On http://www.csounds.com/manual/html/opcode.html strings are not  
mentioned as outputtypes for user defined opcodes. But something like

opcode yes, S, S
Spath xin
ipos	 strrindex	Spath,"."
istrlen	strlen	 Spath
Sname	 strsub	 Spath, 0, ipos; returns the path without the suffix
xout Sname
endop

works. But it seems to be restricted to one string; this gives an error:

opcode no, SS, S
Spath xin
ipos	 strrindex	Spath,"."
istrlen	strlen	 Spath
Sname	 strsub	 Spath, 0, ipos; returns the path without the suffix
Ssuf	 strsub	 Spath, ipos, istrlen; returns the suffix
xout Sname, Ssuf
endop

Is it possible to allow more than one string as UDO outtype?

	joachim