1H2XS(1)                Perl Programmers Reference Guide                H2XS(1)
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4

NAME

6       h2xs - convert .h C header files to Perl extensions
7

SYNOPSIS

9       h2xs [OPTIONS ...] [headerfile ... [extra_libraries]]
10
11       h2xs -h|-?|--help
12

DESCRIPTION

14       h2xs builds a Perl extension from C header files.  The extension will
15       include functions which can be used to retrieve the value of any
16       #define statement which was in the C header files.
17
18       The module_name will be used for the name of the extension.  If
19       module_name is not supplied then the name of the first header file will
20       be used, with the first character capitalized.
21
22       If the extension might need extra libraries, they should be included
23       here.  The extension Makefile.PL will take care of checking whether the
24       libraries actually exist and how they should be loaded.  The extra
25       libraries should be specified in the form -lm -lposix, etc, just as on
26       the cc command line.  By default, the Makefile.PL will search through
27       the library path determined by Configure.  That path can be augmented
28       by including arguments of the form -L/another/library/path in the
29       extra-libraries argument.
30
31       In spite of its name, h2xs may also be used to create a skeleton pure
32       Perl module. See the -X option.
33

OPTIONS

35       -A, --omit-autoload
36            Omit all autoload facilities.  This is the same as -c but also
37            removes the "use AutoLoader" statement from the .pm file.
38
39       -B, --beta-version
40            Use an alpha/beta style version number.  Causes version number to
41            be "0.00_01" unless -v is specified.
42
43       -C, --omit-changes
44            Omits creation of the Changes file, and adds a HISTORY section to
45            the POD template.
46
47       -F, --cpp-flags=addflags
48            Additional flags to specify to C preprocessor when scanning header
49            for function declarations.  Writes these options in the generated
50            Makefile.PL too.
51
52       -M, --func-mask=regular expression
53            selects functions/macros to process.
54
55       -O, --overwrite-ok
56            Allows a pre-existing extension directory to be overwritten.
57
58       -P, --omit-pod
59            Omit the autogenerated stub POD section.
60
61       -X, --omit-XS
62            Omit the XS portion. Used to generate a skeleton pure Perl module.
63            "-c" and "-f" are implicitly enabled.
64
65       -a, --gen-accessors
66            Generate an accessor method for each element of structs and
67            unions. The generated methods are named after the element name;
68            will return the current value of the element if called without
69            additional arguments; and will set the element to the supplied
70            value (and return the new value) if called with an additional
71            argument. Embedded structures and unions are returned as a pointer
72            rather than the complete structure, to facilitate chained calls.
73
74            These methods all apply to the Ptr type for the structure;
75            additionally two methods are constructed for the structure type
76            itself, "_to_ptr" which returns a Ptr type pointing to the same
77            structure, and a "new" method to construct and return a new
78            structure, initialised to zeroes.
79
80       -b, --compat-version=version
81            Generates a .pm file which is backwards compatible with the
82            specified perl version.
83
84            For versions < 5.6.0, the changes are.
85                - no use of 'our' (uses 'use vars' instead)
86                - no 'use warnings'
87
88            Specifying a compatibility version higher than the version of perl
89            you are using to run h2xs will have no effect.  If unspecified
90            h2xs will default to compatibility with the version of perl you
91            are using to run h2xs.
92
93       -c, --omit-constant
94            Omit "constant()" from the .xs file and corresponding specialised
95            "AUTOLOAD" from the .pm file.
96
97       -d, --debugging
98            Turn on debugging messages.
99
100       -e, --omit-enums=[regular expression]
101            If regular expression is not given, skip all constants that are
102            defined in a C enumeration. Otherwise skip only those constants
103            that are defined in an enum whose name matches regular expression.
104
105            Since regular expression is optional, make sure that this switch
106            is followed by at least one other switch if you omit regular
107            expression and have some pending arguments such as header-file
108            names. This is ok:
109
110                h2xs -e -n Module::Foo foo.h
111
112            This is not ok:
113
