dbminit man page on Ultrix

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dbm(3x)								       dbm(3x)

Name
       dbminit,	 fetch,	 store,	 delete, firstkey, nextkey - data base subrou‐
       tines

Syntax
       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	 func‐
       tions  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 speci‐
       fies 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 At the time  of
       this call, the files file.dir and file.pag must exist.  (An empty data‐
       base is created by creating zero-length `.dir' and `.pag' files.)

       Once open, the data stored under a key  is  accessed  by	 and  data  is
       placed under a key by A key (and its associated contents) is deleted by
       A linear pass through all keys in a database may be made, in an (appar‐
       ently) random order, by use of and The will return the first key in the
       database.  With any 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))

Restrictions
       The  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 without filling in the holes.

       The dptr pointers returned by these subroutines point into static stor‐
       age 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.  The will return an error  in
       the event that a disk block fills with inseparable data.

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

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

								       dbm(3x)
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