cpp/io/vprint unicode

Format according to the format string, and writes the result to the stream.

Let be a temporary std produced by formatting the arguments in  with.

@1@ If refers to a terminal capable of displaying Unicode, writes  to this terminal using the native Unicode API. Otherwise, writes unmodified to the.

@2@ same as when  is equal to the standard C output stream stdout, i.e.

The behavior is undefined if:
 * is not a valid pointer to a C stream;
 * contains invalid Unicode code units.

Return value
(none)