There are two types of stream orientation for input and output, a wide-character (wchar_t) oriented and a byte (char) oriented. A stream is un-oriented after that stream is associated with a file, until a byte or wide-character input/output operation occurs.

Once any input/output operation is performed on that stream, that stream becomes oriented by that operation to be either byte oriented or wide-character oriented and remains that way until the file has been closed and reopened.

After a stream orientation is established, any call to an input/output function of the other orientation is not applied. For example, a byte-oriented input/output function does not have an effect on a wide-oriented stream.