A file in XS format starts with a C language section which goes until the
first C<MODULE =Z<>> directive. Other XS directives and XSUB definitions
may follow this line. The "language" used in this part of the file
-is usually referred to as the XS language.
+is usually referred to as the XS language. B<xsubpp> recognizes and
+skips POD (see L<perlpod>) in both the C and XS language sections, which
+allows the XS file to contain embedded documentation.
See L<perlxstut> for a tutorial on the whole extension creation process.
Note: For some extensions, Dave Beazley's SWIG system may provide a
-significantly more convenient mechanism for creating the extension glue
-code. See L<http://www.swig.org> for more
-information.
+significantly more convenient mechanism for creating the extension
+glue code. See http://www.swig.org/ for more information.
=head2 On The Road
sin(x)
double x
-When using parameters with C pointer types, as in
+Optionally, one can merge the description of types and the list of
+argument names, rewriting this as
- double string_to_double(char *s);
+ double
+ sin(double x)
+
+This makes this XSUB look similar to an ANSI C declaration. An optional
+semicolon is allowed after the argument list, as in
+
+ double
+ sin(double x);
-there may be two ways to describe this argument to B<xsubpp>:
+Parameters with C pointer types can have different semantic: C functions
+with similar declarations
+
+ bool string_looks_as_a_number(char *s);
+ bool make_char_uppercase(char *c);
+
+are used in absolutely incompatible manner. Parameters to these functions
+could be described B<xsubpp> like this:
char * s
- char &s
+ char &c
Both these XS declarations correspond to the C<char*> C type, but they have
-different semantics. It is convenient to think that the indirection operator
+different semantics, see L<"The & Unary Operator">.
+
+It is convenient to think that the indirection operator
C<*> should be considered as a part of the type and the address operator C<&>
-should be considered part of the variable. See L<"The Typemap"> and
-L<"The & Unary Operator"> for more info about handling qualifiers and unary
-operators in C types.
+should be considered part of the variable. See L<"The Typemap">
+for more info about handling qualifiers and unary operators in C types.
The function name and the return type must be placed on
separate lines and should be flush left-adjusted.
double x sin(x)
double x
-The function body may be indented or left-adjusted. The following example
-shows a function with its body left-adjusted. Most examples in this
-document will indent the body for better readability.
+The rest of the function description may be indented or left-adjusted. The
+following example shows a function with its body left-adjusted. Most
+examples in this document will indent the body for better readability.
CORRECT
and "old-practice-declared-as-void" functions. Hence your code is at
mercy of this heuristics unless you use C<SV *> as return value.)
+=head2 Returning SVs, AVs and HVs through RETVAL
+
+When you're using RETVAL to return an C<SV *>, there's some magic
+going on behind the scenes that should be mentioned. When you're
+manipulating the argument stack using the ST(x) macro, for example,
+you usually have to pay special attention to reference counts. (For
+more about reference counts, see L<perlguts>.) To make your life
+easier, the typemap file automatically makes C<RETVAL> mortal when
+you're returning an C<SV *>. Thus, the following two XSUBs are more
+or less equivalent:
+
+ void
+ alpha()
+ PPCODE:
+ ST(0) = newSVpv("Hello World",0);
+ sv_2mortal(ST(0));
+ XSRETURN(1);
+
+ SV *
+ beta()
+ CODE:
+ RETVAL = newSVpv("Hello World",0);
+ OUTPUT:
+ RETVAL
+
+This is quite useful as it usually improves readability. While
+this works fine for an C<SV *>, it's unfortunately not as easy
+to have C<AV *> or C<HV *> as a return value. You I<should> be
+able to write:
+
+ AV *
+ array()
+ CODE:
+ RETVAL = newAV();
+ /* do something with RETVAL */
+ OUTPUT:
+ RETVAL
+
+But due to an unfixable bug (fixing it would break lots of existing
+CPAN modules) in the typemap file, the reference count of the C<AV *>
+is not properly decremented. Thus, the above XSUB would leak memory
+whenever it is being called. The same problem exists for C<HV *>.
+
+When you're returning an C<AV *> or a C<HV *>, you have make sure
+their reference count is decremented by making the AV or HV mortal:
+
+ AV *
+ array()
+ CODE:
+ RETVAL = newAV();
+ sv_2mortal((SV*)RETVAL);
+ /* do something with RETVAL */
+ OUTPUT:
+ RETVAL
+
+And also remember that you don't have to do this for an C<SV *>.
