DBM(3X) 																   DBM(3X)

NAME

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

SYNOPSIS

       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

       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 filesystem 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.

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 512 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.

																	   DBM(3X)