2 # Copyright (c) 1995-2000, Raphael Manfredi
4 # You may redistribute only under the same terms as Perl 5, as specified
5 # in the README file that comes with the distribution.
10 package Storable; @ISA = qw(Exporter DynaLoader);
12 @EXPORT = qw(store retrieve);
14 nstore store_fd nstore_fd fd_retrieve
18 lock_store lock_nstore lock_retrieve
22 use vars qw($canonical $forgive_me $VERSION);
25 *AUTOLOAD = \&AutoLoader::AUTOLOAD; # Grrr...
28 # Use of Log::Agent is optional
31 eval "use Log::Agent";
36 # They might miss :flock in Fcntl
40 if (eval { require Fcntl; 1 } && exists $Fcntl::EXPORT_TAGS{'flock'}) {
41 Fcntl->import(':flock');
50 # Can't Autoload cleanly as this clashes 8.3 with &retrieve
51 sub retrieve_fd { &fd_retrieve } # Backward compatibility
53 # By default restricted hashes are downgraded on earlier perls.
55 $Storable::downgrade_restricted = 1;
56 $Storable::accept_future_minor = 1;
61 # Use of Log::Agent is optional. If it hasn't imported these subs then
62 # Autoloader will kindly supply our fallback implementation.
74 # Determine whether locking is possible, but only when needed.
77 sub CAN_FLOCK; my $CAN_FLOCK; sub CAN_FLOCK {
78 return $CAN_FLOCK if defined $CAN_FLOCK;
79 require Config; import Config;
82 $Config{'d_fcntl_can_lock'} ||
89 # To recognize the data files of the Perl module Storable,
90 # the following lines need to be added to the local magic(5) file,
91 # usually either /usr/share/misc/magic or /etc/magic.
93 0 string perl-store perl Storable(v0.6) data
94 >4 byte >0 (net-order %d)
95 >>4 byte &01 (network-ordered)
99 0 string pst0 perl Storable(v0.7) data
101 >>4 byte &01 (network-ordered)
102 >>4 byte =5 (major 2)
103 >>4 byte =4 (major 2)
104 >>5 byte >0 (minor %d)
110 return unless defined $header and length $header > 11;
112 if ($header =~ s/^perl-store//) {
113 die "Can't deal with version 0 headers";
114 } elsif ($header =~ s/^pst0//) {
117 # Assume it's a string.
118 my ($major, $minor, $bytelen) = unpack "C3", $header;
120 my $net_order = $major & 1;
122 @$result{qw(major minor netorder)} = ($major, $minor, $net_order);
124 return $result if $net_order;
126 # I assume that it is rare to find v1 files, so this is an intentionally
127 # inefficient way of doing it, to make the rest of the code constant.
129 delete $result->{minor};
130 $header = '.' . $header;
134 @$result{qw(byteorder intsize longsize ptrsize)} =
135 unpack "x3 A$bytelen C3", $header;
137 if ($major >= 2 and $minor >= 2) {
138 $result->{nvsize} = unpack "x6 x$bytelen C", $header;
146 # Store target object hierarchy, identified by a reference to its root.
147 # The stored object tree may later be retrieved to memory via retrieve.
148 # Returns undef if an I/O error occurred, in which case the file is
152 return _store(\&pstore, @_, 0);
158 # Same as store, but in network order.
161 return _store(\&net_pstore, @_, 0);
167 # Same as store, but flock the file first (advisory locking).
170 return _store(\&pstore, @_, 1);
176 # Same as nstore, but flock the file first (advisory locking).
179 return _store(\&net_pstore, @_, 1);
182 # Internal store to file routine
186 my ($file, $use_locking) = @_;
187 logcroak "not a reference" unless ref($self);
188 logcroak "wrong argument number" unless @_ == 2; # No @foo in arglist
191 open(FILE, ">>$file") || logcroak "can't write into $file: $!";
192 unless (&CAN_FLOCK) {
193 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
196 flock(FILE, LOCK_EX) ||
197 logcroak "can't get exclusive lock on $file: $!";
199 # Unlocking will happen when FILE is closed
201 open(FILE, ">$file") || logcroak "can't create $file: $!";
203 binmode FILE; # Archaic systems...
