anydbm_file.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

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.\" ========================================================================
.\"
.IX Title "AnyDBM_File 3"
.TH AnyDBM_File 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.SH "NAME"
AnyDBM_File \- provide framework for multiple DBMs
.PP
NDBM_File, DB_File, GDBM_File, SDBM_File, ODBM_File \- various DBM implementations
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use AnyDBM_File;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module is a \*(L"pure virtual base class\*(R"\-\-it has nothing of its own.
It's just there to inherit from one of the various \s-1DBM\s0 packages.  It
prefers ndbm for compatibility reasons with Perl 4, then Berkeley \s-1DB\s0 (See
DB_File), \s-1GDBM\s0, \s-1SDBM\s0 (which is always there\*(--it comes with Perl), and
finally \s-1ODBM\s0.   This way old programs that used to use \s-1NDBM\s0 via \fIdbmopen()\fR
can still do so, but new ones can reorder \f(CW@ISA:\fR
.PP
.Vb 2
\&    BEGIN { @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File) }
\&    use AnyDBM_File;
.Ve
.PP
Having multiple \s-1DBM\s0 implementations makes it trivial to copy database formats:
.PP
.Vb 4
\&    use POSIX; use NDBM_File; use DB_File;
\&    tie %newhash,  \*(AqDB_File\*(Aq, $new_filename, O_CREAT|O_RDWR;
\&    tie %oldhash,  \*(AqNDBM_File\*(Aq, $old_filename, 1, 0;
\&    %newhash = %oldhash;
.Ve
.Sh "\s-1DBM\s0 Comparisons"
.IX Subsection "DBM Comparisons"
Here's a partial table of features the different packages offer:
.PP
.Vb 10
\&                         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
.Ve
.IP "[0]" 4
.IX Item "[0]"
on mixed universe machines, may be in the bsd compat library,
which is often shunned.
.IP "[1]" 4
.IX Item "[1]"
Can be trimmed if you compile for one access method.
.IP "[2]" 4
.IX Item "[2]"
See DB_File. 
Requires symbolic links.
.IP "[3]" 4
.IX Item "[3]"
By default, but can be redefined.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIdbm\fR\|(3), \fIndbm\fR\|(3), \fIDB_File\fR\|(3), perldbmfilter