C++ - getting null values in value read from registry

Question

My application properly reads and writes to the registry. Now, I need to read a registry value from:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Cryptography\MachineGuid

Here is my code:

bool GetWindowsID(string &winID)
{
    HKEY hKey = 0, hKeyType = HKEY_LOCAL_MACHINE;
    bool status = false;
    DWORD dwType = 0;
    DWORD dwBufSize = 256;
    char value[256] = "\0";
    if (RegOpenKeyEx(hKeyType, L"SOFTWARE\\Microsoft\\Cryptography", NULL, KEY_QUERY_VALUE|KEY_WOW64_64KEY, &hKey) == ERROR_SUCCESS)
    {
        dwType = REG_SZ;
        if (RegQueryValueEx(hKey, L"MachineGuid", NULL, &dwType, (LPBYTE)value, &dwBufSize) == ERROR_SUCCESS)
            status = true;
        RegCloseKey(hKey);
    }
    winID.assign(value);
    return status;
}

I get the guid but in value array after each character their is a "\\0" value due to which only first character of array gets assigned to string. This is wierd!

Answer 1

You have built targeting Unicode and so the registry API is returning UTF-16 Unicode text. Instead of char use wchar_t and remember that each wchar_t element is 2 bytes wide.

Do also make sure that you account for the returned string not being null-terminated, as described in the documentation. You must take account of the value returned in dwBufSize .

Answer 2

I get the guid but in value array after each character their is a "\\0" value due to which only first character of array gets assigned to string. This is wierd!

This is because you are calling the Unicode version of RegQueryValueEx() , so the string is returned in Unicode (UTF-16).

You will have to use wide character parameters to get the value.

Change this line:

char value[256] = "\0";

To use wchar_t instead.