PERLXS(1) Perl Programmers Reference Guide PERLXS(1)
NAME
perlxs - XS language reference manual
DESCRIPTION
Introduction
XS is an interface description file format used to create an extension interface between Perl and C code (or a
C library) which one wishes to use with Perl. The XS interface is combined with the library to create a new
library which can then be either dynamically loaded or statically linked into perl. The XS interface
description is written in the XS language and is the core component of the Perl extension interface.
An XSUB forms the basic unit of the XS interface. After compilation by the xsubpp compiler, each XSUB amounts
to a C function definition which will provide the glue between Perl calling conventions and C calling
conventions.
The glue code pulls the arguments from the Perl stack, converts these Perl values to the formats expected by a
C function, call this C function, transfers the return values of the C function back to Perl. Return values
here may be a conventional C return value or any C function arguments that may serve as output parameters.
These return values may be passed back to Perl either by putting them on the Perl stack, or by modifying the
arguments supplied from the Perl side.
The above is a somewhat simplified view of what really happens. Since Perl allows more flexible calling
conventions than C, XSUBs may do much more in practice, such as checking input parameters for validity,
throwing exceptions (or returning undef/empty list) if the return value from the C function indicates failure,
calling different C functions based on numbers and types of the arguments, providing an object-oriented
interface, etc.
Of course, one could write such glue code directly in C. However, this would be a tedious task, especially if
one needs to write glue for multiple C functions, and/or one is not familiar enough with the Perl stack
discipline and other such arcana. XS comes to the rescue here: instead of writing this glue C code in long-
hand, one can write a more concise short-hand description of what should be done by the glue, and let the XS
compiler xsubpp handle the rest.
The XS language allows one to describe the mapping between how the C routine is used, and how the
corresponding Perl routine is used. It also allows creation of Perl routines which are directly translated to
C code and which are not related to a pre-existing C function. In cases when the C interface coincides with
the Perl interface, the XSUB declaration is almost identical to a declaration of a C function (in K&R style).
In such circumstances, there is another tool called "h2xs" that is able to translate an entire C header file
into a corresponding XS file that will provide glue to the functions/macros described in the header file.
The XS compiler is called xsubpp. This compiler creates the constructs necessary to let an XSUB manipulate
Perl values, and creates the glue necessary to let Perl call the XSUB. The compiler uses typemaps to
determine how to map C function parameters and output values to Perl values and back. The default typemap
(which comes with Perl) handles many common C types. A supplementary typemap may also be needed to handle any
special structures and types for the library being linked. For more information on typemaps, see
perlxstypemap.
A file in XS format starts with a C language section which goes until the first "MODULE =" 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. xsubpp recognizes and skips POD (see perlpod) in both the C and XS
language sections, which allows the XS file to contain embedded documentation.
See 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 <http://www.swig.org/> for more information.
time_t timep;
status = rpcb_gettime( "localhost", &timep );
If an XSUB is created to offer a direct translation between this function and Perl, then this XSUB will be
used from Perl with the following code. The $status and $timep variables will contain the output of the
function.
use RPC;
$status = rpcb_gettime( "localhost", $timep );
The following XS file shows an XS subroutine, or XSUB, which demonstrates one possible interface to the
rpcb_gettime() function. This XSUB represents a direct translation between C and Perl and so preserves the
interface even from Perl. This XSUB will be invoked from Perl with the usage shown above. Note that the
first three #include statements, for "EXTERN.h", "perl.h", and "XSUB.h", will always be present at the
beginning of an XS file. This approach and others will be expanded later in this document.
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include <rpc/rpc.h>
MODULE = RPC PACKAGE = RPC
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep
OUTPUT:
timep
Any extension to Perl, including those containing XSUBs, should have a Perl module to serve as the bootstrap
which pulls the extension into Perl. This module will export the extension's functions and variables to the
Perl program and will cause the extension's XSUBs to be linked into Perl. The following module will be used
for most of the examples in this document and should be used from Perl with the "use" command as shown
earlier. Perl modules are explained in more detail later in this document.
package RPC;
require Exporter;
require DynaLoader;
@ISA = qw(Exporter DynaLoader);
@EXPORT = qw( rpcb_gettime );
bootstrap RPC;
1;
Throughout this document a variety of interfaces to the rpcb_gettime() XSUB will be explored. The XSUBs will
take their parameters in different orders or will take different numbers of parameters. In each case the XSUB
is an abstraction between Perl and the real C rpcb_gettime() function, and the XSUB must always ensure that
the real rpcb_gettime() function is called with the correct parameters. This abstraction will allow the
programmer to create a more Perl-like interface to the C function.
