14.4.1.1 Open Mode

The mode is constructed by or-ing bits from the enumerated type open_mode, which is a public type of class ios and has the definition:

enum open_mode {binary=0, in=1, out=2, ate=4, app=8, trunc=0x10,
     nocreate=0x20, noreplace=0x40};

The binary flag is not needed on UNIX, but is provided for compatibility with systems that do need it. Portable code should use the binary flag when opening binary files.

You can open a file for both input and output. For example, the following code opens file someName for both input and output, attaching it to the fstream variable inoutFile.

fstream inoutFile("someName", ios::in|ios::out);