h = CreateFileW(L"d:\\1.txt", FILE_WRITE_DATA, FILE_SHARE_READ, nullptr, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr);
char buf[] = "DB ";
WriteFile(h, buf, sizeof(buf) - 1, nullptr, nullptr);

for (int i = 0; i < 5; ++i)
{
   buf[0] = (char)('1' + i);
   buf[1] = ',';
   WriteFile(h, buf, 2, nullptr, nullptr);
}

SetFilePointer(h, -1, nullptr, FILE_CURRENT);
buf[0] = ' ';
WriteFile(h, buf, 1, nullptr, nullptr);//clear last ',' in file
CloseHandle(h);