Setting path environment variable

I have made some code to change the path environment variable, but it doesn't seem to be working. Somehow. I know that there are current user and system env vars, but I don't know which I am setting. I change it, all functions are successful, but when it is done, I can not access the things in the path in the command prompt.

Code:

	std::vector<TCHAR> v;
	int ret = 0;

	ret = ::GetEnvironmentVariable
		(TEXT("PATH"), 0, 0);

	if(ret)
	{
		v.resize(ret);
	}

	ret = ::GetEnvironmentVariable
		(TEXT("PATH"), &v[0], v.size());

	if(ret)
	{
		std::tstring t(&v[0]);

		t += TEXT(";C:\\Program Files\\MinGWStudio\\MinGW\\bin");

		std::tcout << t;

		ret = ::SetEnvironmentVariable(TEXT("PATH"), t.c_str());
	}

Definitely um, yeah, doesn't work. Confusing.

Enviroment variables inherit only one-way, from parent to child.
Any change you make to a childs enviroment works on a copy of the environment only.

What about system environment variables, like path. I don't have spawned processes or anything.

Same thing.

If you spawn a process from what you've done, you'll see the local changes you've made.

Sorry. I guess I'm not trying to make local changes, but rather global ones. Is that possible with these API's?

Edit: I'm dumb.

Calling SetEnvironmentVariable has no effect on the system environment variables. The user can add or modify system environment variables using the Control Panel. To programmatically add or modify system environment variables, add them to the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Contro l\Session Manager\Environment registry key, then broadcast a WM_SETTINGCHANGE message with lParam set to the string "Environment". This allows applications, such as the shell, to pick up your updates. Note that the values of the environment variables listed in this key are limited to 1024 characters.

So uh, yeah. I'm doing this now:

Code:

	LONG ret;
	HKEY hkey;

	ret = ::RegOpenKeyEx(HKEY_LOCAL_MACHINE, TEXT("SYSTEM\\CurrentControlSet\\Control\\ \
			Session Manager\\Environment"), 0, KEY_ALL_ACCESS, &hkey);

	if(ret != ERROR_SUCCESS)
		std::tcout << ::GetLastError();

It is never ERROR_SUCCESS, and GetLastError is always 0. Yah.