const LPCWSTR testfile = L"testfile.txt";

    LPCWSTR test1 = L"test simple text"; // Длина 16, вес  = 32
    SIZE_T size = _tcsclen(test1);
    //size++;
    SIZE_T size_in_bytes = sizeof(WCHAR)*size;
    std::cout << " String size: " << size << "\n";
    std::cout << " String size in bytes: " << size_in_bytes << "\n\n";

    HANDLE hFile = CreateFile(testfile, GENERIC_READ | GENERIC_WRITE, NULL, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

    SIZE_T size1 = GetFileSize(hFile, NULL); 
    std::cout << " File size: " << size1 << "\n\n ";

    HANDLE hFileMapping = CreateFileMapping(hFile, NULL, PAGE_READWRITE, NULL, size1 + size_in_bytes, NULL);

    LPCWSTR pvFile = (LPCWSTR)MapViewOfFile(hFileMapping, FILE_MAP_WRITE, NULL, NULL, NULL);

    CopyMemory((LPVOID)(pvFile + size1), test1, size_in_bytes);

    // очищаем все перед завершением
    UnmapViewOfFile(pvFile);
    CloseHandle(hFileMapping);
    CloseHandle(hFile);