30 Input/output library [input.output]

30.5 Iostreams base classes [iostreams.base]

30.5.3 Class ios_­base [ios.base]

30.5.3.1 Types [ios.types]

30.5.3.1.4 Type ios_­base​::​openmode [ios::openmode]

using openmode = T3;
The type openmode is a bitmask type.
It contains the elements indicated in Table 102.
Table 102openmode effects
Element
Effect(s) if set
app
seek to end before each write
ate
open and seek to end immediately after opening
binary
perform input and output in binary mode (as opposed to text mode)
in
open for input
out
open for output
trunc
truncate an existing stream when opening