1FFI::Platypus::Type(3)User Contributed Perl DocumentationFFI::Platypus::Type(3)
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NAME

6       FFI::Platypus::Type - Defining types for FFI::Platypus
7

VERSION

9       version 1.56
10

SYNOPSIS

12       OO Interface:
13
14        use FFI::Platypus 1.00;
15        my $ffi = FFI::Platypus->new( api => 1 );
16        $ffi->type('int' => 'my_int');
17

DESCRIPTION

19       Note: This document assumes that you are using "api => 1", which you
20       should be using for all new code.
21
22       This document describes how to define types using FFI::Platypus.  Types
23       may be "defined" ahead of time, or simply used when defining or
24       attaching functions.
25
26        # Example of defining types
27        use FFI::Platypus 1.00;
28        my $ffi = FFI::Platypus->new( api => 1 );
29        $ffi->type('int');
30        $ffi->type('string');
31
32        # Example of simply using types in function declaration or attachment
33        my $f = $ffi->function(puts => ['string'] => 'int');
34        $ffi->attach(puts => ['string'] => 'int');
35
36       Unless you are using aliases the FFI::Platypus#type method is not
37       necessary, but they will throw an exception if the type is incorrectly
38       specified or not supported, which may be helpful for determining if the
39       types are available or not.
40
41       Note: This document sometimes uses the term "C Function" as short hand
42       for function implemented in a compiled language.  Unless the term is
43       referring literally to a C function example code, you can assume that
44       it should also work with another compiled language.
45
46   meta information about types
47       You can get the size of a type using the FFI::Platypus#sizeof method.
48
49        my $intsize = $ffi->sizeof('int');           # usually 4
50        my $intarraysize = $ffi->sizeof('int[64]');  # usually 256
51
52   converting types
53       Sometimes it is necessary to convert types.  In particular various
54       pointer types often need to be converted for consumption in Perl.  For
55       this purpose the FFI::Platypus#cast method is provided.  It needs to be
56       used with care though, because not all type combinations are supported.
57       Here are some useful ones:
58
59        my $address = $ffi->cast('string' => 'opaque', $string);
60
61       This converts a Perl string to a pointer address that can be used by
62       functions that take an "opaque" type.  Be carefully though that the
63       Perl string is not resized or free'd while in use from C code.
64
65        my $string  = $ffi->cast('opaque' => 'string', $pointer);
66
67       This does the opposite, converting a null terminated string (the type
68       of strings used by C) into a Perl string.  In this case the string is
69       copied, so the other language is free to deallocate or otherwise
70       manipulate the string after the conversion without adversely affecting
71       the Perl.
72
73   aliases
74       Some times using alternate names is useful for documenting the purpose
75       of an argument or return type.  For this "aliases" can be helpful.  The
76       second argument to the FFI::Platypus#type method can be used to define
77       a type alias that can later be used by function declaration and
78       attachment.
79
80        use FFI::Platypus 1.00;
81        my $ffi = FFI::Platypus->new( api => 1 );
82        $ffi->type('int'    => 'myint');
83        $ffi->type('string' => 'mystring');
84        my $f = $ffi->function( puts => ['mystring'] => 'myint' );
85        $ffi->attach( puts => ['mystring'] => 'myint' );
86
87       Aliases are contained without the FFI::Platypus object, so feel free to
88       define your own crazy types without stepping on the toes of other CPAN
89       developers using Platypus.
90
91       One useful application of an alias is when you know types are different
92       on two different platforms:
93
94        if($^O eq 'MSWin32')
95        {
96          $type->type('sint16' => 'foo_t');
97        } elsif($^O eq 'linux')
98        {
99          $type->type('sint32' => 'foo_t');
100        }
101
102        # function foo takes 16 bit signed integer on Windows
103        # and a 32 bit signed integer on Linux.
104        $ffi->attach( foo => [ 'foo_t' ] => 'void' );
105

TYPE CATEGORIES

107   Native types
108       So called native types are the types that the CPU understands that can
109       be passed on the argument stack or returned by a function.  It does not
110       include more complicated types like arrays or structs, which can be
111       passed via pointers (see the opaque type below).  Generally native
112       types include void, integers, floats and pointers.
113
114       the void type
115
116       This can be used as a return value to indicate a function does not
117       return a value (or if you want the return value to be ignored).
118
119        $ffi->type( foo => [] => 'void' );
120
121       Newer versions of Platypus also allow you to omit the return type and
122       "void" is assumed.
123
124        $ffi->type( foo => [] );
125
126       It doesn't really make sense to use "void" in any other context.
127       However, because of historical reasons involving older versions of
128       Perl.
129
130       It doesn't really make sense for "void" to be passed in as an argument.
131       However, because C functions that take no arguments frequently are
132       specified as taking "void" as this was required by older C compilers,
133       as a special case you can specify a function's arguments as taking a
134       single "void" to mean it takes no arguments.
135
136        # C: void foo(void);
137        $ffi->type( foo => ['void'] );
138        # same (but probably better)
139        $ffi->type( foo => [] );
140
141       integer types
142
143       The following native integer types are always available (parentheticals
144       indicates the usual corresponding C type):
145
146       sint8
147           Signed 8 bit byte ("signed char", "int8_t").
148
149       uint8
150           Unsigned 8 bit byte ("unsigned char", "uint8_t").
151
152       sint16
153           Signed 16 bit integer ("short", "int16_t")
154
155       uint16
156           Unsigned 16 bit integer ("unsigned short", "uint16_t")
157
158       sint32
159           Signed 32 bit integer ("int", "int32_t")
160
161       uint32
162           Unsigned 32 bit integer ("unsigned int", "uint32_t")
163
164       sint64
165           Signed 64 bit integer ("long long", "int64_t")
166
167       uint64
168           Unsigned 64 bit integer ("unsigned long long", "uint64_t")
169
170       You may also use "uchar", "ushort", "uint" and "ulong" as short names
171       for "unsigned char", "unsigned short", "unsigned int" and "unsigned
172       long".