The Anatomy of an XSUB
The simplest XSUBs consist of 3 parts: a description of the return value, the name of the XSUB routine and the
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);
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 xsubpp like
this:
char * s
char &c
Both these XS declarations correspond to the "char*" C type, but they have different semantics, see "The &
Unary Operator".
It is convenient to think that the indirection operator "*" should be considered as a part of the type and the
address operator "&" should be considered part of the variable. See perlxstypemap 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.
INCORRECT CORRECT
double sin(x) double
double x sin(x)
double x
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
double
sin(x)
double x
More complicated XSUBs may contain many other sections. Each section of an XSUB starts with the corresponding
keyword, such as INIT: or CLEANUP:. However, the first two lines of an XSUB always contain the same data:
descriptions of the return type and the names of the function and its parameters. Whatever immediately
follows these is considered to be an INPUT: section unless explicitly marked with another keyword. (See "The
INPUT: Keyword".)
An XSUB section continues until another section-start keyword is found.
The Argument Stack
The Perl argument stack is used to store the values which are sent as parameters to the XSUB and to store the
XSUB's return value(s). In reality all Perl functions (including non-XSUB ones) keep their values on this
matches the return type of the C library function. The xsubpp compiler will declare this variable in each
XSUB with non-"void" return type. By default the generated C function will use RETVAL to hold the return
value of the C library function being called. In simple cases the value of RETVAL will be placed in ST(0) of
the argument stack where it can be received by Perl as the return value of the XSUB.
If the XSUB has a return type of "void" then the compiler will not declare a RETVAL variable for that
function. When using a PPCODE: section no manipulation of the RETVAL variable is required, the section may
use direct stack manipulation to place output values on the stack.
If PPCODE: directive is not used, "void" return value should be used only for subroutines which do not return
a value, even if CODE: directive is used which sets ST(0) explicitly.
Older versions of this document recommended to use "void" return value in such cases. It was discovered that
this could lead to segfaults in cases when XSUB was truly "void". This practice is now deprecated, and may be
not supported at some future version. Use the return value "SV *" in such cases. (Currently "xsubpp" contains
some heuristic code which tries to disambiguate between "truly-void" and "old-practice-declared-as-void"
functions. Hence your code is at mercy of this heuristics unless you use "SV *" as return value.)
Returning SVs, AVs and HVs through RETVAL
When you're using RETVAL to return an "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 perlguts.) To make your life
easier, the typemap file automatically makes "RETVAL" mortal when you're returning an "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 "SV *", it's
unfortunately not as easy to have "AV *" or "HV *" as a return value. You 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 "AV *" is not properly decremented. Thus, the above XSUB would leak memory whenever it
is being called. The same problem exists for "HV *", "CV *", and "SVREF" (which indicates a scalar reference,
not a general "SV *"). In XS code on perls starting with perl 5.16, you can override the typemaps for any of
/* do something with RETVAL */
OUTPUT:
RETVAL
Remember that you don't have to do this for an "SV *". The reference documentation for all core typemaps can
be found in perlxstypemap.
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
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.
MODULE = RPC
The PACKAGE Keyword
When functions within an XS source file must be separated into packages the PACKAGE keyword should be used.
This keyword is used with the MODULE keyword and must follow immediately after it when used.
MODULE = RPC PACKAGE = RPC
[ XS code in package RPC ]
MODULE = RPC PACKAGE = RPCB
[ XS code in package RPCB ]
MODULE = RPC PACKAGE = 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.
The PREFIX Keyword
The PREFIX keyword designates prefixes which should be removed from the Perl function names. If the C
function is "rpcb_gettime()" and the PREFIX value is "rpcb_" then Perl will see this function as "gettime()".
This keyword should follow the PACKAGE keyword when used. If PACKAGE is not used then PREFIX should follow
the MODULE keyword.
MODULE = RPC PREFIX = rpc_
MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_
The OUTPUT: Keyword
The OUTPUT: keyword indicates that certain function parameters should be updated (new values made visible to
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep
OUTPUT:
timep
The OUTPUT: keyword will also allow an output parameter to be mapped to a matching piece of code rather than
to a typemap.