204 my $da = $@; # Don't mess if called from exception handler
206 # Call C routine nstore or pstore, depending on network order
207 eval { $ret = &$xsptr(*FILE, $self) };
208 close(FILE) or $ret = undef;
209 unlink($file) or warn "Can't unlink $file: $!\n" if $@ || !defined $ret;
210 logcroak $@ if $@ =~ s/\.?\n$/,/;
212 return $ret ? $ret : undef;
218 # Same as store, but perform on an already opened file descriptor instead.
219 # Returns undef if an I/O error occurred.
222 return _store_fd(\&pstore, @_);
228 # Same as store_fd, but in network order.
231 my ($self, $file) = @_;
232 return _store_fd(\&net_pstore, @_);
235 # Internal store routine on opened file descriptor
240 logcroak "not a reference" unless ref($self);
241 logcroak "too many arguments" unless @_ == 1; # No @foo in arglist
242 my $fd = fileno($file);
243 logcroak "not a valid file descriptor" unless defined $fd;
244 my $da = $@; # Don't mess if called from exception handler
246 # Call C routine nstore or pstore, depending on network order
247 eval { $ret = &$xsptr($file, $self) };
248 logcroak $@ if $@ =~ s/\.?\n$/,/;
249 local $\; print $file ''; # Autoflush the file if wanted
251 return $ret ? $ret : undef;
257 # Store oject and its hierarchy in memory and return a scalar
258 # containing the result.
261 _freeze(\&mstore, @_);
267 # Same as freeze but in network order.
270 _freeze(\&net_mstore, @_);
273 # Internal freeze routine
277 logcroak "not a reference" unless ref($self);
278 logcroak "too many arguments" unless @_ == 0; # No @foo in arglist
279 my $da = $@; # Don't mess if called from exception handler
281 # Call C routine mstore or net_mstore, depending on network order
282 eval { $ret = &$xsptr($self) };
283 logcroak $@ if $@ =~ s/\.?\n$/,/;
285 return $ret ? $ret : undef;
291 # Retrieve object hierarchy from disk, returning a reference to the root
292 # object of that tree.
301 # Same as retrieve, but with advisory locking.
307 # Internal retrieve routine
309 my ($file, $use_locking) = @_;
311 open(FILE, $file) || logcroak "can't open $file: $!";
312 binmode FILE; # Archaic systems...
314 my $da = $@; # Could be from exception handler
316 unless (&CAN_FLOCK) {
317 logcarp "Storable::lock_store: fcntl/flock emulation broken on $^O";
320 flock(FILE, LOCK_SH) || logcroak "can't get shared lock on $file: $!";
321 # Unlocking will happen when FILE is closed
323 eval { $self = pretrieve(*FILE) }; # Call C routine
325 logcroak $@ if $@ =~ s/\.?\n$/,/;
333 # Same as retrieve, but perform from an already opened file descriptor instead.
337 my $fd = fileno($file);
338 logcroak "not a valid file descriptor" unless defined $fd;
340 my $da = $@; # Could be from exception handler
341 eval { $self = pretrieve($file) }; # Call C routine
342 logcroak $@ if $@ =~ s/\.?\n$/,/;
350 # Recreate objects in memory from an existing frozen image created
351 # by freeze. If the frozen image passed is undef, return undef.
