bool wstring2string(IN const wchar_t* lpwstr, OUT string& str, IN unsigned int uCodePage)
{
	if (NULL == lpwstr)
		return false;

	int nLen = ::WideCharToMultiByte(uCodePage, 0, lpwstr, -1, NULL, 0, NULL, NULL);
	char* pBuf = new char[nLen + 1];
	if (NULL != pBuf)
	{
		nLen = ::WideCharToMultiByte(uCodePage, 0, lpwstr, -1, pBuf, nLen, NULL, NULL);
		pBuf[nLen] = '\0';
		str	= pBuf;
		delete pBuf;		
		return true;
	}

	return false;
}

bool UnicodeToUTF8(IN const wchar_t* lpwstr, OUT string& str)
{
	return wstring2string(lpwstr, str, CP_UTF8);
}

void ConvertCString2string(CString& strSrc,std::string& strDes) 
{ 
#ifndef UNICODE 
	strDes = strSrc; 
#else 
	USES_CONVERSION; 
	strDes = W2A(strSrc.LockBuffer()); 
	strSrc.UnlockBuffer(); 
#endif 
}

std::string ws2s(const std::wstring& ws)
{
    std::string curLocale = setlocale(LC_ALL, NULL);        // curLocale = "C";
    setlocale(LC_ALL, "chs");
    const wchar_t* _Source = ws.c_str();
    size_t _Dsize = 2 * ws.size() + 1;
    char *_Dest = new char[_Dsize];
    memset(_Dest,0,_Dsize);
    wcstombs(_Dest,_Source,_Dsize);
    std::string result = _Dest;
    delete []_Dest;
    setlocale(LC_ALL, curLocale.c_str());
    return result;
}

std::wstring s2ws(const std::string& s)
{
    setlocale(LC_ALL, "chs"); 
    const char* _Source = s.c_str();
    size_t _Dsize = s.size() + 1;
    wchar_t *_Dest = new wchar_t[_Dsize];
    wmemset(_Dest, 0, _Dsize);
    mbstowcs(_Dest,_Source,_Dsize);
    std::wstring result = _Dest;
    delete []_Dest;
    setlocale(LC_ALL, "C");
    return result;
}

Call c_str() to get a const char * (LPCSTR) from a std::string.
It's all in the name:
LPSTR - (long) pointer to string - char *
LPCSTR - (long) pointer to constant string - const char *
LPWSTR - (long) pointer to Unicode (wide) string - wchar_t *
LPCWSTR - (long) pointer to constant Unicode (wide) string - const wchar_t *
LPTSTR - (long) pointer to TCHAR (Unicode if UNICODE is defined, ANSI if not) string - TCHAR *
LPCTSTR - (long) pointer to constant TCHAR string - const TCHAR *
You can ignore the L (long) part of the names -- it's a holdover from 16-bit Windows.