V8/usr/man/man3/dbm.3

.TH DBM 3X 
.SH NAME
dbminit, fetch, store, delete, firstkey, nextkey \- database subroutines
.SH SYNOPSIS
.nf
.PP
.B typedef struct {
.B "	char *dptr;"
.B "	int dsize;"
.B } datum;
.PP
.B dbminit(file)
.B char *file;
.PP
.B datum fetch(key)
.B datum key;
.PP
.B store(key, value)
.B datum key, value;
.PP
.B delete(key)
.B datum key;
.PP
.B datum firstkey()
.PP
.B datum nextkey(key)
.B datum key;
.SH DESCRIPTION
These functions maintain
key/value pairs in a data base.
The functions will handle very large databases
in one or two file system accesses per key.
The functions are loaded
with
.IR ld (1)
option
.BR \-ldbm .
.PP
.IR Key s
and
.IR value s
are
described by the
.I datum
typedef.
A
.I datum
specifies a string of
.I dsize
bytes pointed to by
.I dptr.
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.
.PP
Before a database can be accessed,
it must be opened by
.I dbminit.
At the time of this call,
the files
.IB file .dir
and
.IB file .pag
must exist.
(An empty database is created by
creating zero-length
`.dir' and `.pag' files.)
.PP
Once open,
the data stored under a key is
accessed by
.I fetch
and data is placed under a key
by
.IR store .
A key and its associated value
are deleted by
.IR delete .
A linear pass through all keys in a database
may be made,
in random order,
by use of
.I firstkey
and
.IR nextkey .
.I Firstkey
will return the first key
in the database.
With any key
.I nextkey
will return the next key in the database.
This code will traverse the data base:
.IP
for(key = firstkey(); key.dptr != NULL; key = nextkey(key))
.SH DIAGNOSTICS
All functions that return an
.I int
indicate errors with negative values.
A zero return indicates success.
Routines that return a
.I datum
indicate errors with a null (0)
.I dptr.
.SH SEE ALSO
cbt(3)
.SH BUGS
The
`.pag'
file will contain holes so
that its apparent size is about
four times its actual content.
These files cannot be copied
by normal means (cp, cat, tp, tar, ar)
without filling in the holes.
.br
.I Dptr
pointers returned
by these subroutines
point into static storage
that is changed by subsequent calls.
.br
The sum of the sizes of
a
key/value pair must not exceed
a fixed internal block size.
Moreover all key/value pairs that hash
together must fit on a single block.
.I Store
will return an error in the event that
a disk block fills with inseparable data.
.br
.I Delete
does not physically reclaim file space,
although it does make it available for reuse.