355 return undef unless defined $frozen;
357 my $da = $@; # Could be from exception handler
358 eval { $self = mretrieve($frozen) }; # Call C routine
359 logcroak $@ if $@ =~ s/\.?\n$/,/;
366 Storable - persistence for Perl data structures
371 store \%table, 'file';
372 $hashref = retrieve('file');
374 use Storable qw(nstore store_fd nstore_fd freeze thaw dclone);
377 nstore \%table, 'file';
378 $hashref = retrieve('file'); # There is NO nretrieve()
380 # Storing to and retrieving from an already opened file
381 store_fd \@array, \*STDOUT;
382 nstore_fd \%table, \*STDOUT;
383 $aryref = fd_retrieve(\*SOCKET);
384 $hashref = fd_retrieve(\*SOCKET);
386 # Serializing to memory
387 $serialized = freeze \%table;
388 %table_clone = %{ thaw($serialized) };
390 # Deep (recursive) cloning
391 $cloneref = dclone($ref);
394 use Storable qw(lock_store lock_nstore lock_retrieve)
395 lock_store \%table, 'file';
396 lock_nstore \%table, 'file';
397 $hashref = lock_retrieve('file');
401 The Storable package brings persistence to your Perl data structures
402 containing SCALAR, ARRAY, HASH or REF objects, i.e. anything that can be
403 conveniently stored to disk and retrieved at a later time.
405 It can be used in the regular procedural way by calling C<store> with
406 a reference to the object to be stored, along with the file name where
407 the image should be written.
409 The routine returns C<undef> for I/O problems or other internal error,
410 a true value otherwise. Serious errors are propagated as a C<die> exception.
412 To retrieve data stored to disk, use C<retrieve> with a file name.
413 The objects stored into that file are recreated into memory for you,
414 and a I<reference> to the root object is returned. In case an I/O error
415 occurs while reading, C<undef> is returned instead. Other serious
416 errors are propagated via C<die>.
418 Since storage is performed recursively, you might want to stuff references
419 to objects that share a lot of common data into a single array or hash
420 table, and then store that object. That way, when you retrieve back the
421 whole thing, the objects will continue to share what they originally shared.
423 At the cost of a slight header overhead, you may store to an already
424 opened file descriptor using the C<store_fd> routine, and retrieve
425 from a file via C<fd_retrieve>. Those names aren't imported by default,
426 so you will have to do that explicitly if you need those routines.
427 The file descriptor you supply must be already opened, for read
428 if you're going to retrieve and for write if you wish to store.
430 store_fd(\%table, *STDOUT) || die "can't store to stdout\n";
431 $hashref = fd_retrieve(*STDIN);
433 You can also store data in network order to allow easy sharing across
434 multiple platforms, or when storing on a socket known to be remotely
435 connected. The routines to call have an initial C<n> prefix for I<network>,
436 as in C<nstore> and C<nstore_fd>. At retrieval time, your data will be
437 correctly restored so you don't have to know whether you're restoring
438 from native or network ordered data. Double values are stored stringified
439 to ensure portability as well, at the slight risk of loosing some precision
440 in the last decimals.
442 When using C<fd_retrieve>, objects are retrieved in sequence, one
443 object (i.e. one recursive tree) per associated C<store_fd>.
445 If you're more from the object-oriented camp, you can inherit from
446 Storable and directly store your objects by invoking C<store> as
447 a method. The fact that the root of the to-be-stored tree is a
448 blessed reference (i.e. an object) is special-cased so that the
449 retrieve does not provide a reference to that object but rather the
450 blessed object reference itself. (Otherwise, you'd get a reference
451 to that blessed object).
455 The Storable engine can also store data into a Perl scalar instead, to
456 later retrieve them. This is mainly used to freeze a complex structure in
457 some safe compact memory place (where it can possibly be sent to another
458 process via some IPC, since freezing the structure also serializes it in
459 effect). Later on, and maybe somewhere else, you can thaw the Perl scalar
460 out and recreate the original complex structure in memory.
462 Surprisingly, the routines to be called are named C<freeze> and C<thaw>.
463 If you wish to send out the frozen scalar to another machine, use
464 C<nfreeze> instead to get a portable image.
466 Note that freezing an object structure and immediately thawing it
467 actually achieves a deep cloning of that structure:
469 dclone(.) = thaw(freeze(.))
471 Storable provides you with a C<dclone> interface which does not create
472 that intermediary scalar but instead freezes the structure in some
473 internal memory space and then immediately thaws it out.
