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Annotation of 43BSDTahoe/man/man3/dbm.3, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 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: .\"    @(#)dbm.3x      6.3 (Berkeley) 5/12/86
        !             6: .\"
        !             7: .TH DBM 3X  "May 12, 1986"
        !             8: .UC 4
        !             9: .SH NAME
        !            10: dbminit, fetch, store, delete, firstkey, nextkey \- data base subroutines
        !            11: .SH SYNOPSIS
        !            12: .nf
        !            13: .PP
        !            14: .B "#include <dbm.h>"
        !            15: .PP
        !            16: .B typedef struct {
        !            17: .B "   char *dptr;"
        !            18: .B "   int dsize;"
        !            19: .B } datum;
        !            20: .PP
        !            21: .B dbminit(file)
        !            22: .B char *file;
        !            23: .PP
        !            24: .B datum fetch(key)
        !            25: .B datum key;
        !            26: .PP
        !            27: .B store(key, content)
        !            28: .B datum key, content;
        !            29: .PP
        !            30: .B delete(key)
        !            31: .B datum key;
        !            32: .PP
        !            33: .B datum firstkey()
        !            34: .PP
        !            35: .B datum nextkey(key)
        !            36: .B datum key;
        !            37: .SH DESCRIPTION
        !            38: .ft B
        !            39: Note: the dbm library has been superceded by ndbm(3),
        !            40: and is now implemented using ndbm.
        !            41: .ft R
        !            42: These functions maintain key/content pairs in a data base.
        !            43: The functions will handle very large (a billion blocks)
        !            44: databases and will access a keyed item in one or two file system accesses.
        !            45: The functions are obtained with the loader option
        !            46: .BR \-ldbm .
        !            47: .PP
        !            48: .IR Key s
        !            49: and
        !            50: .IR content s
        !            51: are described by the
        !            52: .I datum
        !            53: typedef.  A
        !            54: .I datum
        !            55: specifies a string of
        !            56: .I dsize
        !            57: bytes pointed to by
        !            58: .I dptr.
        !            59: Arbitrary binary data, as well as normal ASCII strings, are allowed.
        !            60: The data base is stored in two files.
        !            61: One file is a directory containing a bit map and has `.dir' as its suffix.
        !            62: The second file contains all data and has `.pag' as its suffix.
        !            63: .PP
        !            64: Before a database can be accessed, it must be opened by
        !            65: .I dbminit.
        !            66: At the time of this call, the files
        !            67: .IB file .dir
        !            68: and
        !            69: .IB file .pag
        !            70: must exist.
        !            71: (An empty database is created by creating zero-length
        !            72: `.dir' and `.pag' files.)
        !            73: .PP
        !            74: Once open, the data stored under a key is accessed by
        !            75: .I fetch
        !            76: and data is placed under a key by
        !            77: .IR store .
        !            78: A key (and its associated contents) is deleted by
        !            79: .IR delete .
        !            80: A linear pass through all keys in a database may be made,
        !            81: in an (apparently) random order, by use of
        !            82: .I firstkey
        !            83: and
        !            84: .IR nextkey .
        !            85: .I Firstkey
        !            86: will return the first key in the database.  With any key
        !            87: .I nextkey
        !            88: will return the next key in the database.
        !            89: This code will traverse the data base:
        !            90: .IP
        !            91: .B for
        !            92: (key = firstkey(); key.dptr != NULL; key = nextkey(key))
        !            93: .SH DIAGNOSTICS
        !            94: All functions that return an
        !            95: .I int
        !            96: indicate errors with negative values.  A zero return indicates ok.
        !            97: Routines that return a
        !            98: .I datum
        !            99: indicate errors with a null (0)
        !           100: .I dptr.
        !           101: .SH SEE ALSO
        !           102: ndbm(3)
        !           103: .SH BUGS
        !           104: The `.pag' file will contain holes so that its apparent size is about
        !           105: four times its actual content.  Older UNIX systems may create real
        !           106: file blocks for these holes when touched.  These files cannot be copied
        !           107: by normal means (cp, cat, tp, tar, ar) without filling in the holes.
        !           108: .PP
        !           109: .I Dptr
        !           110: pointers returned by these subroutines point into static storage
        !           111: that is changed by subsequent calls.
        !           112: .PP
        !           113: The sum of the sizes of a key/content pair must not exceed
        !           114: the internal block size (currently 1024 bytes).
        !           115: Moreover all key/content pairs that hash together must fit on a single block.
        !           116: .I Store
        !           117: will return an error in the event that a disk block fills with inseparable data.
        !           118: .PP
        !           119: .I Delete
        !           120: does not physically reclaim file space,
        !           121: although it does make it available for reuse.
        !           122: .PP
        !           123: The order of keys presented by
        !           124: .I firstkey
        !           125: and
        !           126: .I nextkey
        !           127: depends on a hashing function, not on anything interesting.

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