173
174       These integer types are also available, but there actual size and sign
175       may depend on the platform.
176
177       char
178           Somewhat confusingly, "char" is an integer type!  This is really an
179           alias for either "sint8_t" or "uint8_t" depending on your platform.
180           If you want to pass a character (not integer) in to a C function
181           that takes a character you want to use the perl ord function.  Here
182           is an example that uses the standard libc "isalpha", "isdigit" type
183           functions:
184
185            use FFI::Platypus 1.00;
186
187            my $ffi = FFI::Platypus->new( api => 1 );
188            $ffi->lib(undef);
189            $ffi->type('int' => 'character');
190
191            my @list = qw(
192              alnum alpha ascii blank cntrl digit lower print punct
193              space upper xdigit
194            );
195
196            $ffi->attach("is$_" => ['character'] => 'int') for @list;
197
198            my $char = shift(@ARGV) || 'a';
199
200            no strict 'refs';
201            printf "'%s' is %s %s\n", $char, $_, &{'is'.$_}(ord $char) for @list;
202
203       size_t
204           This is usually an "unsigned long", but it is up to the compiler to
205           decide.  The "malloc" function is defined in terms of "size_t":
206
207            $ffi->attach( malloc => ['size_t'] => 'opaque';
208
209           (Note that you can get "malloc" from FFI::Platypus::Memory).
210
211       long, unsigned long
212           On 64 bit systems, this is usually a 64 bit integer.  On 32 bit
213           systems this is frequently a 32 bit integer (and "long long" or
214           "unsigned long long" are for 64 bit).
215
216       There are a number of other types that may or may not be available if
217       they are detected when FFI::Platypus is installed.  This includes
218       things like "wchar_t", "off_t", "wint_t". You can use this script to
219       list all the integer types that FFI::Platypus knows about, plus how
220       they are implemented.
221
222        use FFI::Platypus 1.00;
223
224        my $ffi = FFI::Platypus->new( api => 1 );
225
226        foreach my $type_name (sort $ffi->types)
227        {
228          my $meta = $ffi->type_meta($type_name);
229          next unless defined $meta->{element_type} && $meta->{element_type} eq 'int';
230          printf "%20s %s\n", $type_name, $meta->{ffi_type};
231        }
232
233       If you need a common system type that is not provided, please open a
234       ticket in the Platypus project's GitHub issue tracker.  Be sure to
235       include the usual header file the type can be found in.
236
237       Enum types
238
239       C provides enumerated types, which are typically implemented as integer
240       types.
241
242        enum {
243          BAR = 1,
244          BAZ = 2
245        } foo_t;
246
247        void f(enum foo_t foo);
248
249       Platypus provides "enum" and "senum" types for the integer types used
250       to represent enum and signed enum types respectively.
251
252        use constant BAR => 1;
253        use constant BAZ => 2;
254        $ffi->attach( f => [ 'enum' ] => 'void' );
255        f(BAR);
256        f(BAZ);
257
258       When do you use "senum"?  Anytime the enum has negative values:
259
260        enum {
261          BAR = -1;
262          BAZ = 2;
263        } foo_t;
264
265        void f(enum foo_t foo);
266
267       Perl:
268
269        use constant BAR => -1;
270        use constant BAZ => 2;
271        $ffi->attach( f => [ 'senum' ] => 'void' );
272        f(BAR);
273        f(BAZ);
274
275       Dealing with enumerated values with FFI can be tricky because these are
276       usually defined in C header files and cannot be found in dynamic
277       libraries.  For trivial usage you can do as illustrated above, simply
278       define your own Perl constants.  For more complicated usage, or where
279       the values might vary from platform to platform you may want to
280       consider the new Platypus bundle interface to define Perl constants
281       (essentially the same as an enumerated value) from C space.  This is
282       more reliable, but does require a compiler at install time.  See
283       FFI::Platypus::Constant for details.
284
285       The main FAQ ("FAQ" in FFI::Platypus) also has a discussion on dealing
286       with constants and enumerated types.
287
288       There is also a type plugin (FFI::Platypus::Type::Enum) that can be
289       helpful in writing interfaces that use enums.
290
291       Boolean types
292
293       At install time Platypus attempts to detect the correct type for "bool"
294       for your platform, and you can use that.  "bool" is really an integer
295       type, but the type used varies from platform to platform.
296
297       C header:
298
299        #include <stdbool.h>
300        bool foo();
301
302       Platypus
303
304        $ffi->attach( foo => [] => 'bool' );
305
306       If you get an exception when trying to use this type it means you
307       either have a very old version of Platypus, or for some reason it was
308       unable to detect the correct type at install time.  Please open a
309       ticket if that is the case.
310
311       floating point types
312
313       The following native floating point types are always available
314       (parentheticals indicates the usual corresponding C type):
315
316       float
317           Single precision floating point (float)
318
319       double
320           Double precision floating point (double)
321
322       longdouble
323           Floating point that may be larger than "double" (longdouble).  This
324           type is only available if supported by the C compiler used to build
325           FFI::Platypus.  There may be a performance penalty for using this
326           type, even if your Perl uses long doubles internally for its number
327           value (NV) type, because of the way FFI::Platypus interacts with
328           "libffi".
329
330           As an argument type either regular number values (NV) or instances
331           of Math::LongDouble are accepted.  When used as a return type,
332           Math::LongDouble will be used, if you have that module installed.
333           Otherwise the return type will be downgraded to whatever your
334           Perl's number value (NV) is.
335
336       complex_float
337           Complex single precision floating point (float complex)
338
339       complex_double
340           Complex double precision floating point (double complex)
341
342           "complex_float" and "complex_double" are only available if
343           supported by your C compiler and by libffi.  Complex numbers are
344           only supported in very recent versions of libffi, and as of this
345           writing the latest production version doesn't work on x86_64.  It
346           does seem to work with the latest production version of libffi on
347           32 bit Intel (x86), and with the latest libffi version in git on
348           x86_64.
