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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 

.TH "DBM_CLEARERR" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"

.\" dbm_clearerr 

.SH NAME

dbm_clearerr, dbm_close, dbm_delete, dbm_error, dbm_fetch, dbm_firstkey,

dbm_nextkey, dbm_open, dbm_store \- database

functions

.SH SYNOPSIS

.LP

\fB#include <ndbm.h>

.br

.sp

int dbm_clearerr(DBM *\fP\fIdb\fP\fB);

.br

void dbm_close(DBM *\fP\fIdb\fP\fB);

.br

int dbm_delete(DBM *\fP\fIdb\fP\fB, datum\fP \fIkey\fP\fB);

.br

int dbm_error(DBM *\fP\fIdb\fP\fB);

.br

datum dbm_fetch(DBM *\fP\fIdb\fP\fB, datum\fP \fIkey\fP\fB);

.br

datum dbm_firstkey(DBM *\fP\fIdb\fP\fB);

.br

datum dbm_nextkey(DBM *\fP\fIdb\fP\fB);

.br

DBM *dbm_open(const char *\fP\fIfile\fP\fB, int\fP \fIopen_flags\fP\fB,

mode_t\fP \fIfile_mode\fP\fB);

.br

int dbm_store(DBM *\fP\fIdb\fP\fB, datum\fP \fIkey\fP\fB, datum\fP

\fIcontent\fP\fB, int\fP

\fIstore_mode\fP\fB);

.br

\fP

.SH DESCRIPTION

.LP

These functions create, access, and modify a database.

.LP

A \fBdatum\fP consists of at least two members, \fIdptr\fP and \fIdsize\fP.

The \fIdptr\fP member points to an object that

is \fIdsize\fP bytes in length. Arbitrary binary data, as well as

character strings, may be stored in the object pointed to by

\fIdptr\fP.

.LP

The database is stored in two files. One file is a directory containing

a bitmap of keys and has \fB.dir\fP as its suffix. The

second file contains all data and has \fB.pag\fP as its suffix.

.LP

The \fIdbm_open\fP() function shall open a database. The \fIfile\fP

argument to the function is the pathname of the database.

The function opens two files named \fIfile\fP\fB.dir\fP and \fIfile\fP\fB.pag\fP.

The \fIopen_flags\fP argument has the same

meaning as the \fIflags\fP argument of \fIopen\fP() except that a

database opened for

write-only access opens the files for read and write access and the

behavior of the O_APPEND flag is unspecified. The

\fIfile_mode\fP argument has the same meaning as the third argument

of \fIopen\fP().

.LP

The \fIdbm_close\fP() function shall close a database. The application

shall ensure that argument \fIdb\fP is a pointer to a

\fBdbm\fP structure that has been returned from a call to \fIdbm_open\fP().

.LP

These database functions shall support an internal block size large

enough to support key/content pairs of at least 1023

bytes.

.LP

The \fIdbm_fetch\fP() function shall read a record from a database.

The argument \fIdb\fP is a pointer to a database structure

that has been returned from a call to \fIdbm_open\fP(). The argument

\fIkey\fP is a \fBdatum\fP that has been initialized by the

application to the value of the key that matches the key of the record

the program is fetching.

.LP

The \fIdbm_store\fP() function shall write a record to a database.

The argument \fIdb\fP is a pointer to a database structure

that has been returned from a call to \fIdbm_open\fP(). The argument

\fIkey\fP is a \fBdatum\fP that has been initialized by the

application to the value of the key that identifies (for subsequent

reading, writing, or deleting) the record the application is

writing. The argument \fIcontent\fP is a \fBdatum\fP that has been

initialized by the application to the value of the record the

program is writing. The argument \fIstore_mode\fP controls whether

\fIdbm_store\fP() replaces any pre-existing record that has

the same key that is specified by the \fIkey\fP argument. The application

shall set \fIstore_mode\fP to either DBM_INSERT or

DBM_REPLACE. If the database contains a record that matches the \fIkey\fP

argument and \fIstore_mode\fP is DBM_REPLACE, the

existing record shall be replaced with the new record. If the database

contains a record that matches the \fIkey\fP argument and

\fIstore_mode\fP is DBM_INSERT, the existing record shall be left

unchanged and the new record ignored. If the database does not

contain a record that matches the \fIkey\fP argument and \fIstore_mode\fP

is either DBM_INSERT or DBM_REPLACE, the new record

shall be inserted in the database.

.LP

If the sum of a key/content pair exceeds the internal block size,

the result is unspecified. Moreover, the application shall

ensure that all key/content pairs that hash together fit on a single

block. The \fIdbm_store\fP() function shall return an error

in the event that a disk block fills with inseparable data.

.LP

The \fIdbm_delete\fP() function shall delete a record and its key

from the database. The argument \fIdb\fP is a pointer to a

database structure that has been returned from a call to \fIdbm_open\fP().

