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Target-dependent I/O support functions in the C library

rt_sys.h defines the type FILEHANDLE. The value of FILEHANDLE is returned by _sys_open() and identifies an open file on the host system.

Target-dependent I/O functions use semihosting. If any function is redefined, all stream-support functions must be redefined.

If the _sys_* functions are redefined, both normal character I/O and wide character I/O works. That is, you are not required to do anything extra with these functions for wide character I/O to work.