1DBM_CLEARERR(P) POSIX Programmer's Manual DBM_CLEARERR(P)
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6 dbm_clearerr, dbm_close, dbm_delete, dbm_error, dbm_fetch,
7 dbm_firstkey, dbm_nextkey, dbm_open, dbm_store - database functions
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10 #include <ndbm.h>
11 int dbm_clearerr(DBM *db);
13 void dbm_close(DBM *db);
14 int dbm_delete(DBM *db, datum key);
15 int dbm_error(DBM *db);
16 datum dbm_fetch(DBM *db, datum key);
17 datum dbm_firstkey(DBM *db);
18 datum dbm_nextkey(DBM *db);
19 DBM *dbm_open(const char *file, int open_flags, mode_t file_mode);
20 int dbm_store(DBM *db, datum key, datum content, int store_mode);
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24 These functions create, access, and modify a database.
25 A datum consists of at least two members, dptr and dsize. The dptr
27 member points to an object that is dsize bytes in length. Arbitrary
28 binary data, as well as character strings, may be stored in the object
29 pointed to by dptr.
30 The database is stored in two files. One file is a directory containing
32 a bitmap of keys and has .dir as its suffix. The second file contains
33 all data and has .pag as its suffix.
34 The dbm_open() function shall open a database. The file argument to the
36 function is the pathname of the database. The function opens two files
37 named file.dir and file.pag. The open_flags argument has the same
38 meaning as the flags argument of open() except that a database opened
39 for write-only access opens the files for read and write access and the
40 behavior of the O_APPEND flag is unspecified. The file_mode argument
41 has the same meaning as the third argument of open().
42 The dbm_close() function shall close a database. The application shall
44 ensure that argument db is a pointer to a dbm structure that has been
45 returned from a call to dbm_open().
46 These database functions shall support an internal block size large
48 enough to support key/content pairs of at least 1023 bytes.
49 The dbm_fetch() function shall read a record from a database. The
51 argument db is a pointer to a database structure that has been returned
52 from a call to dbm_open(). The argument key is a datum that has been
53 initialized by the application to the value of the key that matches the
54 key of the record the program is fetching.
55 The dbm_store() function shall write a record to a database. The argu‐
57 ment db is a pointer to a database structure that has been returned
58 from a call to dbm_open(). The argument key is a datum that has been
59 initialized by the application to the value of the key that identifies
60 (for subsequent reading, writing, or deleting) the record the applica‐
61 tion is writing. The argument content is a datum that has been initial‐
62 ized by the application to the value of the record the program is writ‐
63 ing. The argument store_mode controls whether dbm_store() replaces any
64 pre-existing record that has the same key that is specified by the key
65 argument. The application shall set store_mode to either DBM_INSERT or
66 DBM_REPLACE. If the database contains a record that matches the key
67 argument and store_mode is DBM_REPLACE, the existing record shall be
68 replaced with the new record. If the database contains a record that
69 matches the key argument and store_mode is DBM_INSERT, the existing
70 record shall be left unchanged and the new record ignored. If the data‐
71 base does not contain a record that matches the key argument and
72 store_mode is either DBM_INSERT or DBM_REPLACE, the new record shall be
73 inserted in the database.
74 If the sum of a key/content pair exceeds the internal block size, the
76 result is unspecified. Moreover, the application shall ensure that all
77 key/content pairs that hash together fit on a single block. The
78 dbm_store() function shall return an error in the event that a disk
79 block fills with inseparable data.
80 The dbm_delete() function shall delete a record and its key from the
82 database. The argument db is a pointer to a database structure that has
83 been returned from a call to dbm_open(). The argument key is a datum
84 that has been initialized by the application to the value of the key
85 that identifies the record the program is deleting.
86 The dbm_firstkey() function shall return the first key in the database.
88 The argument db is a pointer to a database structure that has been
89 returned from a call to dbm_open().
90 The dbm_nextkey() function shall return the next key in the database.
92 The argument db is a pointer to a database structure that has been
93 returned from a call to dbm_open(). The application shall ensure that
94 the dbm_firstkey() function is called before calling dbm_nextkey().