349
350       opaque pointers
351
352       Opaque pointers are simply a pointer to a region of memory that you do
353       not manage, and do not know or care about its structure. It is like a
354       "void *" in C.  These types are represented in Perl space as integers
355       and get converted to and from pointers by FFI::Platypus.  You may use
356       "pointer" as an alias for "opaque", although this is discouraged.  (The
357       Platypus documentation uses the convention of using "pointer" to refer
358       to pointers to known types (see below) and "opaque" as short hand for
359       opaque pointer).
360
361       As an example, libarchive defines "struct archive" type in its header
362       files, but does not define its content.  Internally it is defined as a
363       "struct" type, but the caller does not see this.  It is therefore
364       opaque to its caller.  There are "archive_read_new" and
365       "archive_write_new" functions to create a new instance of this opaque
366       object and "archive_read_free" and "archive_write_free" to destroy this
367       objects when you are done.
368
369       C header:
370
371        struct archive;
372        struct archive *archive_read_new(void);
373        struct archive *archive_write_new(void);
374        int archive_free(struct archive *);
375        int archive_write_free(struct archive *);
376
377       Perl code:
378
379        $lib->find_lib( lib => 'archive' );
380        $ffi->attach(archive_read_new   => []         => 'opaque');
381        $ffi->attach(archive_write_new  => []         => 'opaque');
382        $ffi->attach(archive_read_free  => ['opaque'] => 'int');
383        $ffi->attach(archive_write_free => ['opaque'] => 'int');
384
385       It is often useful to alias an "opaque" type like this so that you know
386       what the object represents:
387
388        $lib->find_lib( lib => 'archive' );
389        $ffi->type('opaque' => 'archive');
390        $ffi->attach(archive_read_new   => [] => 'archive');
391        $ffi->attach(archive_read_free  => ['archive'] => 'int');
392        ...
393
394       As a special case, when you pass "undef" into a function that takes an
395       opaque type it will be translated into "NULL" for C.  When a C function
396       returns a NULL pointer, it will be translated back to "undef".
397
398       For functions that take a pointer to a void pointer (that is a "void
399       **"), you can use a pointer to an opaque type.  Consider the C code:
400
401        struct archive_entry;
402        int archive_read_next_header(struct archive *, struvct archive_entry **);
403
404       Once again the internals of "archive_entry" are not provided.  Perl
405       code:
406
407        $ffi->type('opaque' => 'archive_entry');
408        $ffi->attach(archive_read_next_header => [ 'archive', 'archive_entry*' ] => 'int');
409
410       Now we can call this function
411
412        my $archive = archive_read_new();
413        ...  # additional prep for $active is required
414        while(1) {
415          my $entry;
416          archive_read_next_header($archive, \$entry);
417          last unless defined $entry;
418          # can now use $entry for other archive_entry_ methods.
419        }
420
421       The way "archive_read_next_header" works, it will return a pointer to
422       the next "archive_entry" object until it gets to the end, when it will
423       return a pointer to "NULL" which will be represented in Perl by a
424       "undef".
425
426       There are a number of useful utility functions for dealing with opaque
427       types in the FFI::Platypus::Memory module.
428
429   Objects
430       Object types are thin wrappers around two native types: integer and
431       "opaque" types.  They are just blessed references around either of
432       those two types so that methods can be defined on them, but when they
433       get passed to a Platypus xsub they are converted into the native
434       integer or "opaque" types.  This type is most useful when a API
435       provides an OO style interface with an integer or "opaque" value acting
436       as an instance of a class.  There are two detailed examples in the main
437       Platypus documentation using libarchive and unix open:
438
439       "libarchive" in FFI::Platypus
440       "unix open" in FFI::Platypus
441
442   Strings
443       From the CPU's perspective, strings are just pointers.  From Perl and
444       C's perspective, those pointers point to a series of characters.  For C
445       they are null terminates ("\0").  FFI::Platypus handles the details
446       where they differ.  Basically when you see "char *" or "const char *"
447       used in a C header file you can expect to be able to use the "string"
448       type.
449
450        $ffi->attach( puts => [ 'string' ] => 'int' );
451
452       The pointer passed into C (or other language) is to the content of the
453       actual scalar, which means it can modify the content of a scalar.
454
455       NOTE: When used as a return type, the string is copied into a new
456       scalar rather than using the original address.  This is due to the
457       ownership model of scalars in Perl, but it is also most of the time
458       what you want.
459
460       This can be problematic when a function returns a string that the
461       callee is expected to free.  Consider the functions:
462
463        char *
464        get_string()
465        {
466          char *buffer;
467          buffer = malloc(20);
468          strcpy(buffer, "Perl");
469        }
470
471        void
472        free_string(char *buffer)
473        {
474          free(buffer);
475        }
476
477       This API returns a string that you are expected to free when you are
478       done with it.  (At least they have provided an API for freeing the
479       string instead of expecting you to call libc free)!  A simple binding
480       to get the string would be:
481
482        $ffi->attach( get_string => [] => 'string' );  # memory leak
483        my $str = get_string();
484
485       Which will work to a point, but the memory allocated by get_string will
486       leak.  Instead you need to get the opaque pointer, cast it to a string
487       and then free it.
488
489        $ffi->attach( get_string => [] => 'opaque' );
490        $ffi->attach( free_string => ['opaque'] => 'void' );
491        my $ptr = get_string();
492        my $str = $ffi->cast( 'opaque' => 'string', $ptr );  # copies the string
493        free_string($ptr);
494
495       If you are doing this sort of thing a lot, it can be worth adding a
496       custom type:
497
498        $ffi->attach( free_string => ['opaque'] => 'void' );
499        $ffi->custom_type( 'my_string' => {
500          native_type => 'opaque',
501          native_to_perl => sub {
502            my($ptr) = @_;
503            my $str = $ffi->cast( 'opaque' => 'string', $ptr ); # copies the string
504            free_string($ptr);
505            $str;
506          }
507        });
508
509        $ffi->attach( get_string => [] => 'my_string' );
510        my $str = get_string();
511
512       Since version 0.62, pointers and arrays to strings are supported as a
513       first class type.  Prior to that FFI::Platypus::Type::StringArray and
514       FFI::Platypus::Type::StringPointer could be used, though their use in
515       new code is discouraged.