+
=head2 The MODULE Keyword
-The MODULE keyword is used to start the XS code and to
-specify the package of the functions which are being
-defined. All text preceding the first MODULE keyword is
-considered C code and is passed through to the output
-untouched. Every XS module will have a bootstrap function
-which is used to hook the XSUBs into Perl. The package name
-of this bootstrap function will match the value of the last
-MODULE statement in the XS source files. The value of
-MODULE should always remain constant within the same XS
-file, though this is not required.
+The MODULE keyword is used to start the XS code and to specify the package
+of the functions which are being defined. All text preceding the first
+MODULE keyword is considered C code and is passed through to the output with
+POD stripped, but otherwise untouched. Every XS module will have a
+bootstrap function which is used to hook the XSUBs into Perl. The package
+name of this bootstrap function will match the value of the last MODULE
+statement in the XS source files. The value of MODULE should always remain
+constant within the same XS file, though this is not required.
The following example will start the XS code and will place
all functions in a package named RPC.
[ XS code in package RPC ]
+The same package name can be used more than once, allowing for
+non-contiguous code. This is useful if you have a stronger ordering
+principle than package names.
+
Although this keyword is optional and in some cases provides redundant
information it should always be used. This keyword will ensure that the
XSUBs appear in the desired package.
remainder of the OUTPUT section. See L<perlguts> for more details
about 'set' magic.
+=head2 The NO_OUTPUT Keyword
+
+The NO_OUTPUT can be placed as the first token of the XSUB. This keyword
+indicates that while the C subroutine we provide an interface to has
+a non-C<void> return type, the return value of this C subroutine should not
+be returned from the generated Perl subroutine.
+
+With this keyword present L<The RETVAL Variable> is created, and in the
+generated call to the subroutine this variable is assigned to, but the value
+of this variable is not going to be used in the auto-generated code.
+
+This keyword makes sense only if C<RETVAL> is going to be accessed by the
+user-supplied code. It is especially useful to make a function interface
+more Perl-like, especially when the C return value is just an error condition
+indicator. For example,
+
+ NO_OUTPUT int
+ delete_file(char *name)
+ POSTCALL:
+ if (RETVAL != 0)
+ croak("Error %d while deleting file '%s'", RETVAL, name);
+
+Here the generated XS function returns nothing on success, and will die()
+with a meaningful error message on error.
+
=head2 The CODE: Keyword
This keyword is used in more complicated XSUBs which require
=head2 The PREINIT: Keyword
The PREINIT: keyword allows extra variables to be declared immediately
-before or after the declartions of the parameters from the INPUT: section
+before or after the declarations of the parameters from the INPUT: section
are emitted.
If a variable is declared inside a CODE: section it will follow any typemap
C<h = host> is not performed too early. Otherwise one would need to have the
assignment C<h = host> in a CODE: or INIT: section.)
+=head2 The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords
+
+In the list of parameters for an XSUB, one can precede parameter names
+by the C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> keywords.
+C<IN> keyword is the default, the other keywords indicate how the Perl
+interface should differ from the C interface.
+
+Parameters preceded by C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT>
+keywords are considered to be used by the C subroutine I<via
+pointers>. C<OUTLIST>/C<OUT> keywords indicate that the C subroutine
+does not inspect the memory pointed by this parameter, but will write
+through this pointer to provide additional return values.
+
+Parameters preceded by C<OUTLIST> keyword do not appear in the usage
+signature of the generated Perl function.
+
+Parameters preceded by C<IN_OUTLIST>/C<IN_OUT>/C<OUT> I<do> appear as
+parameters to the Perl function. With the exception of
+C<OUT>-parameters, these parameters are converted to the corresponding
+C type, then pointers to these data are given as arguments to the C
+function. It is expected that the C function will write through these
+pointers.
+
+The return list of the generated Perl function consists of the C return value
+from the function (unless the XSUB is of C<void> return type or
+C<The NO_OUTPUT Keyword> was used) followed by all the C<OUTLIST>
+and C<IN_OUTLIST> parameters (in the order of appearance). On the
+return from the XSUB the C<IN_OUT>/C<OUT> Perl parameter will be
+modified to have the values written by the C function.
+
+For example, an XSUB
+
+ void
+ day_month(OUTLIST day, IN unix_time, OUTLIST month)
+ int day
+ int unix_time
+ int month
+
+should be used from Perl as
+
+ my ($day, $month) = day_month(time);
+
+The C signature of the corresponding function should be
+
+ void day_month(int *day, int unix_time, int *month);
+
+The C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<IN_OUT>/C<OUT> keywords can be
+mixed with ANSI-style declarations, as in
+
+ void
+ day_month(OUTLIST int day, int unix_time, OUTLIST int month)
+
+(here the optional C<IN> keyword is omitted).