95 Subsequent calls to dbm_nextkey() return the next key until all of the
96 keys in the database have been returned.
97 The dbm_error() function shall return the error condition of the data‐
99 base. The argument db is a pointer to a database structure that has
100 been returned from a call to dbm_open().
101 The dbm_clearerr() function shall clear the error condition of the
103 database. The argument db is a pointer to a database structure that has
104 been returned from a call to dbm_open().
105 The dptr pointers returned by these functions may point into static
107 storage that may be changed by subsequent calls.
108 These functions need not be reentrant. A function that is not required
110 to be reentrant is not required to be thread-safe.
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113 The dbm_store() and dbm_delete() functions shall return 0 when they
114 succeed and a negative value when they fail.
115 The dbm_store() function shall return 1 if it is called with a flags
117 value of DBM_INSERT and the function finds an existing record with the
118 same key.
119 The dbm_error() function shall return 0 if the error condition is not
121 set and return a non-zero value if the error condition is set.
122 The return value of dbm_clearerr() is unspecified.
124 The dbm_firstkey() and dbm_nextkey() functions shall return a key
126 datum. When the end of the database is reached, the dptr member of the
127 key is a null pointer. If an error is detected, the dptr member of the
128 key shall be a null pointer and the error condition of the database
129 shall be set.
130 The dbm_fetch() function shall return a content datum. If no record in
132 the database matches the key or if an error condition has been detected
133 in the database, the dptr member of the content shall be a null
134 pointer.
135 The dbm_open() function shall return a pointer to a database structure.
137 If an error is detected during the operation, dbm_open() shall return a
138 ( DBM *)0.
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141 No errors are defined.
142 The following sections are informative.
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146 None.
147
149 The following code can be used to traverse the database:
150 for(key = dbm_firstkey(db); key.dptr != NULL; key = dbm_nextkey(db))
153 The dbm_* functions provided in this library should not be confused in
155 any way with those of a general-purpose database management system.
156 These functions do not provide for multiple search keys per entry, they
157 do not protect against multi-user access (in other words they do not
158 lock records or files), and they do not provide the many other useful
159 database functions that are found in more robust database management
160 systems. Creating and updating databases by use of these functions is
161 relatively slow because of data copies that occur upon hash collisions.
162 These functions are useful for applications requiring fast lookup of
163 relatively static information that is to be indexed by a single key.
164 Note that a strictly conforming application is extremely limited by
166 these functions: since there is no way to determine that the keys in
167 use do not all hash to the same value (although that would be rare), a
168 strictly conforming application cannot be guaranteed that it can store
169 more than one block's worth of data in the database. As long as a key
170 collision does not occur, additional data may be stored, but because
171 there is no way to determine whether an error is due to a key collision
172 or some other error condition ( dbm_error() being effectively a Bool‐
173 ean), once an error is detected, the application is effectively limited
174 to guessing what the error might be if it wishes to continue using
175 these functions.
176 The dbm_delete() function need not physically reclaim file space,
178 although it does make it available for reuse by the database.
179 After calling dbm_store() or dbm_delete() during a pass through the
181 keys by dbm_firstkey() and dbm_nextkey(), the application should reset
182 the database by calling dbm_firstkey() before again calling dbm_nex‐
183 tkey(). The contents of these files are unspecified and may not be por‐
184 table.
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187 None.
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190 None.
191
193 open() , the Base Definitions volume of IEEE Std 1003.1-2001, <ndbm.h>
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196 Portions of this text are reprinted and reproduced in electronic form
197 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
198 -- Portable Operating System Interface (POSIX), The Open Group Base
199 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
200 Electrical and Electronics Engineers, Inc and The Open Group. In the
201 event of any discrepancy between this version and the original IEEE and
202 The Open Group Standard, the original IEEE and The Open Group Standard
203 is the referee document. The original Standard can be obtained online
204 at http://www.opengroup.org/unix/online.html .
205IEEE/The Open Group 2003 DBM_CLEARERR(P)