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep
OUTPUT:
timep sv_setnv(ST(1), (double)timep);
xsubpp emits an automatic "SvSETMAGIC()" for all parameters in the OUTPUT section of the XSUB, except RETVAL.
This is the usually desired behavior, as it takes care of properly invoking 'set' magic on output parameters
(needed for hash or array element parameters that must be created if they didn't exist). If for some reason,
this behavior is not desired, the OUTPUT section may contain a "SETMAGIC: DISABLE" line to disable it for the
remainder of the parameters in the OUTPUT section. Likewise, "SETMAGIC: ENABLE" can be used to reenable it
for the remainder of the OUTPUT section. See perlguts for more details about 'set' magic.
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-"void" return type, the return value of this C subroutine
should not be returned from the generated Perl subroutine.
With this keyword present "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 "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.
The CODE: Keyword
This keyword is used in more complicated XSUBs which require special handling for the C function. The RETVAL
variable is still declared, but it will not be returned unless it is specified in the OUTPUT: section.
The following XSUB is for a C function which requires special handling of its parameters. The Perl usage is
given first.
$status = rpcb_gettime( "localhost", $timep );
The INIT: Keyword
The INIT: keyword allows initialization to be inserted into the XSUB before the compiler generates the call to
the C function. Unlike the CODE: keyword above, this keyword does not affect the way the compiler handles
RETVAL.
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep
INIT:
printf("# Host is %s\n", host );
OUTPUT:
timep
Another use for the INIT: section is to check for preconditions before making a call to the C function:
long long
lldiv(a,b)
long long a
long long b
INIT:
if (a == 0 && b == 0)
XSRETURN_UNDEF;
if (b == 0)
croak("lldiv: cannot divide by 0");
The NO_INIT Keyword
The NO_INIT keyword is used to indicate that a function parameter is being used only as an output value. The
xsubpp compiler will normally generate code to read the values of all function parameters from the argument
stack and assign them to C variables upon entry to the function. NO_INIT will tell the compiler that some
parameters will be used for output rather than for input and that they will be handled before the function
terminates.
The following example shows a variation of the rpcb_gettime() function. This function uses the timep variable
only as an output variable and does not care about its initial contents.
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep = NO_INIT
OUTPUT:
timep
The TYPEMAP: Keyword
Starting with Perl 5.16, you can embed typemaps into your XS code instead of or in addition to typemaps in a
separate file. Multiple such embedded typemaps will be processed in order of appearance in the XS code and
like local typemap files take precendence over the default typemap, the embedded typemaps may overwrite
previous definitions of TYPEMAP, INPUT, and OUTPUT stanzas. The syntax for embedded typemaps is
TYPEMAP: <<HERE
... your typemap code here ...
HERE
The following code demonstrates how to supply initialization code for function parameters. The initialization
code is eval'ed within double quotes by the compiler before it is added to the output so anything which should
be interpreted literally [mainly "$", "@", or "\\"] must be protected with backslashes. The variables $var,
$arg, and $type can be used as in typemaps.
bool_t
rpcb_gettime(host,timep)
char *host = (char *)SvPV_nolen($arg);
time_t &timep = 0;
OUTPUT:
timep
This should not be used to supply default values for parameters. One would normally use this when a function
parameter must be processed by another library function before it can be used. Default parameters are covered
in the next section.
If the initialization begins with "=", then it is output in the declaration for the input variable, replacing
the initialization supplied by the typemap. If the initialization begins with ";" or "+", then it is
performed after all of the input variables have been declared. In the ";" case the initialization normally
supplied by the typemap is not performed. For the "+" case, the declaration for the variable will include the
initialization from the typemap. A global variable, %v, is available for the truly rare case where
information from one initialization is needed in another initialization.
Here's a truly obscure example:
bool_t
rpcb_gettime(host,timep)
time_t &timep; /* \$v{timep}=@{[$v{timep}=$arg]} */
char *host + SvOK($v{timep}) ? SvPV_nolen($arg) : NULL;
OUTPUT:
timep
The construct "\$v{timep}=@{[$v{timep}=$arg]}" used in the above example has a two-fold purpose: first, when
this line is processed by xsubpp, the Perl snippet "$v{timep}=$arg" is evaluated. Second, the text of the
evaluated snippet is output into the generated C file (inside a C comment)! During the processing of "char
*host" line, $arg will evaluate to ST(0), and $v{timep} will evaluate to ST(1).
