Set Registry Value to a Wide Character String (WCHAR) in C++ - c++

Question

I'm trying to add a wide character string to registry in C++. The problem is that the RegSetValueEx() function does not support wide chars, it only supports BYTE type (BYTE = unsigned char).
WCHAR myPath[] = "C:\\éâäà\\éâäà.exe"
RegSetValueExA(HKEY_CURRENT_USER, "MyProgram", 0, REG_SZ, myPath, sizeof(myPath)); // error: cannot convert argument 5 from WCHAR* to BYTE*
And please don't tell me I should convert WCHAR to BYTE because characters such as é and â can't be stored as 8 bit characters.
I'm sure this is possible because I tried opening regedit and adding a new key with value C:\\éâäà\\éâäà.exe and it worked. I wonder how other programs can add themselves to startup on a Russian or Chinese computer.
Is there another way to do so? Or is there a way to format wide character path using wildcards?
Edit: The Unicode version of the function RegSetValueExW() only changes the type of the second argument.

Answer 1

You are calling RegSetValueExA() when you should be calling RegSetValueExW() instead. But in either case, RegSetValueEx() writes bytes, not characters, that is why the lpData parameter is declared as BYTE*. Simply type-cast your character array. The REG_SZ value in the dwType parameter will let RegSetValueEx() know that the bytes represent a Unicode string. And make sure to include the null terminator in the value that you pass to the cbData parameter, per the documentation:
cbSize [in]
The size of the information pointed to by the lpData parameter, in bytes. If the data is of type REG_SZ, REG_EXPAND_SZ, or REG_MULTI_SZ, cbData must include the size of the terminating null character or characters.
For example:
WCHAR myPath[] = L"C:\\éâäà\\éâäà.exe";
RegSetValueExW(HKEY_CURRENT_USER, L"MyProgram", 0, REG_SZ, (LPBYTE)myPath, sizeof(myPath));
Or:
LPCWSTR myPath = L"C:\\éâäà\\éâäà.exe";
RegSetValueExW(HKEY_CURRENT_USER, L"MyProgram", 0, REG_SZ, (LPCBYTE)myPath, (lstrlenW(myPath) + 1) * sizeof(WCHAR));
That being said, you should not be writing values to the root of HKEY_CURRENT_USER itself. You should be writing to a subkey instead, eg:
WCHAR myPath[] = L"C:\\éâäà\\éâäà.exe";
if (RegCreateKeyEx(HKEY_CURRENT_USER, L"Software\\MyProgram", 0, NULL, REG_OPTION_NON_VOLATILE, KEY_SET_VALUE, NULL, &hKey, NULL) == 0)
{
RegSetValueExW(hKey, L"MyValue", 0, REG_SZ, (LPBYTE)myPath, sizeof(myPath));
RegCloseKey(hKey);
}

Answer 2

It seems to me you're trying to use the narrow/non-wide-char version of that function, which will only support ASCII. How about trying RegSetValueExW? Maybe you should also look up how the Windows API tries to supports ASCII and UNICODE as transparently as possible.

Answer 3

Edit: The Unicode version of the function RegSetValueExW() only changes the type of the second argument.
No it does not.
REG_SZ: A null-terminated string. This will be either a Unicode or an ANSI string, depending on whether you use the Unicode or ANSI functions.
From here:
https://learn.microsoft.com/en-us/windows/win32/sysinfo/registry-value-types