114                h2xs -n Module::Foo -e foo.h
115
116            In the latter, foo.h is taken as regular expression.
117
118       -f, --force
119            Allows an extension to be created for a header even if that header
120            is not found in standard include directories.
121
122       -g, --global
123            Include code for safely storing static data in the .xs file.
124            Extensions that do no make use of static data can ignore this
125            option.
126
127       -h, -?, --help
128            Print the usage, help and version for this h2xs and exit.
129
130       -k, --omit-const-func
131            For function arguments declared as "const", omit the const
132            attribute in the generated XS code.
133
134       -m, --gen-tied-var
135            Experimental: for each variable declared in the header file(s),
136            declare a perl variable of the same name magically tied to the C
137            variable.
138
139       -n, --name=module_name
140            Specifies a name to be used for the extension, e.g., -n RPC::DCE
141
142       -o, --opaque-re=regular expression
143            Use "opaque" data type for the C types matched by the regular
144            expression, even if these types are "typedef"-equivalent to types
145            from typemaps.  Should not be used without -x.
146
147            This may be useful since, say, types which are
148            "typedef"-equivalent to integers may represent OS-related handles,
149            and one may want to work with these handles in OO-way, as in
150            "$handle->do_something()".  Use "-o ." if you want to handle all
151            the "typedef"ed types as opaque types.
152
153            The type-to-match is whitewashed (except for commas, which have no
154            whitespace before them, and multiple "*" which have no whitespace
155            between them).
156
157       -p, --remove-prefix=prefix
158            Specify a prefix which should be removed from the Perl function
159            names, e.g., -p sec_rgy_ This sets up the XS PREFIX keyword and
160            removes the prefix from functions that are autoloaded via the
161            "constant()" mechanism.
162
163       -s, --const-subs=sub1,sub2
164            Create a perl subroutine for the specified macros rather than
165            autoload with the constant() subroutine.  These macros are assumed
166            to have a return type of char *, e.g.,
167            -s sec_rgy_wildcard_name,sec_rgy_wildcard_sid.
168
169       -t, --default-type=type
170            Specify the internal type that the constant() mechanism uses for
171            macros.  The default is IV (signed integer).  Currently all macros
172            found during the header scanning process will be assumed to have
173            this type.  Future versions of "h2xs" may gain the ability to make
174            educated guesses.
175
176       --use-new-tests
177            When --compat-version (-b) is present the generated tests will use
178            "Test::More" rather than "Test" which is the default for versions
179            before 5.6.2.  "Test::More" will be added to PREREQ_PM in the
180            generated "Makefile.PL".
181
182       --use-old-tests
183            Will force the generation of test code that uses the older "Test"
184            module.
185
186       --skip-exporter
187            Do not use "Exporter" and/or export any symbol.
188
189       --skip-ppport
190            Do not use "Devel::PPPort": no portability to older version.
191
192       --skip-autoloader
193            Do not use the module "AutoLoader"; but keep the constant()
194            function and "sub AUTOLOAD" for constants.
195
196       --skip-strict
197            Do not use the pragma "strict".
198
199       --skip-warnings
200            Do not use the pragma "warnings".
201
202       -v, --version=version
203            Specify a version number for this extension.  This version number
204            is added to the templates.  The default is 0.01, or 0.00_01 if
205            "-B" is specified.  The version specified should be numeric.
206
207       -x, --autogen-xsubs
208            Automatically generate XSUBs basing on function declarations in
209            the header file.  The package "C::Scan" should be installed. If
210            this option is specified, the name of the header file may look
211            like "NAME1,NAME2". In this case NAME1 is used instead of the
212            specified string, but XSUBs are emitted only for the declarations
213            included from file NAME2.
214
215            Note that some types of arguments/return-values for functions may
216            result in XSUB-declarations/typemap-entries which need hand-
217            editing. Such may be objects which cannot be converted from/to a
218            pointer (like "long long"), pointers to functions, or arrays.  See
219            also the section on "LIMITATIONS of -x".
220

