Help-Site Computer Manuals
Software
Hardware
Programming
Networking
  Algorithms & Data Structures   Programming Languages   Revision Control
  Protocols
  Cameras   Computers   Displays   Keyboards & Mice   Motherboards   Networking   Printers & Scanners   Storage
  Windows   Linux & Unix   Mac

ODBM_File
Tied access to odbm files

ODBM_File - Tied access to odbm files


NAME

ODBM_File - Tied access to odbm files


SYNOPSIS


 use Fcntl;   # For O_RDWR, O_CREAT, etc.

 use ODBM_File;

  # Now read and change the hash

  $h{newkey} = newvalue;

  print $h{oldkey}; 

  ...

  untie %h;


DESCRIPTION

ODBM_File establishes a connection between a Perl hash variable and a file in ODBM_File format;. You can manipulate the data in the file just as if it were in a Perl hash, but when your program exits, the data will remain in the file, to be used the next time your program runs.

Use ODBM_File with the Perl built-in tie function to establish the connection between the variable and the file. The arguments to tie should be:

  1. The hash variable you want to tie.

  2. The string "ODBM_File". (Ths tells Perl to use the ODBM_File package to perform the functions of the hash.)

  3. The name of the file you want to tie to the hash.

  4. Flags. Use one of:
    O_RDONLY
    Read-only access to the data in the file.

    O_WRONLY
    Write-only access to the data in the file.

    O_RDWR
    Both read and write access.

    If you want to create the file if it does not exist, add O_CREAT to any of these, as in the example. If you omit O_CREAT and the file does not already exist, the tie call will fail.

  5. The default permissions to use if a new file is created. The actual permissions will be modified by the user's umask, so you should probably use 0666 here. (See perlfunc/umask.)


DIAGNOSTICS

On failure, the tie call returns an undefined value and probably sets $! to contain the reason the file could not be tied.

odbm store returned -1, errno 22, key "..." at ...

This warning is emmitted when you try to store a key or a value that is too long. It means that the change was not recorded in the database. See BUGS AND WARNINGS below.


BUGS AND WARNINGS

There are a number of limits on the size of the data that you can store in the ODBM file. The most important is that the length of a key, plus the length of its associated value, may not exceed 1008 bytes.

See perlfunc/tie, perldbmfilter, Fcntl

Programminig
Wy
Wy
yW
Wy
Programming
Wy
Wy
Wy
Wy