516
517        $ffi->attach( foo => ['string[]'] => 'void' );
518        foo( [ 'array', 'of', 'strings' ] );
519
520        $ffi->attach( bar => ['string*'] => 'void' );
521        my $string = 'baz';
522        bar( \$string );  # $string may be modified.
523
524       Strings are not allowed as return types from closure.  This, again is
525       due to the ownership model of scalars in Perl.  (There is no way for
526       Perl to know when calling language is done with the memory allocated to
527       the string).  Consider the API:
528
529        typedef const char *(*get_message_t)(void);
530
531        void
532        print_message(get_message_t get_message)
533        {
534          const char *str;
535          str = get_message();
536          printf("message = %s\n", str);
537        }
538
539       It feels like this should be able to work:
540
541        $ffi->type('()->string' => 'get_message_t'); # not ok
542        $ffi->attach( print_message => ['get_message_t'] => 'void' );
543        my $get_message = $ffi->closure(sub {
544          return "my message";
545        });
546        print_message($get_message);
547
548       If the type declaration for "get_message_t" were legal, then this
549       script would likely segfault or in the very least corrupt memory.  The
550       problem is that once "my message" is returned from the closure Perl
551       doesn't have a reference to it anymore and will free it.  To do this
552       safely, you have to keep a reference to the scalar around and return an
553       opaque pointer to the string using a cast.
554
555        $ffi->type('()->opaque' => 'get_message_t');
556        $ffi->attach( print_message => ['get_message_t'] => 'void' );
557        my $get_message => $ffi->closure(sub {
558          our $message = "my message";  # needs to be our so that it doesn't
559                                        # get free'd
560          my $ptr = $ffi->cast('string' => 'opaque', $message);
561          return $ptr;
562        });
563        print_message($get_message);
564
565       Another type of string that you may run into with some APIs is the so
566       called "wide" string.  In your C code if you see "wchar_t*" or "const
567       wchar_t*" or if in Win32 API code you see "LPWSTR" or "LPCWSTR".  Most
568       commonly you will see these types when working with the Win32 API, but
569       you may see them in Unix as well.  These types are intended for dealing
570       with Unicode, but they do not use the same UTF-8 format used by Perl
571       internally, so they need to be converted.  You can do this manually by
572       allocating the memory and using the Encode module, but the easier way
573       is to use either FFI::Platypus::Type::WideString or
574       FFI::Platypus::Lang::Win32, which handle the memory allocation and
575       conversion for you.
576
577   Pointer / References
578       In C you can pass a pointer to a variable to a function in order
579       accomplish the task of pass by reference.  In Perl the same task is
580       accomplished by passing a reference (although you can also modify the
581       argument stack thus Perl supports proper pass by reference as well).
582
583       With FFI::Platypus you can define a pointer to any native, string or
584       record type.  You cannot (at least not yet) define a pointer to a
585       pointer or a pointer to an array or any other type not otherwise
586       supported.  When passing in a pointer to something you must make sure
587       to pass in a reference to a scalar, or "undef" ("undef" will be
588       translated int "NULL").
589
590       If the C code makes a change to the value pointed to by the pointer,
591       the scalar will be updated before returning to Perl space.  Example,
592       with C code.
593
594        /* foo.c */
595        void increment_int(int *value)
596        {
597          if(value != NULL)
598            (*value)++;
599          else
600            fprintf(stderr, "NULL pointer!\n");
601        }
602
603        # foo.pl
604        use FFI::Platypus 1.00;
605        my $ffi = FFI::Platypus->new( api => 1 );
606        $ffi->lib('libfoo.so'); # change to reflect the dynamic lib
607                                # that contains foo.c
608        $ffi->type('int*' => 'int_p');
609        $ffi->attach(increment_int => ['int_p'] => 'void');
610        my $i = 0;
611        increment_int(\$i);   # $i == 1
612        increment_int(\$i);   # $i == 2
613        increment_int(\$i);   # $i == 3
614        increment_int(undef); # prints "NULL pointer!\n"
615
616       Older versions of Platypus did not support pointers to strings or
617       records.
618
619   Records
620       Records are structured data of a fixed length.  In C they are called
621       "struct"s.
622
623       The Platypus native way of working with structured data is via the
624       "record" type. There is also FFI::C which has some overlapping
625       functionality.  Briefly, FFI::C supports "union" and arrays of
626       structured types, but not passing structured data by-value, while the
627       "record" type doesn't support "union" or arrays of structured data, but
628       does support passing structured data by-value.  The remainder of this
629       section will discuss the native Platypus "record" type, but you should
630       remember that for some applications FFI::C might be more appropriate.
631
632       To declare a record type, use "record":
633
634        $ffi->type( 'record (42)' => 'my_record_of_size_42_bytes' );
635
636       The easiest way to mange records with Platypus is by using
637       FFI::Platypus::Record to define a record layout for a record class.
638       Here is a brief example:
639
640        package Unix::TimeStruct;
641
642        use FFI::Platypus 1.00;
643        use FFI::Platypus::Record;
644
645        record_layout_1(qw(
646            int    tm_sec
647            int    tm_min
648            int    tm_hour
649            int    tm_mday
650            int    tm_mon
651            int    tm_year
652            int    tm_wday
653            int    tm_yday
654            int    tm_isdst
655            long   tm_gmtoff
656            string tm_zone
657        ));
658
659        my $ffi = FFI::Platypus->new( api => 1 );
660        $ffi->lib(undef);
661        # define a record class Unix::TimeStruct and alias it to "tm"
662        $ffi->type("record(Unix::TimeStruct)*" => 'tm');
663
664        # attach the C localtime function as a constructor
665        $ffi->attach( localtime => ['time_t*'] => 'tm', sub {
666          my($inner, $class, $time) = @_;
667          $time = time unless defined $time;
668          $inner->(\$time);
669        });
670
671        package main;
672
673        # now we can actually use our Unix::TimeStruct class
674        my $time = Unix::TimeStruct->localtime;
675        printf "time is %d:%d:%d %s\n",
676          $time->tm_hour,
677          $time->tm_min,
678          $time->tm_sec,
679          $time->tm_zone;
