Difference between unsigned char and char pointers

Question

I'm a bit confused with differences between unsigned char (which is also BYTE in WinAPI) and char pointers.

Currently I'm working with some ATL-based legacy code and I see a lot of expressions like the following:

CAtlArray<BYTE> rawContent;
CALL_THE_FUNCTION_WHICH_FILLS_RAW_CONTENT(rawContent);
return ArrayToUnicodeString(rawContent);
// or return ArrayToAnsiString(rawContent);

Now, the implementations of ArrayToXXString look the following way:

CStringA ArrayToAnsiString(const CAtlArray<BYTE>& array)
{
    CAtlArray<BYTE> copiedArray;
    copiedArray.Copy(array);
    copiedArray.Add('\0');

    // Casting from BYTE* -> LPCSTR (const char*).
    return CStringA((LPCSTR)copiedArray.GetData());
}

CStringW ArrayToUnicodeString(const CAtlArray<BYTE>& array)
{
    CAtlArray<BYTE> copiedArray;
    copiedArray.Copy(array);

    copiedArray.Add('\0');
    copiedArray.Add('\0');

    // Same here.        
    return CStringW((LPCWSTR)copiedArray.GetData());
}

---

So, the questions:

• Is the C-style cast from BYTE* to LPCSTR (const char*) safe for all possible cases?

• Is it really necessary to add double null-termination when converting array data to wide-character string?

• The conversion routine CStringW((LPCWSTR)copiedArray.GetData()) seems invalid to me, is that true?

• Any way to make all this code easier to understand and to maintain?

Answer 1

The C standard is kind of weird when it comes to the definition of a byte. You do have a couple of guarantees though.

• A byte will always be one char in size
  • sizeof(char) always returns 1
• A byte will be at least 8 bits in size

This definition doesn't mesh well with older platforms where a byte was 6 or 7 bits long, but it does mean BYTE*, and char * are guaranteed to be equivalent.

Multiple nulls are needed at the end of a Unicode string because there are valid Unicode characters that start with a zero (null) byte.

As for making the code easier to read, that is completely a matter of style. This code appears to be written in a style used by a lot of old C Windows code, which has definitely fallen out of favor. There are probably a ton of ways to make it clearer for you, but how to make it clearer has no clear answer.