+
+The C<IN_OUT> parameters are identical with parameters introduced with
+L<The & Unary Operator> and put into the C<OUTPUT:> section (see
+L<The OUTPUT: Keyword>). The C<IN_OUTLIST> parameters are very similar,
+the only difference being that the value C function writes through the
+pointer would not modify the Perl parameter, but is put in the output
+list.
+
+The C<OUTLIST>/C<OUT> parameter differ from C<IN_OUTLIST>/C<IN_OUT>
+parameters only by the initial value of the Perl parameter not
+being read (and not being given to the C function - which gets some
+garbage instead). For example, the same C function as above can be
+interfaced with as
+
+ void day_month(OUT int day, int unix_time, OUT int month);
+
+or
+
+ void
+ day_month(day, unix_time, month)
+ int &day = NO_INIT
+ int unix_time
+ int &month = NO_INIT
+ OUTPUT:
+ day
+ month
+
+However, the generated Perl function is called in very C-ish style:
+
+ my ($day, $month);
+ day_month($day, time, $month);
+
+=head2 The C<length(NAME)> Keyword
+
+If one of the input arguments to the C function is the length of a string
+argument C<NAME>, one can substitute the name of the length-argument by
+C<length(NAME)> in the XSUB declaration. This argument must be omitted when
+the generated Perl function is called. E.g.,
+
+ void
+ dump_chars(char *s, short l)
+ {
+ short n = 0;
+ while (n < l) {
+ printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]);
+ n++;
+ }
+ }
+
+ MODULE = x PACKAGE = x
+
+ void dump_chars(char *s, short length(s))
+
+should be called as C<dump_chars($string)>.
+
+This directive is supported with ANSI-type function declarations only.
+
=head2 Variable-length Parameter Lists
XSUBs can have variable-length parameter lists by specifying an ellipsis
Some people may be inclined to include an explicit C<return> in the above
XSUB, rather than letting control fall through to the end. In those
situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that
-the XSUB stack is properly adjusted. Consult L<perlguts/"API LISTING"> for
-other C<XSRETURN> macros.
+the XSUB stack is properly adjusted. Consult L<perlapi> for other
+C<XSRETURN> macros.
Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can
rewrite this example as:
OUTPUT:
RETVAL
-In fact, one can put this check into a CLEANUP: section as well. Together
+In fact, one can put this check into a POSTCALL: section as well. Together
with PREINIT: simplifications, this leads to:
int
rpcb_gettime(host)
char *host
time_t timep;
- CLEANUP:
+ POSTCALL:
if (RETVAL == 0)
XSRETURN_UNDEF;
code specified for the cleanup block will be added as the last statements
in the XSUB.
+=head2 The POSTCALL: Keyword
+
+This keyword can be used when an XSUB requires special procedures
+executed after the C subroutine call is performed. When the POSTCALL:
+keyword is used it must precede OUTPUT: and CLEANUP: blocks which are
+present in the XSUB.
+
+See examples in L<"The NO_OUTPUT Keyword"> and L<"Returning Undef And Empty Lists">.
+
+The POSTCALL: block does not make a lot of sense when the C subroutine
+call is supplied by user by providing either CODE: or PPCODE: section.
+
=head2 The BOOT: Keyword
The BOOT: keyword is used to add code to the extension's bootstrap
timep
RETVAL
+If the prototypes are enabled, you can disable it locally for a given
+XSUB as in the following example:
+
+ void
+ rpcb_gettime_noproto()
+ PROTOTYPE: DISABLE
+ ...
+
=head2 The ALIAS: Keyword
The ALIAS: keyword allows an XSUB to have two or more unique Perl names
OUTPUT:
timep
+=head2 The OVERLOAD: Keyword
+
+Instead of writing an overloaded interface using pure Perl, you
+can also use the OVERLOAD keyword to define additional Perl names
+for your functions (like the ALIAS: keyword above). However, the
+overloaded functions must be defined with three parameters (except
+for the nomethod() function which needs four parameters). If any
+function has the OVERLOAD: keyword, several additional lines
+will be defined in the c file generated by xsubpp in order to
+register with the overload magic.
