in C++ files: what a file opened as an ios::binary differs from one opened as ios::binary | ios::out?

Question

if i opened a file like:

ofstream file("file.dat",ios::binary);

or

ofstream file("file.dat",ios::binary | ios::out);

what can i do with a file opened in the latter form that i can't do with the former form and vice versa

thank you

Answer 1

For an ofstream, ios::out is the default, so there's no difference. I believe the only time specifying ios::out makes a difference is if you use an fstream, which can be opened for reading or writing, or both.

Answer 2

In most cases I would expect there to be no difference, though it seems like this could technically be implementation specific.

In my implementation (gcc 3.4.3) the open for the ofstream uses the ios:::out mode in the ofstream->open() call regardless of what is specified via the constructor so it's purely optional. If using fstream, this is not the case and would need to be specified explicitly.