475 =head1 ADVISORY LOCKING
477 The C<lock_store> and C<lock_nstore> routine are equivalent to
478 C<store> and C<nstore>, except that they get an exclusive lock on
479 the file before writing. Likewise, C<lock_retrieve> does the same
480 as C<retrieve>, but also gets a shared lock on the file before reading.
482 As with any advisory locking scheme, the protection only works if you
483 systematically use C<lock_store> and C<lock_retrieve>. If one side of
484 your application uses C<store> whilst the other uses C<lock_retrieve>,
485 you will get no protection at all.
487 The internal advisory locking is implemented using Perl's flock()
488 routine. If your system does not support any form of flock(), or if
489 you share your files across NFS, you might wish to use other forms
490 of locking by using modules such as LockFile::Simple which lock a
491 file using a filesystem entry, instead of locking the file descriptor.
495 The heart of Storable is written in C for decent speed. Extra low-level
496 optimizations have been made when manipulating perl internals, to
497 sacrifice encapsulation for the benefit of greater speed.
499 =head1 CANONICAL REPRESENTATION
501 Normally, Storable stores elements of hashes in the order they are
502 stored internally by Perl, i.e. pseudo-randomly. If you set
503 C<$Storable::canonical> to some C<TRUE> value, Storable will store
504 hashes with the elements sorted by their key. This allows you to
505 compare data structures by comparing their frozen representations (or
506 even the compressed frozen representations), which can be useful for
507 creating lookup tables for complicated queries.
509 Canonical order does not imply network order; those are two orthogonal
512 =head1 CODE REFERENCES
514 Since Storable version 2.05, CODE references may be serialized with
515 the help of L<B::Deparse>. To enable this feature, set
516 C<$Storable::Deparse> to a true value. To enable deserializazion,
517 C<$Storable::Eval> should be set to a true value. Be aware that
518 deserialization is done through C<eval>, which is dangerous if the
519 Storable file contains malicious data. You can set C<$Storable::Eval>
520 to a subroutine reference which would be used instead of C<eval>. See
521 below for an example using a L<Safe> compartment for deserialization
524 =head1 FORWARD COMPATIBILITY
526 This release of Storable can be used on a newer version of Perl to
527 serialize data which is not supported by earlier Perls. By default,
528 Storable will attempt to do the right thing, by C<croak()>ing if it
529 encounters data that it cannot deserialize. However, the defaults
530 can be changed as follows:
536 Perl 5.6 added support for Unicode characters with code points > 255,
537 and Perl 5.8 has full support for Unicode characters in hash keys.
538 Perl internally encodes strings with these characters using utf8, and
539 Storable serializes them as utf8. By default, if an older version of
540 Perl encounters a utf8 value it cannot represent, it will C<croak()>.
541 To change this behaviour so that Storable deserializes utf8 encoded
542 values as the string of bytes (effectively dropping the I<is_utf8> flag)
543 set C<$Storable::drop_utf8> to some C<TRUE> value. This is a form of
544 data loss, because with C<$drop_utf8> true, it becomes impossible to tell
545 whether the original data was the Unicode string, or a series of bytes
546 that happen to be valid utf8.
548 =item restricted hashes
550 Perl 5.8 adds support for restricted hashes, which have keys
551 restricted to a given set, and can have values locked to be read only.
552 By default, when Storable encounters a restricted hash on a perl
553 that doesn't support them, it will deserialize it as a normal hash,
554 silently discarding any placeholder keys and leaving the keys and
555 all values unlocked. To make Storable C<croak()> instead, set
556 C<$Storable::downgrade_restricted> to a C<FALSE> value. To restore
557 the default set it back to some C<TRUE> value.