680
681       For more detailed usage, see FFI::Platypus::Record.
682
683       Platypus does not manage the structure of a record (that is up to you),
684       it just keeps track of their size and makes sure that they are copied
685       correctly when used as a return type.  A record in Perl is just a
686       string of bytes stored as a scalar.  In addition to defining a record
687       layout for a record class, there are a number of tools you can use
688       manipulate records in Perl, two notable examples are pack and unpack
689       and Convert::Binary::C.
690
691       Here is an example with commentary that uses Convert::Binary::C to
692       extract the component time values from the C "localtime" function, and
693       then smushes them back together to get the original "time_t" (an
694       integer).
695
696        use Convert::Binary::C;
697        use FFI::Platypus 1.00;
698        use Data::Dumper qw( Dumper );
699
700        my $c = Convert::Binary::C->new;
701
702        # Alignment of zero (0) means use
703        # the alignment of your CPU
704        $c->configure( Alignment => 0 );
705
706        # parse the tm record structure so
707        # that Convert::Binary::C knows
708        # what to spit out and suck in
709        $c->parse(<<ENDC);
710        struct tm {
711          int tm_sec;
712          int tm_min;
713          int tm_hour;
714          int tm_mday;
715          int tm_mon;
716          int tm_year;
717          int tm_wday;
718          int tm_yday;
719          int tm_isdst;
720          long int tm_gmtoff;
721          const char *tm_zone;
722        };
723        ENDC
724
725        # get the size of tm so that we can give it
726        # to Platypus
727        my $tm_size = $c->sizeof("tm");
728
729        # create the Platypus instance and create the appropriate
730        # types and functions
731        my $ffi = FFI::Platypus->new( api => 1 );
732        $ffi->lib(undef);
733        $ffi->type("record($tm_size)*" => 'tm');
734        $ffi->attach( [ localtime => 'my_localtime' ] => ['time_t*'] => 'tm'     );
735        $ffi->attach( [ time      => 'my_time'      ] => ['tm']      => 'time_t' );
736
737        # ===============================================
738        # get the tm struct from the C localtime function
739        # note that we pass in a reference to the value that time
740        # returns because localtime takes a pointer to time_t
741        # for some reason.
742        my $time_hashref = $c->unpack( tm => my_localtime(\time) );
743
744        # tm_zone comes back from Convert::Binary::C as an opaque,
745        # cast it into a string.  We localize it to just this do
746        # block so that it will be a pointer when we pass it back
747        # to C land below.
748        do {
749          local $time_hashref->{tm_zone} = $ffi->cast(opaque => string => $time_hashref->{tm_zone});
750          print Dumper($time_hashref);
751        };
752
753        # ===============================================
754        # convert the tm struct back into an epoch value
755        my $time = my_time( $c->pack( tm => $time_hashref ) );
756
757        print "time      = $time\n";
758        print "perl time = ", time, "\n";
759
760       You can also link a record type to a class.  It will then be accepted
761       when blessed into that class as an argument passed into a C function,
762       and when it is returned from a C function it will be blessed into that
763       class.  Basically:
764
765        $ffi->type( 'record(My::Class)*' => 'my_class' );
766        $ffi->attach( my_function1 => [ 'my_class' ] => 'void' );
767        $ffi->attach( my_function2 => [ ] => 'my_class' );
768
769       The only thing that your class MUST provide is either a
770       "ffi_record_size" or "_ffi_record_size" class method that returns the
771       size of the record in bytes.
772
773       Here is a longer practical example, once again using the tm struct:
774
775        package Unix::TimeStruct;
776
777        use FFI::Platypus 1.00;
778        use FFI::TinyCC;
779        use FFI::TinyCC::Inline 'tcc_eval';
780
781        # store the source of the tm struct
782        # for repeated use later
783        my $tm_source = <<ENDTM;
784          struct tm {
785            int tm_sec;
786            int tm_min;
787            int tm_hour;
788            int tm_mday;
789            int tm_mon;
790            int tm_year;
791            int tm_wday;
792            int tm_yday;
793            int tm_isdst;
794            long int tm_gmtoff;
795            const char *tm_zone;
796          };
797        ENDTM
798
799        # calculate the size of the tm struct
800        # this time using Tiny CC
801        my $tm_size = tcc_eval qq{
802          $tm_source
803          int main()
804          {
805            return sizeof(struct tm);
806          }
807        };
808
809        # To use Unix::TimeStruct as a record class, we need to
810        # specify a size for the record, a function called
811        # either ffi_record_size or _ffi_record_size should
812        # return the size in bytes.  This function has to
813        # be defined before you try to define it as a type.
814        sub _ffi_record_size { $tm_size };
815
816        my $ffi = FFI::Platypus->new( api => 1 );
817        $ffi->lib(undef);
818        # define a record class Unix::TimeStruct and alias it
819        # to "tm"
820        $ffi->type("record(Unix::TimeStruct)*" => 'tm');
821
822        # attach the C localtime function as a constructor
823        $ffi->attach( [ localtime => '_new' ] => ['time_t*'] => 'tm' );
824
825        # the constructor needs to be wrapped in a Perl sub,
826        # because localtime is expecting the time_t (if provided)
827        # to come in as the first argument, not the second.
828        # We could also acomplish something similar using
829        # custom types.
830        sub new { _new(\($_[1] || time)) }
831
832        # for each attribute that we are interested in, create
833        # get and set accessors.  We just make accessors for
834        # hour, minute and second, but we could make them for
835        # all the fields if we needed.
