DBM(3X) 																   DBM(3X)

NAME

       dbminit, fetch, store, delete, firstkey, nextkey - data base subroutines

SYNOPSIS

       #include <dbm.h>

       typedef struct {
	    char *dptr;
	    int dsize;
       } datum;

       dbminit(file)
       char *file;

       datum fetch(key)
       datum key;

       store(key, content)
       datum key, content;

       delete(key)
       datum key;

       datum firstkey()

       datum nextkey(key)
       datum key;

DESCRIPTION

       Note:  the  dbm library has been superceded by ndbm(3), and is now implemented using ndbm.  These functions maintain key/content pairs in a
       data base.  The functions will handle very large (a billion blocks) databases and will access a keyed  item  in	one  or  two  file  system
       accesses.  The functions are obtained with the loader option -ldbm.

       Keys  and  contents  are  described  by the datum typedef.  A datum specifies a string of dsize bytes pointed to by 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.

       Before  a  database  can  be accessed, it must be opened by dbminit.  At the time of this call, the files file.dir and file.pag must exist.
       (An empty database is created by creating zero-length `.dir' and `.pag' files.)

       Once open, the data stored under a key is accessed by fetch and data is placed under a key by store.  A key (and its  associated  contents)
       is  deleted  by	delete.  A linear pass through all keys in a database may be made, in an (apparently) random order, by use of firstkey and
       nextkey.  Firstkey will return the first key in the database.  With any key nextkey will return the next key in the  database.	This  code
       will traverse the data base:

	      for (key = firstkey(); key.dptr != NULL; key = nextkey(key))

DIAGNOSTICS

       All  functions that return an int indicate errors with negative values.	A zero return indicates ok.  Routines that return a datum indicate
       errors with a null(0) dptr.

SEE ALSO

       ndbm(3)

BUGS

       The `.pag' 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.

       Dptr pointers returned by these subroutines point into static storage that is changed by subsequent calls.

       The sum of the sizes of a key/content pair must not exceed the internal block size (currently 1024 bytes).  Moreover all key/content  pairs
       that hash together must fit on a single block.  Store will return an error in the event that a disk block fills with inseparable data.

       Delete does not physically reclaim file space, although it does make it available for reuse.

       The order of keys presented by firstkey and nextkey depends on a hashing function, not on anything interesting.

4th Berkeley Distribution					   May 12, 1986 							   DBM(3X)