559 =item files from future versions of Storable
561 Earlier versions of Storable would immediately croak if they encountered
562 a file with a higher internal version number than the reading Storable
563 knew about. Internal version numbers are increased each time new data
564 types (such as restricted hashes) are added to the vocabulary of the file
565 format. This meant that a newer Storable module had no way of writing a
566 file readable by an older Storable, even if the writer didn't store newer
569 This version of Storable will defer croaking until it encounters a data
570 type in the file that it does not recognize. This means that it will
571 continue to read files generated by newer Storable modules which are careful
572 in what they write out, making it easier to upgrade Storable modules in a
575 The old behaviour of immediate croaking can be re-instated by setting
576 C<$Storable::accept_future_minor> to some C<FALSE> value.
580 All these variables have no effect on a newer Perl which supports the
583 =head1 ERROR REPORTING
585 Storable uses the "exception" paradigm, in that it does not try to workaround
586 failures: if something bad happens, an exception is generated from the
587 caller's perspective (see L<Carp> and C<croak()>). Use eval {} to trap
590 When Storable croaks, it tries to report the error via the C<logcroak()>
591 routine from the C<Log::Agent> package, if it is available.
593 Normal errors are reported by having store() or retrieve() return C<undef>.
594 Such errors are usually I/O errors (or truncated stream errors at retrieval).
600 Any class may define hooks that will be called during the serialization
601 and deserialization process on objects that are instances of that class.
602 Those hooks can redefine the way serialization is performed (and therefore,
603 how the symmetrical deserialization should be conducted).
605 Since we said earlier:
607 dclone(.) = thaw(freeze(.))
609 everything we say about hooks should also hold for deep cloning. However,
610 hooks get to know whether the operation is a mere serialization, or a cloning.
612 Therefore, when serializing hooks are involved,
614 dclone(.) <> thaw(freeze(.))
616 Well, you could keep them in sync, but there's no guarantee it will always
617 hold on classes somebody else wrote. Besides, there is little to gain in
618 doing so: a serializing hook could keep only one attribute of an object,
619 which is probably not what should happen during a deep cloning of that
622 Here is the hooking interface:
626 =item C<STORABLE_freeze> I<obj>, I<cloning>
628 The serializing hook, called on the object during serialization. It can be
629 inherited, or defined in the class itself, like any other method.
631 Arguments: I<obj> is the object to serialize, I<cloning> is a flag indicating
632 whether we're in a dclone() or a regular serialization via store() or freeze().
634 Returned value: A LIST C<($serialized, $ref1, $ref2, ...)> where $serialized
635 is the serialized form to be used, and the optional $ref1, $ref2, etc... are
636 extra references that you wish to let the Storable engine serialize.
638 At deserialization time, you will be given back the same LIST, but all the
639 extra references will be pointing into the deserialized structure.
641 The B<first time> the hook is hit in a serialization flow, you may have it
642 return an empty list. That will signal the Storable engine to further
643 discard that hook for this class and to therefore revert to the default
644 serialization of the underlying Perl data. The hook will again be normally
645 processed in the next serialization.
647 Unless you know better, serializing hook should always say:
649 sub STORABLE_freeze {
650 my ($self, $cloning) = @_;
651 return if $cloning; # Regular default serialization
655 in order to keep reasonable dclone() semantics.
657 =item C<STORABLE_thaw> I<obj>, I<cloning>, I<serialized>, ...
659 The deserializing hook called on the object during deserialization.
660 But wait: if we're deserializing, there's no object yet... right?
662 Wrong: the Storable engine creates an empty one for you. If you know Eiffel,
663 you can view C<STORABLE_thaw> as an alternate creation routine.
665 This means the hook can be inherited like any other method, and that
666 I<obj> is your blessed reference for this particular instance.
668 The other arguments should look familiar if you know C<STORABLE_freeze>:
669 I<cloning> is true when we're part of a deep clone operation, I<serialized>
670 is the serialized string you returned to the engine in C<STORABLE_freeze>,
671 and there may be an optional list of references, in the same order you gave
672 them at serialization time, pointing to the deserialized objects (which
673 have been processed courtesy of the Storable engine).
