Write PUNICODE_STRING to file, got garbage data - c++

Question

I'm trying to write two PUNICODE_STRING structure to file, but the data written is invalid, any ideas?
(The data1 is 123 and data2 is 456 in this case)
DWORD dwBytesWritten = 0;
WCHAR buffer[1024];
HANDLE hFile = CreateFile(L"c:\\log.txt", FILE_APPEND_DATA, 0, NULL,
OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile != INVALID_HANDLE_VALUE)
{
memset(buffer, 0, sizeof(buffer));
wsprintf(buffer, L"%s :: %s\r\n", Data1->Buffer, Data2->Buffer);
WriteFile(hFile, buffer, wcslen(buffer), &dwBytesWritten, NULL);
CloseHandle(hFile);
}

Answer 1

main error is
WriteFile(hFile, buffer, wcslen(buffer), &dwBytesWritten, NULL);
WriteFile always take The number of bytes to be written to the file. but wcslen return the number of characters which in case UINICODE in 2 time less - need * sizeof(WCHAR) or << 1
then for format UNICODE_STRING need use %wZ format - because in general case Buffer can be not 0 terminated. and better use swprintf or _snwprintf instead wsprintf.
at the last always better dynamic allocate needed buffer, then use hardcoded size, which can be overwritten
so i be use next code:
void test(PCUNICODE_STRING Data1, PCUNICODE_STRING Data2)
{
DWORD dwBytesWritten;
PWSTR buffer = (PWSTR)alloca(Data1->Length + Data2->Length + sizeof(L" :: \r\n"));
int n = swprintf(buffer, L"%wZ :: %wZ\r\n", Data1, Data2) * sizeof(WCHAR);
HANDLE hFile = CreateFile(L"c:\\log.txt", FILE_APPEND_DATA, 0, NULL,
OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile != INVALID_HANDLE_VALUE)
{
WriteFile(hFile, buffer, n, &dwBytesWritten, NULL);
CloseHandle(hFile);
}
}