flags of open operation c++
in input File open for reading: the internal stream buffer supports input operations.
out output File open for writing: the internal stream buffer supports output operations.
binary binary Operations are performed in binary mode rather than text.
ate at end The output position starts at the end of the file.
app append All output operations happen at the end of the file, appending to its existing contents.
trunc truncate Any contents that existed in the file before it is open are discarded.