Default Parameter Values
Default values for XSUB arguments can be specified by placing an assignment statement in the parameter list.
The default value may be a number, a string or the special string "NO_INIT". Defaults should always be used
on the right-most parameters only.
To allow the XSUB for rpcb_gettime() to have a default host value the parameters to the XSUB could be
rearranged. The XSUB will then call the real rpcb_gettime() function with the parameters in the correct
order. This XSUB can be called from Perl with either of the following statements:
$status = rpcb_gettime( $timep, $host );
$status = rpcb_gettime( $timep );
The XSUB will look like the code which follows. A CODE: block is used to call the real rpcb_gettime()
function with the parameters in the correct order for that function.
bool_t
If a variable is declared inside a CODE: section it will follow any typemap code that is emitted for the input
parameters. This may result in the declaration ending up after C code, which is C syntax error. Similar
errors may happen with an explicit ";"-type or "+"-type initialization of parameters is used (see
"Initializing Function Parameters"). Declaring these variables in an INIT: section will not help.
In such cases, to force an additional variable to be declared together with declarations of other variables,
place the declaration into a PREINIT: section. The PREINIT: keyword may be used one or more times within an
XSUB.
The following examples are equivalent, but if the code is using complex typemaps then the first example is
safer.
bool_t
rpcb_gettime(timep)
time_t timep = NO_INIT
PREINIT:
char *host = "localhost";
CODE:
RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
timep
RETVAL
For this particular case an INIT: keyword would generate the same C code as the PREINIT: keyword. Another
correct, but error-prone example:
bool_t
rpcb_gettime(timep)
time_t timep = NO_INIT
CODE:
char *host = "localhost";
RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
timep
RETVAL
Another way to declare "host" is to use a C block in the CODE: section:
bool_t
rpcb_gettime(timep)
time_t timep = NO_INIT
CODE:
{
char *host = "localhost";
RETVAL = rpcb_gettime( host, &timep );
}
OUTPUT:
timep
RETVAL
The ability to put additional declarations before the typemap entries are processed is very handy in the cases
when typemap conversions manipulate some global state:
There is another way to trade clarity for compactness: INPUT sections allow declaration of C variables which
do not appear in the parameter list of a subroutine. Thus the above code for mutate() can be rewritten as
MyObject
mutate(o)
MyState st = global_state;
MyObject o;
CLEANUP:
reset_to(global_state, st);
and the code for rpcb_gettime() can be rewritten as
bool_t
rpcb_gettime(timep)
time_t timep = NO_INIT
char *host = "localhost";
C_ARGS:
host, &timep
OUTPUT:
timep
RETVAL
The SCOPE: Keyword
The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If enabled, the XSUB will invoke ENTER
and LEAVE automatically.
To support potentially complex type mappings, if a typemap entry used by an XSUB contains a comment like
"/*scope*/" then scoping will be automatically enabled for that XSUB.
To enable scoping:
SCOPE: ENABLE
To disable scoping:
SCOPE: DISABLE
The INPUT: Keyword
The XSUB's parameters are usually evaluated immediately after entering the XSUB. The INPUT: keyword can be
used to force those parameters to be evaluated a little later. The INPUT: keyword can be used multiple times
within an XSUB and can be used to list one or more input variables. This keyword is used with the PREINIT:
keyword.
The following example shows how the input parameter "timep" can be evaluated late, after a PREINIT.
bool_t
rpcb_gettime(host,timep)
char *host
PREINIT:
time_t tt;
INPUT:
time_t timep
CODE:
INPUT:
char *host
PREINIT:
char *h;
INPUT:
time_t timep
CODE:
h = host;
RETVAL = rpcb_gettime( h, &tt );
timep = tt;
OUTPUT:
timep
RETVAL
Since INPUT sections allow declaration of C variables which do not appear in the parameter list of a
subroutine, this may be shortened to:
bool_t
rpcb_gettime(host,timep)
time_t tt;
char *host;
char *h = host;
time_t timep;
CODE:
RETVAL = rpcb_gettime( h, &tt );
timep = tt;
OUTPUT:
timep
RETVAL
(We used our knowledge that input conversion for "char *" is a "simple" one, thus "host" is initialized on the
declaration line, and our assignment "h = host" is not performed too early. Otherwise one would need to have
the assignment "h = host" in a CODE: or INIT: section.)