836        foreach my $attr (qw( hour min sec ))
837        {
838          my $tcc = FFI::TinyCC->new;
839          $tcc->compile_string(qq{
840            $tm_source
841            int
842            get_$attr (struct tm *tm)
843            {
844              return tm->tm_$attr;
845            }
846            void
847            set_$attr (struct tm *tm, int value)
848            {
849              tm->tm_$attr = value;
850            }
851          });
852          $ffi->attach( [ $tcc->get_symbol("get_$attr") => "get_$attr" ] => [ 'tm' ] => 'int' );
853          $ffi->attach( [ $tcc->get_symbol("set_$attr") => "set_$attr" ] => [ 'tm' ] => 'int' );
854        }
855
856        package main;
857
858        # now we can actually use our Unix::TimeStruct class
859        my $time = Unix::TimeStruct->new;
860        printf "time is %d:%d:%d\n", $time->get_hour, $time->get_min, $time->get_sec;
861
862       Contrast a record type which is stored as a scalar string of bytes in
863       Perl to an opaque pointer which is stored as an integer in Perl.  Both
864       are treated as pointers in C functions.  The situations when you
865       usually want to use a record are when you know ahead of time what the
866       size of the object that you are working with and probably something
867       about its structure.  Because a function that returns a structure
868       copies the structure into a Perl data structure, you want to make sure
869       that it is okay to copy the record objects that you are dealing with if
870       any of your functions will be returning one of them.
871
872       Opaque pointers should be used when you do not know the size of the
873       object that you are using, or if the objects are created and free'd
874       through an API interface other than "malloc" and "free".
875
876       The examples in this section actually use pointers to records (note the
877       trailing star "*" in the declarations).  Most programming languages
878       allow you to pass or return a record as either pass-by-value or as a
879       pointer (pass-by-reference).
880
881       C code:
882
883        struct { int a; } foo_t;
884        void pass_by_value_example( struct foo_t foo );
885        void pass_by_reference_example( struct foo_t *foo );
886
887       Perl code:
888
889        {
890          package Foo;
891          use FFI::Platypus::Record;
892          record_layout_1( int => 'a' );
893        }
894        $ffi->type( 'Record(Foo)' => 'foo_t' );
895        $ffi->attach( pass_by_value_example => [ 'foo_t' ] => 'void' );
896        $ffi->attach( pass_by_reference_example => [ 'foo_t*' ] => 'void' );
897
898       As with strings, functions that return a pointer to a record are
899       actually copied.
900
901       C code:
902
903        struct foo_t *return_struct_pointer_example();
904
905       Perl code:
906
907        $ffi->attach( return_struct_pointer_example => [] => 'foo_t*' );
908        my $foo = return_struct_pointer_example();
909        # $foo is a copy of the record returned by the function.
910
911       As with strings, if the API expects you to free the record it returns
912       (it is misbehaving a little, but lets set that aside), then you can
913       work around this by returning an "opaque" type, casting to the record,
914       and finally freeing the original pointer.
915
916        use FFI::Platypus::Memory qw( free );
917        $ffi->attach( return_struct_pointer_example => [] => 'opaque' );
918        my $foo_ptr = return_struct_pointer_example();
919        my $foo = $ffi->cast( 'opaque' => 'foo_t*', $foo_ptr );
920        free $foo_ptr;
921
922       You can pass records into a closure, but care needs to be taken.
923       Records passed into a closure are read-only inside the closure,
924       including "string rw" members.  Although you can pass a "pointer" to a
925       record into a closure, because of limitations of the implementation you
926       actually have a copy, so all records passed into closures are passed
927       by-value.
928
929   Fixed length arrays
930       Fixed length arrays of native types and strings are supported by
931       FFI::Platypus.  Like pointers, if the values contained in the array are
932       updated by the C function these changes will be reflected when it
933       returns to Perl space.  An example of using this is the Unix "pipe"
934       command which returns a list of two file descriptors as an array.
935
936        use FFI::Platypus 1.00;
937
938        my $ffi = FFI::Platypus->new( api => 1 );
939        $ffi->lib(undef);
940        $ffi->attach([pipe=>'mypipe'] => ['int[2]'] => 'int');
941
942        my @fd = (0,0);
943        mypipe(\@fd);
944        my($fd1,$fd2) = @fd;
945
946        print "$fd1 $fd2\n";
947
948       Because of the way records are implemented, an array of records does
949       not make sense and is not currently supported.
950
951   Variable length arrays
952       [version 0.22]
953
954       Variable length arrays are supported for argument types can also be
955       specified by using the "[]" notation but by leaving the size empty:
956
957        $ffi->type('int[]' => 'var_int_array');
958
959       When used as an argument type it will probe the array reference that
960       you pass in to determine the correct size.  Usually you will need to
961       communicate the size of the array to the C code.  One way to do this is
962       to pass the length of the array in as an additional argument.  For
963       example the C code:
964
965        int
966        sum(int *array, int size)
967        {
968          int total, i;
969          for (i = 0, total = 0; i < size; i++)
970          {
971            total += array[i];
972          }
973          return total;
974        }
975
976       Can be called from Perl like this:
977
978        use FFI::Platypus 1.00;
979
980        my $ffi = FFI::Platypus->new( api => 1 );
981        $ffi->lib('./var_array.so');
982
983        $ffi->attach( sum => [ 'int[]', 'int' ] => 'int' );
984
985        my @list = (1..100);
986
987        print sum(\@list, scalar @list), "\n";
988
989       Another method might be to have a special value, such as 0 or NULL
990       indicate the termination of the array.
991
992       Because of the way records are implemented, an array of records does
993       not make sense and is not currently supported.
994
995   Closures
996       A closure (sometimes called a "callback", we use the "libffi"
997       terminology) is a Perl subroutine that can be called from C.  In order
998       to be called from C it needs to be passed to a C function.  To define
999       the closure type you need to provide a list of argument types and a
1000       return type.  Currently only native types (integers, floating point
1001       values, opaque), strings and records (by-value; you can pass a pointer
1002       to a record, but due to limitations of the record implementation this
1003       is actually a copy) are supported as closure argument types, and only
1004       native types and records (by-value; pointer records and records with
1005       string pointers cannot be returned from a closure) are supported as
1006       closure return types.  Inside the closure any records passed in are
1007       read-only.