+
+Since blessed objects are actually stored as RV's, it is useful
+to use the typemap features to preprocess parameters and extract
+the actual SV stored within the blessed RV. See the sample for
+T_PTROBJ_SPECIAL below.
+
+To use the OVERLOAD: keyword, create an XS function which takes
+three input parameters ( or use the c style '...' definition) like
+this:
+
+ SV *
+ cmp (lobj, robj, swap)
+ My_Module_obj lobj
+ My_Module_obj robj
+ IV swap
+ OVERLOAD: cmp <=>
+ { /* function defined here */}
+
+In this case, the function will overload both of the three way
+comparison operators. For all overload operations using non-alpha
+characters, you must type the parameter without quoting, seperating
+multiple overloads with whitespace. Note that "" (the stringify
+overload) should be entered as \"\" (i.e. escaped).
+
+=head2 The FALLBACK: Keyword
+
+In addition to the OVERLOAD keyword, if you need to control how
+Perl autogenerates missing overloaded operators, you can set the
+FALLBACK keyword in the module header section, like this:
+
+ MODULE = RPC PACKAGE = RPC
+
+ FALLBACK: TRUE
+ ...
+
+where FALLBACK can take any of the three values TRUE, FALSE, or
+UNDEF. If you do not set any FALLBACK value when using OVERLOAD,
+it defaults to UNDEF. FALLBACK is not used except when one or
+more functions using OVERLOAD have been defined. Please see
+L<overload/Fallback> for more details.
+
=head2 The INTERFACE: Keyword
This keyword declares the current XSUB as a keeper of the given
This is useful to avoid a CODE: block for a C function which takes a parameter
by reference. Typically, the parameter should be not a pointer type (an
-C<int> or C<long> but not a C<int*> or C<long*>).
+C<int> or C<long> but not an C<int*> or C<long*>).
The following XSUB will generate incorrect C code. The B<xsubpp> compiler will
turn this into code which calls C<rpcb_gettime()> with parameters C<(char
OUTPUT:
timep
-=head2 Inserting Comments and C Preprocessor Directives
+=head2 Inserting POD, Comments and C Preprocessor Directives
-C preprocessor directives are allowed within BOOT:, PREINIT: INIT:,
-CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions.
-Comments are allowed anywhere after the MODULE keyword. The compiler
-will pass the preprocessor directives through untouched and will remove
-the commented lines.
+C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:,
+PPCODE:, POSTCALL:, and CLEANUP: blocks, as well as outside the functions.
+Comments are allowed anywhere after the MODULE keyword. The compiler will
+pass the preprocessor directives through untouched and will remove the
+commented lines. POD documentation is allowed at any point, both in the
+C and XS language sections. POD must be terminated with a C<=cut> command;
+C<xsubpp> will exit with an error if it does not. It is very unlikely that
+human generated C code will be mistaken for POD, as most indenting styles
+result in whitespace in front of any line starting with C<=>. Machine
+generated XS files may fall into this trap unless care is taken to
+ensure that a space breaks the sequence "\n=".
Comments can be added to XSUBs by placing a C<#> as the first
non-whitespace of a line. Care should be taken to avoid making the
candidates to return undef or an empty list in case of failure. If the
failure may be detected without a call to the C function, you may want to use
an INIT: section to report the failure. For failures detectable after the C
-function returns one may want to use a CLEANUP: section to process the
+function returns one may want to use a POSTCALL: section to process the
failure. In more complicated cases use CODE: or PPCODE: sections.
If many functions use the same failure indication based on the return value,
The typemap is a collection of code fragments which are used by the B<xsubpp>
compiler to map C function parameters and values to Perl values. The
-typemap file may consist of three sections labeled C<TYPEMAP>, C<INPUT>, and
+typemap file may consist of three sections labelled C<TYPEMAP>, C<INPUT>, and
C<OUTPUT>. An unlabelled initial section is assumed to be a C<TYPEMAP>
section. The INPUT section tells
the compiler how to translate Perl values
The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin
in the first column on a line by themselves, and must be in uppercase.
-The default typemap in the C<ext> directory of the Perl source contains many
-useful types which can be used by Perl extensions. Some extensions define
-additional typemaps which they keep in their own directory. These
-additional typemaps may reference INPUT and OUTPUT maps in the main
+The default typemap in the C<lib/ExtUtils> directory of the Perl source
+contains many useful types which can be used by Perl extensions. Some
+extensions define additional typemaps which they keep in their own directory.
+These additional typemaps may reference INPUT and OUTPUT maps in the main
typemap. The B<xsubpp> compiler will allow the extension's own typemap to
override any mappings which are in the default typemap.
