How to read QWORD (64-bit) from the registry in C++?

Question

How do I read a REG_QWORD from the registry? Most specifically the HardwareInformation.qwMemorySize . I found that with it divided by 1024 then once again divided by 1024 you can get the Video memory in megabytes. How can I read the QWORD first? I can only find how to read DWORDs.

Answer 1

You read a QWORD the exact same way you read a DWORD, using RegQueryValueEx(), just with a 64-bit integer variable instead of a 32-bit integer variable, eg:

HKEY hKey;
if (RegOpenKeyEx(..., KEY_QUERY_VALUE, &hKey) == ERROR_SUCCESS) {
    QWORD value = 0; // or UINT64, ULONGLONG, ULONG64, ULARGE_INTEGER, etc...
    DWORD dwType, dwSize = sizeof(value);

    if (RegQueryValueEx(hKey, _T("HardwareInformation.qwMemorySize"), NULL, &dwType, reinterpret_cast<LPBYTE>(&value), &dwSize) == ERROR_SUCCESS) {
        if (dwType == REG_QWORD || dwType == REG_BINARY) {
            // use value as needed...
        }
    }

    RegCloseKey(hKey);
}

Or, using RegGetValue() instead:

QWORD value = 0; // see above...
DWORD dwSize = sizeof(value);

if (RegGetValue(hkey, NULL, _T("HardwareInformation.qwMemorySize"), RRF_RT_QWORD, NULL, &value, &dwSize) == ERROR_SUCCESS) {
    // use value as needed...
}