1008
1009       We plan to add other types, though they can be converted using the
1010       Platypus "cast" or "attach_cast" methods.
1011
1012       Here is an example, with C code:
1013
1014        /*
1015         * closure.c - on Linux compile with: gcc closure.c -shared -o closure.so -fPIC
1016         */
1017
1018        #include <stdio.h>
1019
1020        typedef int (*closure_t)(int);
1021        closure_t my_closure = NULL;
1022
1023        void set_closure(closure_t value)
1024        {
1025          my_closure = value;
1026        }
1027
1028        int call_closure(int value)
1029        {
1030          if(my_closure != NULL)
1031            return my_closure(value);
1032          else
1033            fprintf(stderr, "closure is NULL\n");
1034        }
1035
1036       And the Perl code:
1037
1038        use FFI::Platypus 1.00;
1039
1040        my $ffi = FFI::Platypus->new( api => 1 );
1041        $ffi->lib('./closure.so');
1042        $ffi->type('(int)->int' => 'closure_t');
1043
1044        $ffi->attach(set_closure => ['closure_t'] => 'void');
1045        $ffi->attach(call_closure => ['int'] => 'int');
1046
1047        my $closure1 = $ffi->closure(sub { $_[0] * 2 });
1048        set_closure($closure1);
1049        print  call_closure(2), "\n"; # prints "4"
1050
1051        my $closure2 = $ffi->closure(sub { $_[0] * 4 });
1052        set_closure($closure2);
1053        print call_closure(2), "\n"; # prints "8"
1054
1055       If you have a pointer to a function in the form of an "opaque" type,
1056       you can pass this in place of a closure type:
1057
1058        use FFI::Platypus 1.00;
1059
1060        my $ffi = FFI::Platypus->new( api => 1 );
1061        $ffi->lib('./closure.so');
1062        $ffi->type('(int)->int' => 'closure_t');
1063
1064        $ffi->attach(set_closure => ['closure_t'] => 'void');
1065        $ffi->attach(call_closure => ['int'] => 'int');
1066
1067        my $closure = $ffi->closure(sub { $_[0] * 6 });
1068        my $opaque = $ffi->cast(closure_t => 'opaque', $closure);
1069        set_closure($opaque);
1070        print call_closure(2), "\n"; # prints "12"
1071
1072       The syntax for specifying a closure type is a list of comma separated
1073       types in parentheticals followed by a narrow arrow "->", followed by
1074       the return type for the closure.  For example a closure that takes a
1075       pointer, an integer and a string and returns an integer would look like
1076       this:
1077
1078        $ffi->type('(opaque, int, string) -> int' => 'my_closure_type');
1079
1080       Care needs to be taken with scoping and closures, because of the way
1081       Perl and C handle responsibility for allocating memory differently.
1082       Perl keeps reference counts and frees objects when nothing is
1083       referencing them.  In C the code that allocates the memory is
1084       considered responsible for explicitly free'ing the memory for objects
1085       it has created when they are no longer needed.  When you pass a closure
1086       into a C function, the C code has a pointer or reference to that
1087       object, but it has no way up letting Perl know when it is no longer
1088       using it. As a result, if you do not keep a reference to your closure
1089       around it will be free'd by Perl and if the C code ever tries to call
1090       the closure it will probably SIGSEGV.  Thus supposing you have a C
1091       function "set_closure" that takes a Perl closure, this is almost always
1092       wrong:
1093
1094        set_closure($ffi->closure({ $_[0] * 2 }));  # BAD
1095
1096       In some cases, you may want to create a closure shouldn't ever be
1097       free'd.  For example you are passing a closure into a C function that
1098       will retain it for the lifetime of your application.  You can use the
1099       sticky method to keep the closure, without the need to keep a reference
1100       of the closure:
1101
1102        {
1103          my $closure = $ffi->closure(sub { $_[0] * 2 });
1104          $closure->sticky;
1105          set_closure($closure); # OKAY
1106        }
1107        # closure still exists and is accesible from C, but
1108        # not from Perl land.
1109
1110   Custom Types
1111       Custom Types in Perl
1112
1113       Platypus custom types are the rough analogue to typemaps in the XS
1114       world.  They offer a method for converting Perl types into native types
1115       that the "libffi" can understand and pass on to the C code.
1116
1117       Example 1: Integer constants
1118
1119       Say you have a C header file like this:
1120
1121        /* possible foo types: */
1122        #define FOO_STATIC  1
1123        #define FOO_DYNAMIC 2
1124        #define FOO_OTHER   3
1125
1126        typedef int foo_t;
1127
1128        void foo(foo_t foo);
1129        foo_t get_foo();
1130
1131       The challenge is here that once the source is processed by the C pre-
1132       processor the name/value mappings for these "FOO_" constants are lost.
1133       There is no way to fetch them from the library once it is compiled and
1134       linked.
