MirBSD manpage: dbm(3), dbmclose(3), dbminit(3), delete(3), fetch(3), firstkey(3), nextkey(3), store(3)

DBM(3)                     BSD Programmer's Manual                      DBM(3)


     dbminit, dbmclose, fetch, store, delete, firstkey, nextkey - database


     #include <dbm.h>

     dbminit(const char *file);


     fetch(datum key);

     store(datum key, datum content);

     delete(datum key);


     nextkey(datum key);


     These functions provide a dbm-compatible interface to the database access
     methods described in db(3). Each unique record in the database is a
     key/content pair, the components of which may be any arbitrary binary
     data. The key and the content data are described by the datum data struc-

           typedef struct {
                   void *dptr;
                   size_t dsize;
           } datum;

     The dbminit() function is used to open a database. Before the call to
     dbminit(), the files file.pag and file.dir must exist. The user is
     responsible for creating the zero-length .pag and .dir files.

     Once the database is open, fetch() is used to retrieve the data content
     associated with the specified key. Similarly, store() is used to store
     the content data with the specified key.

     The delete() function removes the specified key and its associated con-
     tent from the database.

     The functions firstkey() and nextkey() are used to iterate over all of
     the records in the database. Each record will be reached exactly once,
     but in no particular order. The firstkey() function returns the first
     record of the database, and thereafter nextkey() returns the following
     records. The following code traverses the entire database:

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

     The behaviour of nextkey() is undefined if the database is modified after
     a call to firstkey().

     The database is closed with the dbmclose() function (it must be closed
     before a new one can be opened).

Implementation notes

     The underlying database is a hash(3) database with a bucket size of 4096,
     a filling factor of 40, default hashing function and cache size, and uses
     the host's native byte order.


     Upon successful completion, all functions that return int return a value
     of 0, otherwise a negative value is returned.

     Functions that return a datum indicate errors by setting the dptr field
     to NULL.


     db(3), hash(3), ndbm(3)


     Because the dbm routines are implemented on top of db(3), only a single
     file, file.pag, is used to actually store the database. The references to
     file.dir are purely for backwards compatibility with historic implementa-

MirBSD #10-current            February 14, 1999                              1

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