T_PTROBJ_SPECIAL
if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) {
IV tmp = SvIV((SV*)SvRV($arg));
- $var = ($type) tmp;
+ $var = INT2PTR($type, tmp);
}
else
croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")
on the fly, giving the desired effect. This example demonstrates some
of the power and versatility of the typemap facility.
+The INT2PTR macro (defined in perl.h) casts an integer to a pointer,
+of a given type, taking care of the possible different size of integers
+and pointers. There are also PTR2IV, PTR2UV, PTR2NV macros,
+to map the other way, which may be useful in OUTPUT sections.
+
+=head2 Safely Storing Static Data in XS
+
+Starting with Perl 5.8, a macro framework has been defined to allow
+static data to be safely stored in XS modules that will be accessed from
+a multi-threaded Perl.
+
+Although primarily designed for use with multi-threaded Perl, the macros
+have been designed so that they will work with non-threaded Perl as well.
+
+It is therefore strongly recommended that these macros be used by all
+XS modules that make use of static data.
+
+The easiest way to get a template set of macros to use is by specifying
+the C<-g> (C<--global>) option with h2xs (see L<h2xs>).
+
+Below is an example module that makes use of the macros.
+
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
+
+ /* Global Data */
+
+ #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION
+
+ typedef struct {
+ int count;
+ char name[3][100];
+ } my_cxt_t;
+
+ START_MY_CXT
+
+ MODULE = BlindMice PACKAGE = BlindMice
+
+ BOOT:
+ {
+ MY_CXT_INIT;
+ MY_CXT.count = 0;
+ strcpy(MY_CXT.name[0], "None");
+ strcpy(MY_CXT.name[1], "None");
+ strcpy(MY_CXT.name[2], "None");
+ }
+
+ int
+ newMouse(char * name)
+ char * name;
+ PREINIT:
+ dMY_CXT;
+ CODE:
+ if (MY_CXT.count >= 3) {
+ warn("Already have 3 blind mice") ;
+ RETVAL = 0;
+ }
+ else {
+ RETVAL = ++ MY_CXT.count;
+ strcpy(MY_CXT.name[MY_CXT.count - 1], name);
+ }
+
+ char *
+ get_mouse_name(index)
+ int index
+ CODE:
+ dMY_CXT;
+ RETVAL = MY_CXT.lives ++;
+ if (index > MY_CXT.count)
+ croak("There are only 3 blind mice.");
+ else
+ RETVAL = newSVpv(MY_CXT.name[index - 1]);
+
+
+B<REFERENCE>
+
+=over 5
+
+=item MY_CXT_KEY
+
+This macro is used to define a unique key to refer to the static data
+for an XS module. The suggested naming scheme, as used by h2xs, is to
+use a string that consists of the module name, the string "::_guts"
+and the module version number.
+
+ #define MY_CXT_KEY "MyModule::_guts" XS_VERSION
+
+=item typedef my_cxt_t
+
+This struct typedef I<must> always be called C<my_cxt_t> -- the other
+C<CXT*> macros assume the existence of the C<my_cxt_t> typedef name.
+
+Declare a typedef named C<my_cxt_t> that is a structure that contains
+all the data that needs to be interpreter-local.
+
+ typedef struct {
+ int some_value;
+ } my_cxt_t;
+
+=item START_MY_CXT
+
+Always place the START_MY_CXT macro directly after the declaration
+of C<my_cxt_t>.
+
+=item MY_CXT_INIT
+
+The MY_CXT_INIT macro initialises storage for the C<my_cxt_t> struct.
+
+It I<must> be called exactly once -- typically in a BOOT: section.
+
+=item dMY_CXT
+
+Use the dMY_CXT macro (a declaration) in all the functions that access
+MY_CXT.
+
+=item MY_CXT
+
+Use the MY_CXT macro to access members of the C<my_cxt_t> struct. For
+example, if C<my_cxt_t> is
+
+ typedef struct {
+ int index;
+ } my_cxt_t;
+
+then use this to access the C<index> member
+
+ dMY_CXT;
+ MY_CXT.index = 2;
+
+=back
+
=head1 EXAMPLES
File C<RPC.xs>: Interface to some ONC+ RPC bind library functions.
Originally written by Dean Roehrich <F<roehrich@cray.com>>.
-Maintained since 1996 by The Perl Porters <F<perlbug@perl.com>>.
+Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>.
https://perl5.git.perl.org / perl5.git / blobdiff