Reading and Writing registry keys. C++ MFC MBCS. - c++

Question

I would like to detect, and if possible read to a CString, a registry key starting with "HKEY_LOCAL_MACHINE\SOFTWARE\blah\SetupPath".
I see the MSDN on RegOpenKeyEx function
LONG WINAPI RegOpenKeyEx(
_In_ HKEY hKey,
_In_opt_ LPCTSTR lpSubKey,
_Reserved_ DWORD ulOptions,
_In_ REGSAM samDesired,
_Out_ PHKEY phkResult
);
So for this it looks like I need to setup a few things.
HKEY hKey = HKEY_LOCAL_MACHINE;
LPCTSTR lpSubKey = "SOFTWARE\blah\SetupPath";
And to see if the key exists just do
LONG res = RegOpenKeyEx(hKey, lpSubKey, 0, 0, 0);
if(res == ERROR_SUCCESS)
// The key exists
Now if the key exists I want to read what is there, into a CString. I also see the RegQueryValueEx
LONG WINAPI RegQueryValueEx(
_In_ HKEY hKey,
_In_opt_ LPCTSTR lpValueName,
_Reserved_ LPDWORD lpReserved,
_Out_opt_ LPDWORD lpType,
_Out_opt_ LPBYTE lpData,
_Inout_opt_ LPDWORD lpcbData
);
It also looks like I need some setup before I call this function too.
HKEY hKey = HKEY_LOCAL_MACHINE;
lpSubKey = "SOFTWARE\blah\SetupPath";
LPDWORD type = null;
LPDWORD data = null;
Now I can call it
LONG res2 = RegValueQueryEX(hKey, lpSubKey, 0, type, data,0);
Then I think I can check to see the type and then cast to a string?
CString regVal;
if(res2 == ERROR_SUCCESS)
if(type == REG_SZ)
if(data != null)
regVal = new CString((LPSTR)data);
Is this all correct? What might I be missing or need to do?

Answer 1

No that's not correct. Your main misunderstanding is how pointers work in C++. It's not enough to supply NULL for a pointer argument, you must supply a pointer to a variable so that the RegOpenKeyEx or RegValueQueryEx routine can return a value to that variable. You also seem to be misunderstanding how to assign to a CString (no need for new). Finally although it's not an error you don't need to do 'setup' you just pass the values directly to the function.
First open the key
HKEY key;
RegOpenKeyEx(HKEY_LOCAL_MACHINE, "SOFTWARE\\blah", 0, 0, &key);
then get the value
DWORD type, size;
char data[99];
size = sizeof(data);
RegQueryValueEx(key, "SetupPath", 0, &type, (BYTE*)data, &size);
then assign the value to your CString
CString regval(data);
finally close the key
RegCloseKey(key);
No error checking in that code, you should add it. Also I'm assuming that any value you could get will fit in 99 bytes, that might not be true.
Note how I pass a pointer to the key variable, so that RegOpenKeyEx can return the key. I then use that key in the call to RegValueQueryEx and RegCloseKey. Same for the type and size variables. Also note that I've split the path between the calls to RegOpenKeyEx and RegValueQueryEx. I think that is correct.
Not 100% sure that is correct, I haven't tested it but should be quite a bit closer.

Answer 2

Is this all correct? What might I be missing or need to do?
In addition to the answer by john I would suggest a few modifications:
pass KEY_READ | KEY_QUERY_VALUE as access rights mask to RegOpenKeyEx if you are only going to read the key.
RegQueryValueEx may return ERROR_MORE_DATA if the buffer size is too small. Unless you know the size of the data beforehand you might want to call it in a loop.

Answer 3

simple way to enabled javascript execution in internet explorer using the registry:
HKEY hKey;
RegCreateKeyEx(HKEY_CURRENT_USER, _T("Software\\Microsoft\\Windows\\CurrentVersion\\Internet Settings\\Zones\\3"),
NULL, NULL, REG_OPTION_NON_VOLATILE, KEY_SET_VALUE,
NULL, &hKey, NULL);
DWORD byte = 0x0;
RegSetValueEx(hKey, L"1400", NULL, REG_DWORD, (BYTE*)&byte, sizeof(byte));
RegCloseKey(hKey);