675 When the Storable engine does not find any C<STORABLE_thaw> hook routine,
676 it tries to load the class by requiring the package dynamically (using
677 the blessed package name), and then re-attempts the lookup. If at that
678 time the hook cannot be located, the engine croaks. Note that this mechanism
679 will fail if you define several classes in the same file, but L<perlmod>
682 It is up to you to use this information to populate I<obj> the way you want.
684 Returned value: none.
690 Predicates are not exportable. They must be called by explicitly prefixing
691 them with the Storable package name.
695 =item C<Storable::last_op_in_netorder>
697 The C<Storable::last_op_in_netorder()> predicate will tell you whether
698 network order was used in the last store or retrieve operation. If you
699 don't know how to use this, just forget about it.
701 =item C<Storable::is_storing>
703 Returns true if within a store operation (via STORABLE_freeze hook).
705 =item C<Storable::is_retrieving>
707 Returns true if within a retrieve operation (via STORABLE_thaw hook).
713 With hooks comes the ability to recurse back to the Storable engine.
714 Indeed, hooks are regular Perl code, and Storable is convenient when
715 it comes to serializing and deserializing things, so why not use it
716 to handle the serialization string?
718 There are a few things you need to know, however:
724 You can create endless loops if the things you serialize via freeze()
725 (for instance) point back to the object we're trying to serialize in
730 Shared references among objects will not stay shared: if we're serializing
731 the list of object [A, C] where both object A and C refer to the SAME object
732 B, and if there is a serializing hook in A that says freeze(B), then when
733 deserializing, we'll get [A', C'] where A' refers to B', but C' refers to D,
734 a deep clone of B'. The topology was not preserved.
738 That's why C<STORABLE_freeze> lets you provide a list of references
739 to serialize. The engine guarantees that those will be serialized in the
740 same context as the other objects, and therefore that shared objects will
743 In the above [A, C] example, the C<STORABLE_freeze> hook could return:
745 ("something", $self->{B})
747 and the B part would be serialized by the engine. In C<STORABLE_thaw>, you
748 would get back the reference to the B' object, deserialized for you.
750 Therefore, recursion should normally be avoided, but is nonetheless supported.
754 There is a Clone module available on CPAN which implements deep cloning
755 natively, i.e. without freezing to memory and thawing the result. It is
756 aimed to replace Storable's dclone() some day. However, it does not currently
757 support Storable hooks to redefine the way deep cloning is performed.
759 =head1 Storable magic
761 Yes, there's a lot of that :-) But more precisely, in UNIX systems
762 there's a utility called C<file>, which recognizes data files based on
763 their contents (usually their first few bytes). For this to work,
764 a certain file called F<magic> needs to taught about the I<signature>
765 of the data. Where that configuration file lives depends on the UNIX
766 flavour; often it's something like F</usr/share/misc/magic> or
767 F</etc/magic>. Your system administrator needs to do the updating of
768 the F<magic> file. The necessary signature information is output to
769 STDOUT by invoking Storable::show_file_magic(). Note that the GNU
770 implementation of the C<file> utility, version 3.38 or later,
771 is expected to contain support for recognising Storable files
772 out-of-the-box, in addition to other kinds of Perl files.
776 Here are some code samples showing a possible usage of Storable:
778 use Storable qw(store retrieve freeze thaw dclone);
780 %color = ('Blue' => 0.1, 'Red' => 0.8, 'Black' => 0, 'White' => 1);
782 store(\%color, '/tmp/colors') or die "Can't store %a in /tmp/colors!\n";
784 $colref = retrieve('/tmp/colors');
785 die "Unable to retrieve from /tmp/colors!\n" unless defined $colref;
786 printf "Blue is still %lf\n", $colref->{'Blue'};
788 $colref2 = dclone(\%color);
790 $str = freeze(\%color);
791 printf "Serialization of %%color is %d bytes long.\n", length($str);
792 $colref3 = thaw($str);
794 which prints (on my machine):
