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Manual Pages  — DBM


dbm_clearerr, dbm_close, dbm_delete, dbm_dirfno, dbm_error, dbm_fetch, dbm_firstkey, dbm_nextkey, dbm_open, dbm_store – database access functions



#include <fcntl.h>
#include <ndbm.h>

dbm_open(const char *base, int flags, mode_t mode);

dbm_close(DBM *db);

dbm_store(DBM *db, datum key, datum data, int flags);

dbm_fetch(DBM *db, datum key);

dbm_delete(DBM *db, datum key);

dbm_firstkey(DBM *db);

dbm_nextkey(DBM *db);

dbm_error(DBM *db);

dbm_clearerr(DBM *db);

dbm_dirfno(DBM *db);


Database access functions. These functions are implemented using dbopen(3) with a hash(3) database.

datum is declared in <ndbm.h>:

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

The dbm_open(base, flags, mode) function opens or creates a database. The base argument is the basename of the file containing the database; the actual database has a .db suffix. I.e., if base is "/home/me/mystuff" then the actual database is in the file /home/me/mystuff.db. The flags and mode arguments are passed to open(2). ( O_RDWR | O_CREAT) is a typical value for flags; 0660 is a typical value for mode. O_WRONLY is not allowed in flags. The pointer returned by dbm_open() identifies the database and is the db argument to the other functions. The dbm_open() function returns NULL and sets errno if there were any errors.

The dbm_close(db) function closes the database.

The dbm_store(db, key, data, flags) function inserts or replaces an entry in the database. The flags argument is either DBM_INSERT or DBM_REPLACE. If flags is DBM_INSERT and the database already contains an entry for key, that entry is not replaced. Otherwise the entry is replaced or inserted. The dbm_store() function normally returns zero but returns 1 if the entry could not be inserted (because flags is DBM_INSERT, and an entry with key already exists) or returns -1 and sets errno if there were any errors.

The dbm_fetch(db, key) function returns NULL or the data corresponding to key.

The dbm_delete(db, key) function deletes the entry for key. The dbm_delete() function normally returns zero or returns -1 and sets errno if there were any errors.

The dbm_firstkey(db) function returns the first key in the database. The dbm_nextkey(db) function returns subsequent keys. The db_firstkey() function must be called before dbm_nextkey(). The order in which keys are returned is unspecified and may appear random. The dbm_nextkey() function returns NULL after all keys have been returned.

The dbm_error(db) function returns the errno value of the most recent error. The dbm_clearerr(db) function resets this value to 0 and returns 0.

The dbm_dirfno(db) function returns the file descriptor to the database.


open(2), dbopen(3), hash(3)


These functions (except dbm_dirfno()) are included in the Version 2 of the Single UNIX Specification.


The functions dbminit(), fetch(), store(), delete(), firstkey(), and nextkey() first appeared in AT&T v7 .

DBM (3) April 2, 2022

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