dbminit, fetch, store, delete, firstkey, nextkey \- data base subroutines
.B "typedef struct { char *dptr; int dsize; } datum;"
key/content pairs in a data base.
The functions will handle very large
databases and will access a keyed item
in one or two filesystem accesses.
The functions are obtained with the loader option
Arbitrary binary data, as well as normal
ASCII strings, are allowed.
The data base is stored in two files.
One file is a directory containing a bit map
and has `.dir' as its suffix.
The second file contains all data and
has `.pag' as its suffix.
Before a database can be accessed,
At the time of this call,
(An empty database is created by
`.dir' and `.pag' files.)
the data stored under a key is
and data is placed under a key
A key (and its associated contents)
A linear pass through all keys in a database
in an (apparently) random order,
will return the first key
will return the next key in the database.
This code will traverse the data base:
for(key=firstkey(); key.dptr!=NULL; key=nextkey(key))
All functions that return an
indicate errors with negative values.
A zero return indicates ok.
indicate errors with a null (0)
file will contain holes so
that its apparent size is about
four times its actual content.
Older UNIX systems may create real
file blocks for these holes when touched.
These files cannot be copied
by normal means (cp, cat, tp, tar, ar)
without filling in the holes.
point into static storage
that is changed by subsequent calls.
key/content pair must not exceed
Moreover all key/content pairs that hash
together must fit on a single block.
will return an error in the event that
a disk block fills with inseparable data.
does not physically reclaim file space,
although it does make it available for reuse.
The order of keys presented by
depends on a hashing function, not on anything