conversion of Cstring to BYTE

Question

I am using Visual Studio c++ and want to convert the Cstring to Byte. I have written this code but it gave me error in the second line that "data" is undefined.

CString data = _T( "OK");
LPBYTE pByte = new BYTE[data.GetLength() + 1];
memcpy(pByte, (VOID*)LPCTSTR(data), data.GetLength());

Further more I need to convert LPBYTE to const char for strcmp function. I have written the code but I can't find the issue with it.

const LPBYTE lpBuffer;
LPBYTE lpData = lpBuffer;
CString rcvValue(LPCSTR(lpBuffer));
const CHAR* cstr = (LPCSTR)rcvValue;
if (strcmp (cstr,("ABC")) == 0)
{
    ////
}

Answer 1

The CString type is a template specialization of CStringT, depending on the character set it uses (CStringA for ANSI, CStringW for Unicode). While you ensure to use a matching encoding when constructing from a string literal by using the _T macro, you fail to account for the different size requirements when copying the controlled sequence to the buffer.

The following code fixes the first part:

CString data = _T("OK");
size_t size_in_bytes = (data.GetLength() + 1) * sizeof(data::XCHAR);
std::vector<BYTE> buffer(size_in_bytes);
unsigned char const* first = static_cast<unsigned char*>(data.GetString());
unsigned char const* last = first + size_in_bytes;
std::copy(first, last, buffer.begin());

The second question is really asking to solve a solved problem. The CStringT type already provides a CStringT::Compare member, that can be used:

const LPBYTE lpBuffer;
CString rcvValue(static_cast<char const*>(lpBuffer));
if (rcvValue.Compare(_T("ABC")) == 0)
{
    ////
}

General advice: Always prefer using the concrete CStringT specialization matching your character encoding, i.e. CStringA or CStringW. The code will be much easier to read and reason about, and when you run into problems you need help with, you can post a question at Stack Overflow, without having to explain, what compiler settings you are using.