These functions are GNU extensions, not in C or POSIX. Clearly, the names were badly chosen. Many systems (like MacOS) have incompatible functions called dprintf, usually some debugging version of printf, perhaps with a prototype like
"void dprintf (int level, const char *"format", ...);"
where the first parameter is a debugging level (and output is to stderr). Moreover, dprintf (or DPRINTF) is also a popular macro name for a debugging printf. So, probably, it is better to avoid this function in programs intended to be portable.
A better name would have been fdprintf.