These functions are GNU extensions, not in C or POSIX.
Clearly, the names were badly chosen.
Many systems (like MacOS) have incompatible functions called
-.IR dprintf (),
+.BR dprintf (),
usually some debugging version of
-.IR printf (),
+.BR printf (),
perhaps with a prototype like
.BI "void dprintf (int level, const char *" format ", ...);"
intended to be portable.
A better name would have been
-.IR fdprintf ().
+.BR fdprintf ().
.SH "SEE ALSO"
.BR printf (3)