dtefldn - find effective field number of nth field in dictionary
int dtefldn (fp, n)
Dtefldn looks up the nth field in an open RMS dictionary file. If
the field is not an alias field, the function returns n. If the
field is an alias field, it returns the field number of its
effective data field, i.e. the field number that the nth field is
an alias of. The dictionary fields are numbered starting at 1.
Fp is the value returned from dtdict(C-3) or dtopen(C-3).
dtopen(C-3), dtefld(C-3), dtfindn(C-3)
Chapter 4, RMS Programming Guide
A value of -1 is returned if the field is not in the RMS
dictionary file or if fp is not an opened RMS dictionary file.