How to determine the character encoding that a terminal uses in a C/C++ program?

I’ve noticed that SyncTERM uses a different character encoding than the default MacOS terminal emulator, and they’re incompatible with one another. For example, say you want to print a block character in a format string. In SyncTERM, which uses the IBM Extended ASCII character encoding, you would use an octal escape sequence like 261. In (and probably iTerm2 as well), this just prints a question mark. Since these terminals use UTF-8, you need to use the uxxxx escape sequence.

How are long command lines ( > $COLUMNS ) automatically wrapped to a new line?

There are several points where I/O is passed through, some of which (to my knowledge) are the shell, pty, tty, termios, terminal emulator application. In most terminal emulators, long command lines (ones that exceed current $COLUMNS) are wrapped to a new line before the user submits the command by pressing Enter. Also, the line is wrapped backward to the line above when the appropriate number of characters are removed from the command line as one would expect.