int ctl_stream_printf(CTL_STREAM_t s, const char *fmt, ...);
ctl_stream_printf writes to the stream s under control of the string pointed to by fmt that specifies how subsequent arguments are converted for output.
If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated but are otherwise ignored.
ctl_stream_printf returns the number of characters transmitted, or a negative value if an output or encoding error occurred.