796 Blue is still 0.100000
797 Serialization of %color is 102 bytes long.
799 Serialization of CODE references and deserialization in a safe
802 use Storable qw(freeze thaw);
806 # permitting the "require" opcode is necessary when using "use strict"
807 $safe->permit(qw(:default require));
808 local $Storable::Deparse = 1;
809 local $Storable::Eval = sub { $safe->reval($_[0]) };
810 my $serialized = freeze(sub { print "42\n" });
811 my $code = thaw($serialized);
812 $code->(); # prints 42
816 If you're using references as keys within your hash tables, you're bound
817 to be disappointed when retrieving your data. Indeed, Perl stringifies
818 references used as hash table keys. If you later wish to access the
819 items via another reference stringification (i.e. using the same
820 reference that was used for the key originally to record the value into
821 the hash table), it will work because both references stringify to the
824 It won't work across a sequence of C<store> and C<retrieve> operations,
825 however, because the addresses in the retrieved objects, which are
826 part of the stringified references, will probably differ from the
827 original addresses. The topology of your structure is preserved,
828 but not hidden semantics like those.
830 On platforms where it matters, be sure to call C<binmode()> on the
831 descriptors that you pass to Storable functions.
833 Storing data canonically that contains large hashes can be
834 significantly slower than storing the same data normally, as
835 temporary arrays to hold the keys for each hash have to be allocated,
836 populated, sorted and freed. Some tests have shown a halving of the
837 speed of storing -- the exact penalty will depend on the complexity of
838 your data. There is no slowdown on retrieval.
842 You can't store GLOB, CODE, FORMLINE, etc.... If you can define
843 semantics for those operations, feel free to enhance Storable so that
844 it can deal with them.
846 The store functions will C<croak> if they run into such references
847 unless you set C<$Storable::forgive_me> to some C<TRUE> value. In that
848 case, the fatal message is turned in a warning and some
849 meaningless string is stored instead.
851 Setting C<$Storable::canonical> may not yield frozen strings that
852 compare equal due to possible stringification of numbers. When the
853 string version of a scalar exists, it is the form stored; therefore,
854 if you happen to use your numbers as strings between two freezing
855 operations on the same data structures, you will get different
858 When storing doubles in network order, their value is stored as text.
859 However, you should also not expect non-numeric floating-point values
860 such as infinity and "not a number" to pass successfully through a
861 nstore()/retrieve() pair.
863 As Storable neither knows nor cares about character sets (although it
864 does know that characters may be more than eight bits wide), any difference
865 in the interpretation of character codes between a host and a target
866 system is your problem. In particular, if host and target use different
867 code points to represent the characters used in the text representation
868 of floating-point numbers, you will not be able be able to exchange
869 floating-point data, even with nstore().
871 C<Storable::drop_utf8> is a blunt tool. There is no facility either to
872 return B<all> strings as utf8 sequences, or to attempt to convert utf8
873 data back to 8 bit and C<croak()> if the conversion fails.
875 Prior to Storable 2.01, no distinction was made between signed and
876 unsigned integers on storing. By default Storable prefers to store a
877 scalars string representation (if it has one) so this would only cause
878 problems when storing large unsigned integers that had never been coverted
879 to string or floating point. In other words values that had been generated
880 by integer operations such as logic ops and then not used in any string or
881 arithmetic context before storing.
883 =head2 64 bit data in perl 5.6.0 and 5.6.1
885 This section only applies to you if you have existing data written out
886 by Storable 2.02 or earlier on perl 5.6.0 or 5.6.1 on Unix or Linux which
887 has been configured with 64 bit integer support (not the default)
888 If you got a precompiled perl, rather than running Configure to build
889 your own perl from source, then it almost certainly does not affect you,
890 and you can stop reading now (unless you're curious). If you're using perl
891 on Windows it does not affect you.
893 Storable writes a file header which contains the sizes of various C
894 language types for the C compiler that built Storable (when not writing in
895 network order), and will refuse to load files written by a Storable not
896 on the same (or compatible) architecture. This check and a check on
897 machine byteorder is needed because the size of various fields in the file
898 are given by the sizes of the C language types, and so files written on
899 different architectures are incompatible. This is done for increased speed.
