Neater way of preparing call to system()

I need to issue a CPYF using system() that would look something like this
from RPG:

cmdstring = 'CPYF FROMFILE(MYLIB/MYFILE) TOFILE+
(FTPLIB/FILEX) FROMMBR(' + %trimr(pmbr) +') +
TOMBR(' + %trimr(pmbr) + ') MBROPT(*REPLACE) FMTOPT(*NOCHK)';

That is, the command is hard coded except for the member names, which can be
anywhere between 2 and 10 bytes.
Does anyone have any good suggestions for a C/C++ equivalent? The best I can
come up with at present includes a lot of inserts and appends and would take
several lines.

Thanks,
Erik