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Annotation of 43BSDReno/lib/libc/gen/ndbm.3, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1985 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)ndbm.3      6.8 (Berkeley) 1/2/90
        !             6: .\"
        !             7: .TH NDBM 3  "January 2, 1990"
        !             8: .UC 6
        !             9: .SH NAME
        !            10: dbm_open, dbm_close, dbm_fetch, dbm_store, dbm_delete, dbm_firstkey, dbm_nextkey, dbm_error, dbm_clearerr \- data base subroutines
        !            11: .SH SYNOPSIS
        !            12: .nf
        !            13: .PP
        !            14: .ft B
        !            15: #include <ndbm.h>
        !            16: .PP
        !            17: .ft B
        !            18: typedef struct {
        !            19:     char *dptr;
        !            20:     int dsize;
        !            21: } datum;
        !            22: .PP
        !            23: .ft B
        !            24: DBM *dbm_open(file, flags, mode)
        !            25:     char *file;
        !            26:     int flags, mode;
        !            27: .PP
        !            28: .ft B
        !            29: void dbm_close(db)
        !            30:     DBM *db;
        !            31: .PP
        !            32: .ft B
        !            33: datum dbm_fetch(db, key)
        !            34:     DBM *db;
        !            35:     datum key;
        !            36: .PP
        !            37: .ft B
        !            38: int dbm_store(db, key, content, flags)
        !            39:     DBM *db;
        !            40:     datum key, content;
        !            41:     int flags;
        !            42: .PP
        !            43: .ft B
        !            44: int dbm_delete(db, key)
        !            45:     DBM *db;
        !            46:     datum key;
        !            47: .PP
        !            48: .ft B
        !            49: datum dbm_firstkey(db)
        !            50:     DBM *db;
        !            51: .PP
        !            52: .ft B
        !            53: datum dbm_nextkey(db)
        !            54:     DBM *db;
        !            55: .PP
        !            56: .ft B
        !            57: int dbm_error(db)
        !            58:     DBM *db;
        !            59: .PP
        !            60: .ft B
        !            61: int dbm_clearerr(db)
        !            62:     DBM *db;
        !            63: .SH DESCRIPTION
        !            64: These functions maintain key/content pairs in a data base.
        !            65: The functions will handle very large (a billion blocks)
        !            66: databases and will access a keyed item in one or two file system accesses.
        !            67: This package replaces the earlier
        !            68: .IR dbm (3x)
        !            69: library, which managed only a single database.
        !            70: .PP
        !            71: .IR Key s
        !            72: and
        !            73: .IR content s
        !            74: are described by the
        !            75: .I datum
        !            76: typedef.  A
        !            77: .I datum
        !            78: specifies a string of
        !            79: .I dsize
        !            80: bytes pointed to by
        !            81: .I dptr.
        !            82: Arbitrary binary data, as well as normal ASCII strings, are allowed.
        !            83: The data base is stored in two files.
        !            84: One file is a directory containing a bit map and has `.dir' as its suffix.
        !            85: The second file contains all data and has `.pag' as its suffix.
        !            86: .PP
        !            87: Before a database can be accessed, it must be opened by
        !            88: .IR dbm_open .
        !            89: This will open and/or create the files
        !            90: .IB file .dir
        !            91: and
        !            92: .IB file .pag
        !            93: depending on the flags parameter (see
        !            94: .IR open (2)).
        !            95: .PP
        !            96: Once open, the data stored under a key is accessed by
        !            97: .I dbm_fetch
        !            98: and data is placed under a key by
        !            99: .IR dbm_store .
        !           100: The
        !           101: .I flags
        !           102: field can be either
        !           103: .B DBM_INSERT
        !           104: or
        !           105: .B DBM_REPLACE.
        !           106: .B DBM_INSERT
        !           107: will only insert new entries into the database and will not
        !           108: change an existing entry with the same key.
        !           109: .B DBM_REPLACE
        !           110: will replace an existing entry if it has the same key.
        !           111: A key (and its associated contents) is deleted by
        !           112: .IR dbm_delete .
        !           113: A linear pass through all keys in a database may be made,
        !           114: in an (apparently) random order, by use of
        !           115: .I dbm_firstkey
        !           116: and
        !           117: .IR dbm_nextkey .
        !           118: .I Dbm_firstkey
        !           119: will return the first key in the database.
        !           120: .I Dbm_nextkey
        !           121: will return the next key in the database.
        !           122: This code will traverse the data base:
        !           123: .IP
        !           124: .B for
        !           125: (key = dbm_firstkey(db); key.dptr != NULL; key = dbm_nextkey(db))
        !           126: .PP
        !           127: .I Dbm_error
        !           128: returns non-zero when an error has occurred reading or writing the database.
        !           129: .I Dbm_clearerr
        !           130: resets the error condition on the named database.
        !           131: .SH DIAGNOSTICS
        !           132: All functions that return an
        !           133: .I int
        !           134: indicate errors with negative values.  A zero return indicates ok.
        !           135: Routines that return a
        !           136: .I datum
        !           137: indicate errors with a null (0)
        !           138: .I dptr.
        !           139: If
        !           140: .IR dbm_store
        !           141: called with a
        !           142: .I flags
        !           143: value of
        !           144: .B DBM_INSERT
        !           145: finds an existing entry with the same key
        !           146: it returns 1.
        !           147: .SH BUGS
        !           148: The `.pag' file will contain holes so that its apparent size is about
        !           149: four times its actual content.  Older UNIX systems may create real
        !           150: file blocks for these holes when touched.  These files cannot be copied
        !           151: by normal means (cp, cat, tp, tar, ar) without filling in the holes.
        !           152: .PP
        !           153: .I Dptr
        !           154: pointers returned by these subroutines point into static storage that is
        !           155: changed by subsequent calls.  This storage is not necessarily aligned;
        !           156: stored ``longs'', for example, should be copied to a properly aligned
        !           157: block of memory before being accessed.
        !           158: .PP
        !           159: The sum of the sizes of a key/content pair must not exceed
        !           160: the internal block size (currently 1024 bytes).
        !           161: Moreover all key/content pairs that hash together must fit on a single block.
        !           162: .I Dbm_store
        !           163: will return an error in the event that a disk block fills with inseparable data.
        !           164: .PP
        !           165: .I Dbm_delete
        !           166: does not physically reclaim file space,
        !           167: although it does make it available for reuse.
        !           168: .PP
        !           169: The order of keys presented by
        !           170: .I dbm_firstkey
        !           171: and
        !           172: .I dbm_nextkey
        !           173: depends on a hashing function, not on anything interesting.
        !           174: .SH SEE ALSO
        !           175: dbm(3X)

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