The argument \fIkey\fP is a \fBdatum\fP that has been

initialized by the application to the value of the key that identifies

the record the program is deleting.

.LP

The \fIdbm_firstkey\fP() function shall return the first key in the

database. The argument \fIdb\fP is a pointer to a database

structure that has been returned from a call to \fIdbm_open\fP().

.LP

The \fIdbm_nextkey\fP() function shall return the next key in the

database. The argument \fIdb\fP is a pointer to a database

structure that has been returned from a call to \fIdbm_open\fP().

The application shall ensure that the \fIdbm_firstkey\fP()

function is called before calling \fIdbm_nextkey\fP(). Subsequent

calls to \fIdbm_nextkey\fP() return the next key until all of

the keys in the database have been returned.

.LP

The \fIdbm_error\fP() function shall return the error condition of

the database. The argument \fIdb\fP is a pointer to a

database structure that has been returned from a call to \fIdbm_open\fP().

.LP

The \fIdbm_clearerr\fP() function shall clear the error condition

of the database. The argument \fIdb\fP is a pointer to a

database structure that has been returned from a call to \fIdbm_open\fP().

.LP

The \fIdptr\fP pointers returned by these functions may point into

static storage that may be changed by subsequent calls.

.LP

These functions need not be reentrant. A function that is not required

to be reentrant is not required to be thread-safe.

.SH RETURN VALUE

.LP

The \fIdbm_store\fP() and \fIdbm_delete\fP() functions shall return

0 when they succeed and a negative value when they

fail.

.LP

The \fIdbm_store\fP() function shall return 1 if it is called with

a \fIflags\fP value of DBM_INSERT and the function finds an

existing record with the same key.

.LP

The \fIdbm_error\fP() function shall return 0 if the error condition

is not set and return a non-zero value if the error

condition is set.

.LP

The return value of \fIdbm_clearerr\fP() is unspecified.

.LP

The \fIdbm_firstkey\fP() and \fIdbm_nextkey\fP() functions shall return

a key \fBdatum\fP. When the end of the database is

reached, the \fIdptr\fP member of the key is a null pointer. If an

error is detected, the \fIdptr\fP member of the key shall be a

null pointer and the error condition of the database shall be set.

.LP

The \fIdbm_fetch\fP() function shall return a content \fBdatum\fP.

If no record in the database matches the key or if an error

condition has been detected in the database, the \fIdptr\fP member

of the content shall be a null pointer.

.LP

The \fIdbm_open\fP() function shall return a pointer to a database

structure. If an error is detected during the operation,

\fIdbm_open\fP() shall return a ( \fBDBM *\fP)0.

.SH ERRORS

.LP

No errors are defined.

.LP

\fIThe following sections are informative.\fP

.SH EXAMPLES

.LP

None.

.SH APPLICATION USAGE

.LP

The following code can be used to traverse the database:

.sp

.RS

.nf

\fBfor(key = dbm_firstkey(db); key.dptr != NULL; key = dbm_nextkey(db))

\fP

.fi

.RE

.LP

The \fIdbm_\fP* functions provided in this library should not be confused

in any way with those of a general-purpose database

management system. These functions do not provide for multiple search

keys per entry, they do not protect against multi-user access

(in other words they do not lock records or files), and they do not

provide the many other useful database functions that are found

in more robust database management systems. Creating and updating

databases by use of these functions is relatively slow because of

data copies that occur upon hash collisions. These functions are useful

for applications requiring fast lookup of relatively static

information that is to be indexed by a single key.

.LP

Note that a strictly conforming application is extremely limited by

these functions: since there is no way to determine that the

keys in use do not all hash to the same value (although that would

be rare), a strictly conforming application cannot be guaranteed

that it can store more than one block's worth of data in the database.

As long as a key collision does not occur, additional data

may be stored, but because there is no way to determine whether an

error is due to a key collision or some other error condition (

\fIdbm_error\fP() being effectively a Boolean), once an error is detected,

the application is effectively limited to guessing what

the error might be if it wishes to continue using these functions.

.LP

The \fIdbm_delete\fP() function need not physically reclaim file space,

although it does make it available for reuse by the

database.

.LP

After calling \fIdbm_store\fP() or \fIdbm_delete\fP() during a pass

through the keys by \fIdbm_firstkey\fP() and

\fIdbm_nextkey\fP(), the application should reset the database by

calling \fIdbm_firstkey\fP() before again calling

\fIdbm_nextkey\fP(). The contents of these files are unspecified and

may not be portable.

.SH RATIONALE

.LP

None.

.SH FUTURE DIRECTIONS

.LP

None.

.SH SEE ALSO

.LP

\fIopen\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,

\fI<ndbm.h>\fP

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group. In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.opengroup.org/unix/online.html .