sputbackc
if (good() && _strbuf->sputbackc(ch) == EOF) clear(ios::badbit);
int sputbackc(char c);
return get_stream()->sputbackc(c);
sb->sputbackc(ch);
sb->sputbackc(ch);
sb->sputbackc(ch);
ins._strbuf->sputbackc(ch);
_strbuf->sputbackc(ch);