Reference

dbm(3)

database access functions

NAME

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

SYNOPSIS

#include <ndbm.h>

int

dbm_clearerr(DBM *db);

void

dbm_close(DBM *db);

int

dbm_delete(DBM *db, datum key);

int

dbm_dirfno(DBM *db);

int

dbm_error(DBM *db);

datum

dbm_fetch(DBM *db, datum key);

datum

dbm_firstkey(DBM *db);

datum

dbm_nextkey(DBM *db);

DBM *

dbm_open(const char *file, int open_flags, mode_t file_mode);

int

dbm_store(DBM *db, datum key, datum content, int store_mode);

DESCRIPTION

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

datum is declared in ⟨ndbm.h⟩:

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

The dbm_open(file, open_flags, file_mode) function opens or creates a database file. The file argument is the basename of the file containing the database; the actual database has a .db suffix. I.e., if file is "/home/me/mystuff" then the actual database is in the file /home/me/mystuff.db. The open_flags and file_mode arguments are passed to open(2). (O_RDWR | O_CREAT) is a typical value for open_flags; 0660 is a typical value for file_mode. O_WRONLY is not allowed in open_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, content, store_mode) function inserts or replaces an entry in the database. The store_mode argument is either DBM_INSERT or DBM_REPLACE. If store_mode 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 store_mode 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 content corresponding to key.

The dbm_delete(db, key) function deletes the entry for key. The dbm_delete() function normally returns zero but returns 1 if there was no entry with key in the database 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.

LEGACY SYNOPSIS

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

The include file ⟨ndbm.h⟩ is necessary for all functions.

DBM *
dbm_open(const char *file, int open_flags, int file_mode);

file_mode has type int.

SEE ALSO

open(2), dbopen(3), hash(3), compat(5)

STANDARDS

These functions (except dbm_dirfno()) are included in the Version 2 of the Single UNIX Specification (“SUSv2”).

History