Source code of Windows XP (NT5)
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package AnyDBM_File;
use vars qw(@ISA); @ISA = qw(NDBM_File DB_File GDBM_File SDBM_File ODBM_File) unless @ISA;
my $mod; for $mod (@ISA) { if (eval "require $mod") { @ISA = ($mod); # if we leave @ISA alone, warnings abound return 1; } }
die "No DBM package was successfully found or installed"; #return 0;
=head1 NAME
AnyDBM_File - provide framework for multiple DBMs
NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File - various DBM implementations
=head1 SYNOPSIS
use AnyDBM_File;
=head1 DESCRIPTION
This module is a "pure virtual base class"--it has nothing of its own. It's just there to inherit from one of the various DBM packages. It prefers ndbm for compatibility reasons with Perl 4, then Berkeley DB (See L<DB_File>), GDBM, SDBM (which is always there--it comes with Perl), and finally ODBM. This way old programs that used to use NDBM via dbmopen() can still do so, but new ones can reorder @ISA:
BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) } use AnyDBM_File;
Having multiple DBM implementations makes it trivial to copy database formats:
use POSIX; use NDBM_File; use DB_File; tie %newhash, 'DB_File', $new_filename, O_CREAT|O_RDWR; tie %oldhash, 'NDBM_File', $old_filename, 1, 0; %newhash = %oldhash;
=head2 DBM Comparisons
Here's a partial table of features the different packages offer:
odbm ndbm sdbm gdbm bsd-db ---- ---- ---- ---- ------ Linkage comes w/ perl yes yes yes yes yes Src comes w/ perl no no yes no no Comes w/ many unix os yes yes[0] no no no Builds ok on !unix ? ? yes yes ? Code Size ? ? small big big Database Size ? ? small big? ok[1] Speed ? ? slow ok fast FTPable no no yes yes yes Easy to build N/A N/A yes yes ok[2] Size limits 1k 4k 1k[3] none none Byte-order independent no no no no yes Licensing restrictions ? ? no yes no
=over 4
=item [0]
on mixed universe machines, may be in the bsd compat library, which is often shunned.
=item [1]
Can be trimmed if you compile for one access method.
=item [2]
See L<DB_File>. Requires symbolic links.
=item [3]
By default, but can be redefined.
=back
=head1 SEE ALSO
dbm(3), ndbm(3), DB_File(3)
=cut
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