1135
1136       One common way of implementing this would be to create and export
1137       constants in your Perl module, like this:
1138
1139        package Foo;
1140
1141        use FFI::Platypus 1.00;
1142        use Exporter qw( import );
1143
1144        our @EXPORT_OK = qw( FOO_STATIC FOO_DYNAMIC FOO_OTHER foo get_foo );
1145
1146        use constant FOO_STATIC  => 1;
1147        use constant FOO_DYNAMIC => 2;
1148        use constant FOO_OTHER   => 3;
1149
1150        my $ffi = FFI::Platypus->new( api => 1 );
1151        $ffi->attach(foo     => ['int'] => 'void');
1152        $ffi->attach(get_foo => []      => 'int');
1153
1154       Then you could use the module thus:
1155
1156        use Foo qw( foo FOO_STATIC );
1157        foo(FOO_STATIC);
1158
1159       If you didn't want to rely on integer constants or exports, you could
1160       also define a custom type, and allow strings to be passed into your
1161       function, like this:
1162
1163        package Foo;
1164
1165        use FFI::Platypus 1.00;
1166
1167        our @EXPORT_OK = qw( foo get_foo );
1168
1169        my %foo_types = (
1170          static  => 1,
1171          dynamic => 2,
1172          other   => 3,
1173        );
1174        my %foo_types_reverse = reverse %foo_types;
1175
1176        my $ffi = FFI::Platypus->new( api => 1 );
1177        $ffi->custom_type(foo_t => {
1178          native_type    => 'int',
1179          native_to_perl => sub {
1180            $foo_types{$_[0]};
1181          },
1182          perl_to_native => sub {
1183            $foo_types_reverse{$_[0]};
1184          },
1185        });
1186
1187        $ffi->attach(foo     => ['foo_t'] => 'void');
1188        $ffi->attach(get_foo => []        => 'foo_t');
1189
1190       Now when an argument of type "foo_t" is called for it will be converted
1191       from an appropriate string representation, and any function that
1192       returns a "foo_t" type will return a string instead of the integer
1193       representation:
1194
1195        use Foo;
1196        foo('static');
1197
1198       If the library that you are using has a lot of these constants you can
1199       try using Convert::Binary::C or another C header parser to obtain the
1200       appropriate name/value pairings for the constants that you need.
1201
1202       Example 2: Blessed references
1203
1204       Supposing you have a C library that uses an opaque pointer with a
1205       pseudo OO interface, like this:
1206
1207        typedef struct foo_t;
1208
1209        foo_t *foo_new();
1210        void foo_method(foo_t *, int argument);
1211        void foo_free(foo_t *);
1212
1213       One approach to adapting this to Perl would be to create a OO Perl
1214       interface like this:
1215
1216        package Foo;
1217
1218        use FFI::Platypus 1.00;
1219        use FFI::Platypus::API qw( arguments_get_string );
1220
1221        my $ffi = FFI::Platypus->new( api => 1 );
1222        $ffi->custom_type(foo_t => {
1223          native_type    => 'opaque',
1224          native_to_perl => sub {
1225            my $class = arguments_get_string(0);
1226            bless \$_[0], $class;
1227          }
1228          perl_to_native => sub { ${$_[0]} },
1229        });
1230
1231        $ffi->attach([ foo_new => 'new' ] => [ 'string' ] => 'foo_t' );
1232        $ffi->attach([ foo_method => 'method' ] => [ 'foo_t', 'int' ] => 'void');
1233        $ffi->attach([ foo_free => 'DESTROY' ] => [ 'foo_t' ] => 'void');
1234
1235        my $foo = Foo->new;
1236
1237       Here we are blessing a reference to the opaque pointer when we return
1238       the custom type for "foo_t", and dereferencing that reference before we
1239       pass it back in.  The function "arguments_get_string" queries the C
1240       arguments to get the class name to make sure the object is blessed into
1241       the correct class (for more details on the custom type API see
1242       FFI::Platypus::API), so you can inherit and extend this class like a
1243       normal Perl class.  This works because the C "constructor" ignores the
1244       class name that we pass in as the first argument.  If you have a C
1245       "constructor" like this that takes arguments you'd have to write a
1246       wrapper for new.
1247
1248       A good example of a C library that uses this pattern, including
1249       inheritance is "libarchive". Platypus comes with a more extensive
1250       example in "examples/archive.pl" that demonstrates this.
1251
1252       Example 3: Pointers with pack / unpack
1253
1254       TODO
1255
1256       See example FFI::Platypus::Type::StringPointer.
1257
1258       Example 4: Custom Type modules and the Custom Type API
1259
1260       TODO
1261
1262       See example FFI::Platypus::Type::PointerSizeBuffer.
1263
1264       Example 5: Custom Type on CPAN
1265
1266       You can distribute your own Platypus custom types on CPAN, if you think
1267       they may be applicable to others.  The default namespace is prefix with
1268       "FFI::Platypus::Type::", though you can stick it anywhere (under your
1269       own namespace may make more sense if the custom type is specific to
1270       your application).
1271
1272       A good example and pattern to follow is
1273       FFI::Platypus::Type::StringArray.
1274

SEE ALSO

1276       FFI::Platypus
1277           Main platypus documentation.
1278
1279       FFI::Platypus::API
1280           Custom types API.
1281
1282       FFI::Platypus::Type::StringPointer
1283           String pointer type.
1284

AUTHOR

1286       Author: Graham Ollis <plicease@cpan.org>
1287
1288       Contributors:
1289
1290       Bakkiaraj Murugesan (bakkiaraj)
1291
1292       Dylan Cali (calid)
1293
1294       pipcet
1295
1296       Zaki Mughal (zmughal)
1297
1298       Fitz Elliott (felliott)
1299
1300       Vickenty Fesunov (vyf)
1301
1302       Gregor Herrmann (gregoa)
1303
1304       Shlomi Fish (shlomif)
1305
1306       Damyan Ivanov
1307
1308       Ilya Pavlov (Ilya33)
1309
1310       Petr Písař (ppisar)
1311
1312       Mohammad S Anwar (MANWAR)
1313
1314       Håkon Hægland (hakonhagland, HAKONH)
1315
1316       Meredith (merrilymeredith, MHOWARD)
1317
1318       Diab Jerius (DJERIUS)
1319
1320       Eric Brine (IKEGAMI)
1321
1322       szTheory
1323
1324       José Joaquín Atria (JJATRIA)
1325
1326       Pete Houston (openstrike, HOUSTON)
1327
1329       This software is copyright (c) 2015,2016,2017,2018,2019,2020 by Graham
1330       Ollis.
1331
1332       This is free software; you can redistribute it and/or modify it under
1333       the same terms as the Perl 5 programming language system itself.
1334
1335
1336
1337perl v5.34.0                      2021-10-29            FFI::Platypus::Type(3)
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