 90,681 Reputation points

2022-07-13T10:21:34.447+00:00

Then why did you set the windows-api tag ?
sValentin 81 Reputation points

2022-07-13T10:24:37.767+00:00

Because it will be used only on Windows, I'm not going to offer support for the other platforms. And a simple "registry" tag wasn't there.
sValentin 81 Reputation points

2022-07-13T12:32:08.833+00:00

Also, this code is setting a User variable, which I didn't had a problem. The problem was with setting a value in User Path, as the code I wrote was using the values from System Path instead of User Path and adding a value to that. I might be able to change something to allow Windows.h, but this won't answer the question.
RLWA32 49,536 Reputation points

2022-07-13T12:42:38.493+00:00

I suggest you advise the community what technology you are allowed to use to craft a solution. For example, what about powershell? Other scripting technologies like VB script or JavaScript? That will help focus responses to your question and save time for all involved.

sValentin 81

At first I was running that with following function using CMD, but now I changed something so that I can use winreg too.

std::string executeCMD(const char* cmd) {  
	std::string result;  
	std::array<char, 128> buffer;  
	std::unique_ptr<FILE, decltype(&_pclose)> pipe(_popen(cmd, "r"), _pclose);  
	if (!pipe) {  
		return "ErrorCMD";  
	}  
	while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {  
		result += buffer.data();  
	}  
	return result;  
}

Castorix31 90,681 Reputation points

2022-07-13T13:17:41.047+00:00

It was just a random sample to show the method (to add a variable to the path, you just read "Path" value then you concatenate your string before re-writing it...)
But can't you use macros, like #ifdef _WIN32 ?
sValentin 81 Reputation points

2022-07-14T09:00:17.07+00:00

I managed to change something so that I can use Windows.h and get a working version with getting the values and adding the new one to them using winreg, so if you add an answer that gets the old values from User Path, and adds the new one, I'll accept it as the answer to the question. I used RegOpenKeyExA, RegQueryValueExA, RegCreateKeyEx, RegSetValueExA.

Answer 2

RLWA32 49,536

Use the following commands in a batch file. The batch file will create the user environment variable and the desired path string. A logout/login is needed to see the effect of the changes.

for /f "usebackq tokens=3" %%i in (`reg.exe query HKCU\Environment /v Path`) do set oldpath=%%i  
reg add HKCU\Environment /v MyVariable /t REG_SZ /d TestFolder /f  
reg add HKCU\Environment /v Path /t REG_EXPAND_SZ /d %oldpath%;^%%MyVariable^%%\folder\location /f

sValentin 81 Reputation points

2022-07-14T06:04:21.597+00:00

Is the need for restart/logout from using REG ADD? If I switch to winreg, will that go away and work without having to restart/logout? I have the same problem with the code that I came up with. The variable is added fine, but I have to restart the computer (haven't thought to try a logout) in order to use it.
RLWA32 49,536 Reputation points

2022-07-14T07:21:19.267+00:00

If I switch to winreg, will that go away and work without having to restart/logout?

I'm not familiar with "winreg". What is it?
sValentin 81 Reputation points

2022-07-14T07:27:46.787+00:00

You can use that as C++ code for registry functions, I did a test, and even by using that I still have to restart/logout.
Castorix31 90,681 Reputation points

2022-07-14T07:31:38.89+00:00

That's why WM_SETTINGCHANGE, is used in C++...
RLWA32 49,536 Reputation points

2022-07-14T07:31:59.217+00:00

To avoid logout/login you need to broadcast the WM_SETTINGCHANGE message using the Windows API to notify the system that you have made the change. This was mentioned in the response from @Castorix31 .
sValentin 81 Reputation points

2022-07-14T07:42:11.307+00:00

I'll give that a try, but without saying what it does, and only giving some code, some won't know what it was used for, like my case. I'm not a C++ programmer, but I have to use it in order to use JNI.

SendNotifyMessageA "Sends the specified message to a window or windows." I thought is is for when you launch the app using another one, and it is waiting for a response (closed when finished, closed prematurely), and in my case I don't care about that response, so I ignored it.
RLWA32 49,536 Reputation points

2022-07-14T07:50:23.967+00:00

Read wm-settingchange
sValentin 81 Reputation points

2022-07-14T07:59:28.223+00:00

To avoid logout/login you need to broadcast the WM_SETTINGCHANGE message using the Windows API to notify the system that you have made the change.

After reading your explanation I did go and looked that up, but what it was initially said "Changing User or System Environment variables is done via registry + WM_SETTINGCHANGE," and seeing in what function it was used it (and what the function says it does), it can lead to misunderstanding. So as a suggestion, adding a little explanation about what the line of code does, it helps a lot. Yeah you may see it as giving/helping too much, but not everyone has the same bag of knowledge, or understands the same way, in which case an explanation really does helps a lot.
RLWA32 49,536 Reputation points

2022-07-14T08:18:02.58+00:00

After reading your explanation I did go and looked that up, but what it was initially said "Changing User or System Environment variables is done via registry + WM_SETTINGCHANGE,"

By the way, that wasn't my response. I did explain the purpose of broadcasting the message to notify the system of the change.

We do assume some base level of knowledge about programming and Windows when responding to questions. If we didn't, every response would be extraordinarily cumbersome. Its up to the questioner to advise the limitations of their knowledge and experience.

And, the actual question you asked about how to use reg.exe has been answered.
sValentin 81 Reputation points

2022-07-14T08:35:11.05+00:00

If we didn't, every response would be extraordinarily cumbersome. Its up to the questioner to advise the limitations of their knowledge and experience.

Yeah, I see your point, but at the same time when I (and others reading posts on different websites, not just here) actually said my level of understanding the answers were kinda harmful, in the sense that the answer was in the form of "Here go and read this book on the basics and then come back" when saying it's just starting learning and has "this" problem, or other forms that were speaking in a really broad way and having to go and read lots of stuff that don't have anything to do with the question case, and have even more questions then when you started, and getting to a point where I know people that quit programming because of cases like that, when the person asking the question wanted just an answer to that particularly case, and not how C++ is working.

Like you don't need to know how 1+1 works, to know the answer is 2. The reason for 1+1=2 mathematically is really complicated if you go deep in it. As it is with C++, you can do A LOT with it (and other languages), but we don't need that "A LOT", only a use case of it.

I don't want to generalize this, because I know there are lots of people who simply want to help others, but there are a few bad apples, and those lead to really unfortunately situations.
RLWA32 49,536 Reputation points

2022-07-14T08:51:36.61+00:00

I think you'll find that the Q&A site is more "user friendly" than some others you may have visited. For example, there is no down-voting of questions or responses.

Many of the folks who answer questions here are not Microsoft employees. We share our time, knowledge and experience without compensation. So please factor that into your consideration of responses you have received.

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Using REG to add a variable to User variable Path

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