900 (When writing in network order, all fields are written out as standard
901 lengths, which allows full interworking, but takes longer to read and write)
903 Perl 5.6.x introduced the ability to optional configure the perl interpreter
904 to use C's C<long long> type to allow scalars to store 64 bit integers on 32
905 bit systems. However, due to the way the Perl configuration system
906 generated the C configuration files on non-Windows platforms, and the way
907 Storable generates its header, nothing in the Storable file header reflected
908 whether the perl writing was using 32 or 64 bit integers, despite the fact
909 that Storable was storing some data differently in the file. Hence Storable
910 running on perl with 64 bit integers will read the header from a file
911 written by a 32 bit perl, not realise that the data is actually in a subtly
912 incompatible format, and then go horribly wrong (possibly crashing) if it
913 encountered a stored integer. This is a design failure.
915 Storable has now been changed to write out and read in a file header with
916 information about the size of integers. It's impossible to detect whether
917 an old file being read in was written with 32 or 64 bit integers (they have
918 the same header) so it's impossible to automatically switch to a correct
919 backwards compatibility mode. Hence this Storable defaults to the new,
922 What this means is that if you have data written by Storable 1.x running
923 on perl 5.6.0 or 5.6.1 configured with 64 bit integers on Unix or Linux
924 then by default this Storable will refuse to read it, giving the error
925 I<Byte order is not compatible>. If you have such data then you you
926 should set C<$Storable::interwork_56_64bit> to a true value to make this
927 Storable read and write files with the old header. You should also
928 migrate your data, or any older perl you are communicating with, to this
929 current version of Storable.
931 If you don't have data written with specific configuration of perl described
932 above, then you do not and should not do anything. Don't set the flag -
933 not only will Storable on an identically configured perl refuse to load them,
934 but Storable a differently configured perl will load them believing them
935 to be correct for it, and then may well fail or crash part way through
940 Thank you to (in chronological order):
942 Jarkko Hietaniemi <jhi@iki.fi>
943 Ulrich Pfeifer <pfeifer@charly.informatik.uni-dortmund.de>
944 Benjamin A. Holzman <bah@ecnvantage.com>
945 Andrew Ford <A.Ford@ford-mason.co.uk>
946 Gisle Aas <gisle@aas.no>
947 Jeff Gresham <gresham_jeffrey@jpmorgan.com>
948 Murray Nesbitt <murray@activestate.com>
949 Marc Lehmann <pcg@opengroup.org>
950 Justin Banks <justinb@wamnet.com>
951 Jarkko Hietaniemi <jhi@iki.fi> (AGAIN, as perl 5.7.0 Pumpkin!)
952 Salvador Ortiz Garcia <sog@msg.com.mx>
953 Dominic Dunlop <domo@computer.org>
954 Erik Haugan <erik@solbors.no>
956 for their bug reports, suggestions and contributions.
958 Benjamin Holzman contributed the tied variable support, Andrew Ford
959 contributed the canonical order for hashes, and Gisle Aas fixed
960 a few misunderstandings of mine regarding the perl internals,
961 and optimized the emission of "tags" in the output streams by
962 simply counting the objects instead of tagging them (leading to
963 a binary incompatibility for the Storable image starting at version
964 0.6--older images are, of course, still properly understood).
965 Murray Nesbitt made Storable thread-safe. Marc Lehmann added overloading
966 and references to tied items support.
970 Storable was written by Raphael Manfredi F<E<lt>Raphael_Manfredi@pobox.comE<gt>>
971 Maintenance is now done by the perl5-porters F<E<lt>perl5-porters@perl.orgE<gt>>
973 Please e-mail us with problems, bug fixes, comments and complaints,
974 although if you have complements you should send them to Raphael.
975 Please don't e-mail Raphael with problems, as he no longer works on
976 Storable, and your message will be delayed while he forwards it to us.