EXAMPLES

222           # Default behavior, extension is Rusers
223           h2xs rpcsvc/rusers
224
225           # Same, but extension is RUSERS
226           h2xs -n RUSERS rpcsvc/rusers
227
228           # Extension is rpcsvc::rusers. Still finds <rpcsvc/rusers.h>
229           h2xs rpcsvc::rusers
230
231           # Extension is ONC::RPC.  Still finds <rpcsvc/rusers.h>
232           h2xs -n ONC::RPC rpcsvc/rusers
233
234           # Without constant() or AUTOLOAD
235           h2xs -c rpcsvc/rusers
236
237           # Creates templates for an extension named RPC
238           h2xs -cfn RPC
239
240           # Extension is ONC::RPC.
241           h2xs -cfn ONC::RPC
242
243           # Extension is a pure Perl module with no XS code.
244           h2xs -X My::Module
245
246           # Extension is Lib::Foo which works at least with Perl5.005_03.
247           # Constants are created for all #defines and enums h2xs can find
248           # in foo.h.
249           h2xs -b 5.5.3 -n Lib::Foo foo.h
250
251           # Extension is Lib::Foo which works at least with Perl5.005_03.
252           # Constants are created for all #defines but only for enums
253           # whose names do not start with 'bar_'.
254           h2xs -b 5.5.3 -e '^bar_' -n Lib::Foo foo.h
255
256           # Makefile.PL will look for library -lrpc in
257           # additional directory /opt/net/lib
258           h2xs rpcsvc/rusers -L/opt/net/lib -lrpc
259
260           # Extension is DCE::rgynbase
261           # prefix "sec_rgy_" is dropped from perl function names
262           h2xs -n DCE::rgynbase -p sec_rgy_ dce/rgynbase
263
264           # Extension is DCE::rgynbase
265           # prefix "sec_rgy_" is dropped from perl function names
266           # subroutines are created for sec_rgy_wildcard_name and
267           # sec_rgy_wildcard_sid
268           h2xs -n DCE::rgynbase -p sec_rgy_ \
269           -s sec_rgy_wildcard_name,sec_rgy_wildcard_sid dce/rgynbase
270
271           # Make XS without defines in perl.h, but with function declarations
272           # visible from perl.h. Name of the extension is perl1.
273           # When scanning perl.h, define -DEXT=extern -DdEXT= -DINIT(x)=
274           # Extra backslashes below because the string is passed to shell.
275           # Note that a directory with perl header files would
276           #  be added automatically to include path.
277           h2xs -xAn perl1 -F "-DEXT=extern -DdEXT= -DINIT\(x\)=" perl.h
278
279           # Same with function declaration in proto.h as visible from perl.h.
280           h2xs -xAn perl2 perl.h,proto.h
281
282           # Same but select only functions which match /^av_/
283           h2xs -M '^av_' -xAn perl2 perl.h,proto.h
284
285           # Same but treat SV* etc as "opaque" types
286           h2xs -o '^[S]V \*$' -M '^av_' -xAn perl2 perl.h,proto.h
287
288   Extension based on .h and .c files
289       Suppose that you have some C files implementing some functionality, and
290       the corresponding header files.  How to create an extension which makes
291       this functionality accessible in Perl?  The example below assumes that
292       the header files are interface_simple.h and interface_hairy.h, and you
293       want the perl module be named as "Ext::Ension".  If you need some
294       preprocessor directives and/or linking with external libraries, see the
295       flags "-F", "-L" and "-l" in "OPTIONS".
296
297       Find the directory name
298           Start with a dummy run of h2xs:
299
300             h2xs -Afn Ext::Ension
301
302           The only purpose of this step is to create the needed directories,
303           and let you know the names of these directories.  From the output
304           you can see that the directory for the extension is Ext/Ension.
305
306       Copy C files
307           Copy your header files and C files to this directory Ext/Ension.
308
309       Create the extension
310           Run h2xs, overwriting older autogenerated files:
311
312             h2xs -Oxan Ext::Ension interface_simple.h interface_hairy.h
313
314           h2xs looks for header files after changing to the extension
315           directory, so it will find your header files OK.
316
317       Archive and test
318           As usual, run
319
320             cd Ext/Ension
321             perl Makefile.PL
322             make dist
323             make
324             make test
325
326       Hints
327           It is important to do "make dist" as early as possible.  This way
328           you can easily merge(1) your changes to autogenerated files if you
329           decide to edit your ".h" files and rerun h2xs.
330
331           Do not forget to edit the documentation in the generated .pm file.
332
333           Consider the autogenerated files as skeletons only, you may invent
334           better interfaces than what h2xs could guess.
335
336           Consider this section as a guideline only, some other options of
337           h2xs may better suit your needs.
338

ENVIRONMENT

340       No environment variables are used.
341

AUTHOR

343       Larry Wall and others
344

SEE ALSO

346       perl, perlxstut, ExtUtils::MakeMaker, and AutoLoader.
347

DIAGNOSTICS

349       The usual warnings if it cannot read or write the files involved.
350

LIMITATIONS of -x

352       h2xs would not distinguish whether an argument to a C function which is
353       of the form, say, "int *", is an input, output, or input/output
354       parameter.  In particular, argument declarations of the form
355
356           int
357           foo(n)
358               int *n
359
360       should be better rewritten as
361
362           int
363           foo(n)
364               int &n
365
366       if "n" is an input parameter.
367
368       Additionally, h2xs has no facilities to intuit that a function
369
370          int
371          foo(addr,l)
372               char *addr
373               int   l
374
375       takes a pair of address and length of data at this address, so it is
376       better to rewrite this function as
377
378           int
379           foo(sv)
380                   SV *addr
381               PREINIT:
382                   STRLEN len;
383                   char *s;
384               CODE:
385                   s = SvPV(sv,len);
386                   RETVAL = foo(s, len);
387               OUTPUT:
388                   RETVAL
389
390       or alternately
391
392           static int
393           my_foo(SV *sv)
394           {
395               STRLEN len;
396               char *s = SvPV(sv,len);
397
398               return foo(s, len);
399           }
400
401           MODULE = foo        PACKAGE = foo   PREFIX = my_
402
403           int
404           foo(sv)
405               SV *sv
406
407       See perlxs and perlxstut for additional details.
408
409
410
411perl v5.34.0                      2021-10-18                           H2XS(1)
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