README
1
2This package implements a superset of the hsearch and dbm/ndbm libraries.
3
4Test Programs:
5 All test programs which need key/data pairs expect them entered
6 with key and data on separate lines
7
8 tcreat3.c
9 Takes
10 bucketsize (bsize),
11 fill factor (ffactor), and
12 initial number of elements (nelem).
13 Creates a hash table named hashtest containing the
14 keys/data pairs entered from standard in.
15 thash4.c
16 Takes
17 bucketsize (bsize),
18 fill factor (ffactor),
19 initial number of elements (nelem)
20 bytes of cache (ncached), and
21 file from which to read data (fname)
22 Creates a table from the key/data pairs on standard in and
23 then does a read of each key/data in fname
24 tdel.c
25 Takes
26 bucketsize (bsize), and
27 fill factor (ffactor).
28 file from which to read data (fname)
29 Reads each key/data pair from fname and deletes the
30 key from the hash table hashtest
31 tseq.c
32 Reads the key/data pairs in the file hashtest and writes them
33 to standard out.
34 tread2.c
35 Takes
36 butes of cache (ncached).
37 Reads key/data pairs from standard in and looks them up
38 in the file hashtest.
39 tverify.c
40 Reads key/data pairs from standard in, looks them up
41 in the file hashtest, and verifies that the data is
42 correct.
43
44NOTES:
45
46The man page ../man/db.3 explains the interface to the hashing system.
47The file hash.ps is a postscript copy of a paper explaining
48the history, implementation, and performance of the hash package.
49
50"bugs" or idiosyncracies
51
52If you have a lot of overflows, it is possible to run out of overflow
53pages. Currently, this will cause a message to be printed on stderr.
54Eventually, this will be indicated by a return error code.
55
56If you are using the ndbm interface and exit without flushing or closing the
57file, you may lose updates since the package buffers all writes. Also,
58the db interface only creates a single database file. To avoid overwriting
59the user's original file, the suffix ".db" is appended to the file name
60passed to dbm_open. Additionally, if your code "knows" about the historic
61.dir and .pag files, it will break.
62
63There is a fundamental difference between this package and the old hsearch.
64Hsearch requires the user to maintain the keys and data in the application's
65allocated memory while hash takes care of all storage management. The down
66side is that the byte strings passed in the ENTRY structure must be null
67terminated (both the keys and the data).
68