How to correctly pass in RegSetValueEx to lpData NULL?

Question

C++ / C#

The crux of the matter is what. I wrote a function like this:

bool modifyKey(HKEY _hKey, wstring path, LPCWSTR name, LPCWSTR value) {
  HKEY hKey;
  if (RegOpenKey(_hKey, path.data(), &hKey) == ERROR_SUCCESS) {
    if (RegSetValueEx(hKey, name, NULL, REG_SZ, (BYTE*)value, sizeof(value)) == ERROR_SUCCESS) {//SIZEOF(VALUE), сюда не смотреть, я уже пробовал по разному и оставил так.
        return RegCloseKey(hKey) == ERROR_SUCCESS;
    }
    else {
      RegCloseKey(hKey);
    }
  }
  else {
    if (RegCreateKey(_hKey, path.data(), &hKey) == ERROR_SUCCESS) {
      if (RegSetValueEx(hKey, name, NULL, REG_SZ, (BYTE*)value, sizeof(value)) == ERROR_SUCCESS)//SIZEOF(VALUE), сюда не смотреть, я уже пробовал по разному и оставил так. {
        return RegCloseKey(hKey) == ERROR_SUCCESS;
      }
      else {
        RegCloseKey(hKey);
      }
    }
  }
  return false;
}

I need to create an empty data skeleton in the registry in a certain path.
And so it turns out that NULL gets into the variables name, value from time to time.
The problem itself is that the program crashes because I want to get the length of the string (wcslen) or its dimensions (sizeof). the variable value is NULL.
How to fix this and it would be interesting to know what needs to be passed to the RegSetValueEx function in cbData ?

Answer 1

Let's start simple.
sizeof( expresion )allows you to find out the minimum allowed amount of memory required in order for the memory to hold an object with an assertion result type of expresion.
sizeof( value )will return the size LPCWSTR, i.e. type size const wchar_t*.
wcslen does not allow zero to be passed as its parameter. It is entirely up to you to take care of this.
RegSetValueExW can take zero in the parameter lpData, but then it cbDatamust contain 0. But in general, this is a very bad practice. If you need to write an empty string, write an empty one. line. Those. "", but not zero.
cbDatamust be given by the size of the string buffer in bytes, including the terminal character, or both terminal characters in the case of a multiline argument in lpData. An important note is that the cbDatasize is indicated in bytes, not in characters. You are lpDatapassing a string from wchar_t, the size of which is more than one byte.
Further, according to the code itself. Its hard to read.

How to read easier

bool modifyKey( HKEY root_hey, const std::wstring_view& path, const std::wstring_view& key_name, const std::wstring_view& new_value )
{
   HKEY folder_key;

   if( RegCreateKeyW( root_hey, path.data(), &folder_key ) != ERROR_SUCCESS )
   {
      return false;
   }

   const BYTE* const value_buffer = reinterpret_cast<const BYTE*>( new_value.data() );
   const DWORD buffer_size = static_cast<DWORD>( new_value.length() * sizeof( wchar_t ) + 1 );
   if( RegSetValueExW( folder_key, key_name.data(), 0, REG_SZ, value_buffer, buffer_size ) != ERROR_SUCCESS )
   {
      RegCloseKey( folder_key );
      return false;
   }

   if( RegFlushKey( folder_key ) != ERROR_SUCCESS )
   {
      RegCloseKey( folder_key );
      return false;
   }

   RegCloseKey( folder_key );
   return true;
}