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Annotation of cci/usr/src/man/man3/dbm.3x, revision 1.1

1.1     ! root        1: .TH DBM 3X  "19 January 1983"
        !             2: .UC 4
        !             3: .SH NAME
        !             4: dbminit, fetch, store, delete, firstkey, nextkey \- data base subroutines
        !             5: .SH SYNOPSIS
        !             6: .nf
        !             7: .PP
        !             8: .B typedef struct {
        !             9: .B "   char *dptr;"
        !            10: .B "   int dsize;"
        !            11: .B } datum;
        !            12: .PP
        !            13: .B dbminit(file)
        !            14: .B char *file;
        !            15: .PP
        !            16: .B datum fetch(key)
        !            17: .B datum key;
        !            18: .PP
        !            19: .B store(key, content)
        !            20: .B datum key, content;
        !            21: .PP
        !            22: .B delete(key)
        !            23: .B datum key;
        !            24: .PP
        !            25: .B datum firstkey()
        !            26: .PP
        !            27: .B datum nextkey(key)
        !            28: .B datum key;
        !            29: .SH DESCRIPTION
        !            30: These functions maintain key/content pairs in a data base.
        !            31: The functions will handle very large (a billion blocks)
        !            32: databases and will access a keyed item in one or two file system accesses.
        !            33: The functions are obtained with the loader option
        !            34: .BR \-ldbm .
        !            35: .PP
        !            36: .IR Key s
        !            37: and
        !            38: .IR content s
        !            39: are described by the
        !            40: .I datum
        !            41: typedef.  A
        !            42: .I datum
        !            43: specifies a string of
        !            44: .I dsize
        !            45: bytes pointed to by
        !            46: .I dptr.
        !            47: Arbitrary binary data, as well as normal ASCII strings, are allowed.
        !            48: The data base is stored in two files.
        !            49: One file is a directory containing a bit map and has `.dir' as its suffix.
        !            50: The second file contains all data and has `.pag' as its suffix.
        !            51: .PP
        !            52: Before a database can be accessed, it must be opened by
        !            53: .I dbminit.
        !            54: At the time of this call, the files
        !            55: .IB file .dir
        !            56: and
        !            57: .IB file .pag
        !            58: must exist.
        !            59: (An empty database is created by creating zero-length
        !            60: `.dir' and `.pag' files.)
        !            61: .PP
        !            62: Once open, the data stored under a key is accessed by
        !            63: .I fetch
        !            64: and data is placed under a key by
        !            65: .IR store .
        !            66: A key (and its associated contents) is deleted by
        !            67: .IR delete .
        !            68: A linear pass through all keys in a database may be made,
        !            69: in an (apparently) random order, by use of
        !            70: .I firstkey
        !            71: and
        !            72: .IR nextkey .
        !            73: .I Firstkey
        !            74: will return the first key in the database.  With any key
        !            75: .I nextkey
        !            76: will return the next key in the database.
        !            77: This code will traverse the data base:
        !            78: .IP
        !            79: .B for
        !            80: (key = firstkey(); key.dptr != NULL; key = nextkey(key))
        !            81: .SH DIAGNOSTICS
        !            82: All functions that return an
        !            83: .I int
        !            84: indicate errors with negative values.  A zero return indicates ok.
        !            85: Routines that return a
        !            86: .I datum
        !            87: indicate errors with a null (0)
        !            88: .I dptr.
        !            89: .SH BUGS
        !            90: The `.pag' file will contain holes so that its apparent size is about
        !            91: four times its actual content.  Older UNIX systems may create real
        !            92: file blocks for these holes when touched.  These files cannot be copied
        !            93: by normal means (cp, cat, tp, tar, ar) without filling in the holes.
        !            94: .PP
        !            95: .I Dptr
        !            96: pointers returned by these subroutines point into static storage
        !            97: that is changed by subsequent calls.
        !            98: .PP
        !            99: The sum of the sizes of a key/content pair must not exceed
        !           100: the internal block size (currently 1024 bytes).
        !           101: Moreover all key/content pairs that hash together must fit on a single block.
        !           102: .I Store
        !           103: will return an error in the event that a disk block fills with inseparable data.
        !           104: .PP
        !           105: .I Delete
        !           106: does not physically reclaim file space,
        !           107: although it does make it available for reuse.
        !           108: .PP
        !           109: The order of keys presented by
        !           110: .I firstkey
        !           111: and
        !           112: .I nextkey
        !           113: depends on a hashing function, not on anything interesting.

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