dbm man page on Xenix

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     DBM(S)		      XENIX System V			DBM(S)

     Name
	  dbminit, fetch, store, delete, firstkey, nextkey - Performs
	  database functions.

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

	  int dbminit(file)
	  char *file;

	  datum fetch(key)
	  datum key;

	  int store(key, content)
	  datum key, content;

	  int delete(key)
	  datum key;

	  datum firstkey();

	  datum nextkey(key);
	  datum key;

     Description
	  These functions maintain key/content pairs in a database.
	  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 database 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 database:

     Page 1					      (printed 8/7/87)

     DBM(S)		      XENIX System V			DBM(S)

	       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.

     Notes
	  The .pag file will contain holes so that its apparent size
	  is about four times its actual content.  Older XENIX 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.

	  These routines are not reentrant, so they should not be used
	  on more than one database at a time.

     Credit
	  This utility was developed at the University of California
	  at
	  Berkeley and is used with permission.

     Page 2					      (printed 8/7/87)

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