dbm(3C)                                                             dbm(3C)

NAME
     dbm: dbminit, dbmclose, fetch, store, delete, firstkey, nextkey - data
     base subroutines

SYNOPSIS
     /usr/ucb/cc [flag ...] file ... -ldbm

     #include <dbm.h>

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

     int dbminit(char *file);

     int dbmclose(void);

     datum fetch(datum key);

     int store(datum key, datum content);

     int delete(datum key);

     datum firstkey(void);

     datum nextkey(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 -l dbm.

     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 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.

     A database may be closed by calling dbmclose. You must close a data-
     base before opening a new one.

     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.



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dbm(3C)                                                             dbm(3C)

     firstkey will return the first key in the database. With any key next-
     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))

RETURN VALUE
     All functions that return an int indicate errors with negative values.
     A zero return indicates no error. Routines that return a datum indi-
     cate 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.

     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 inter-
     nal 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.

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

     Updating and reading a database concurrently can result in incon-
     sistencies.

     The same functionality can be found in the libnsl library.

SEE ALSO
     ar(1), cat(1), cp(1), tar(1), ndbm(3C).





















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