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Defined in rt_sys.h, the _sys_write() function writes the contents of a buffer to a file previously opened with _sys_open().


int _sys_write(FILEHANDLE fh, const unsigned char *buf, unsigned len, int mode);


The mode parameter is here for historical reasons. It contains nothing useful and must be ignored.


The return value is either:

  • A positive number representing the number of characters not written (so any nonzero return value denotes a failure of some sort).

  • A negative number indicating an error.