dnumidx - set significant fields for index query
#include
int dnumidx (n, fcb)
int n;
DFILE *fcb;
An RMSfile may have one primary and several secondary keys
defined for rapid searching of the RMSfile records. Each key can
be composed of one to eight fields concatenated together. When
values are supplied for each field of a key, the associated
record, if any, can be found quickly using an index.
When only some of the fields in a key are known, the index
searches can still be used. However, an exact match is not
guaranteed in this case. There may be several records that match
the partial key value. The important thing to remember is that
only the beginning fields of an index may be used. You cannot,
for example, search an index using the last of four fields in a
key.
To accurately search an index using a partial key, three things
must be done: select a key, specify the number of fields being
used in that key, and read the records in index order. Call
dseti(C-3) to specify the desired key.
Call dnumidx to specify
the desired number of fields. Finally, call one of the index find
functions dfindi(C-3), dfindni(C-3),
dfindpi(C-3), dfindm(C-3),
dfindnm(C-3), dfindpm(C-3),
or dfindlm(C-3) to return records
from the RMSfile in index order starting at the given key value.
The data buffer values must be checked after record is read to
determine when enough data has been read (for 8-100 C/Base
Functions example, dfindi only guarantees values equal to or
greater than the key values specified).
n is the number of fields in the key that are significant. As
stated before, this number means that the first n field(s) are
significant.
Fcb is the file block pointer returned by dopen(C-3)
or
dlopen(C-3).
dlopen(C-3), dopen(C-3),
dseti(C-3) dfindi(C-3),
dfindni(C-3),
dfindpi(C-3), dfindm(C-3),
dfindnm(C-3), dfindpm(C-3),
dfindlm(C-3)
Dnumidx returns a value of -1 (BAD) if fcb is not a valid open
file block pointer, if there is no current index, or if the
number of fields parameter, n, is less than zero or greater than
the number of fields in the index.