The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords
In the list of parameters for an XSUB, one can precede parameter names by the
"IN"/"OUTLIST"/"IN_OUTLIST"/"OUT"/"IN_OUT" keywords. "IN" keyword is the default, the other keywords indicate
how the Perl interface should differ from the C interface.
Parameters preceded by "OUTLIST"/"IN_OUTLIST"/"OUT"/"IN_OUT" keywords are considered to be used by the C
subroutine via pointers. "OUTLIST"/"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 "OUTLIST" keyword do not appear in the usage signature of the generated Perl function.
Parameters preceded by "IN_OUTLIST"/"IN_OUT"/"OUT" do appear as parameters to the Perl function. With the
exception of "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 "void" return type or "The NO_OUTPUT Keyword" was used) followed by all the "OUTLIST" and
"IN_OUTLIST" parameters (in the order of appearance). On the return from the XSUB the "IN_OUT"/"OUT" Perl
parameter will be modified to have the values written by the C function.
The C signature of the corresponding function should be
void day_month(int *day, int unix_time, int *month);
The "IN"/"OUTLIST"/"IN_OUTLIST"/"IN_OUT"/"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 "IN" keyword is omitted).
The "IN_OUT" parameters are identical with parameters introduced with "The & Unary Operator" and put into the
"OUTPUT:" section (see "The OUTPUT: Keyword"). The "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 "OUTLIST"/"OUT" parameter differ from "IN_OUTLIST"/"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);
The "length(NAME)" Keyword
If one of the input arguments to the C function is the length of a string argument "NAME", one can substitute
the name of the length-argument by "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++;
}
}
XSUBs. By using this mechanism one can create an XSUB which accepts a list of parameters of unknown length.
The host parameter for the rpcb_gettime() XSUB can be optional so the ellipsis can be used to indicate that
the XSUB will take a variable number of parameters. Perl should be able to call this XSUB with either of the
following statements.
$status = rpcb_gettime( $timep, $host );
$status = rpcb_gettime( $timep );
The XS code, with ellipsis, follows.
bool_t
rpcb_gettime(timep, ...)
time_t timep = NO_INIT
PREINIT:
char *host = "localhost";
CODE:
if( items > 1 )
host = (char *)SvPV_nolen(ST(1));
RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
timep
RETVAL
The C_ARGS: Keyword
The C_ARGS: keyword allows creating of XSUBS which have different calling sequence from Perl than from C,
without a need to write CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is put as the
argument to the called C function without any change.
For example, suppose that a C function is declared as
symbolic nth_derivative(int n, symbolic function, int flags);
and that the default flags are kept in a global C variable "default_flags". Suppose that you want to create
an interface which is called as
$second_deriv = $function->nth_derivative(2);
To do this, declare the XSUB as
symbolic
nth_derivative(function, n)
symbolic function
int n
C_ARGS:
n, function, default_flags
The PPCODE: Keyword
The PPCODE: keyword is an alternate form of the CODE: keyword and is used to tell the xsubpp compiler that the
programmer is supplying the code to control the argument stack for the XSUBs return values. Occasionally one
will want an XSUB to return a list of values rather than a single value. In these cases one must use PPCODE:
and then explicitly push the list of values on the stack. The PPCODE: and CODE: keywords should not be used
together within the same XSUB.
Note that macros ST(i), "XST_m*()" and "XSRETURN*()" work equally well in CODE: sections and PPCODE: sections.
The following XSUB will call the C rpcb_gettime() function and will return its two output values, timep and
status, to Perl as a single list.
void
rpcb_gettime(host)
char *host
PREINIT:
time_t timep;
bool_t status;
PPCODE:
status = rpcb_gettime( host, &timep );
EXTEND(SP, 2);
PUSHs(sv_2mortal(newSViv(status)));
PUSHs(sv_2mortal(newSViv(timep)));
Notice that the programmer must supply the C code necessary to have the real rpcb_gettime() function called
and to have the return values properly placed on the argument stack.
The "void" return type for this function tells the xsubpp compiler that the RETVAL variable is not needed or
used and that it should not be created. In most scenarios the void return type should be used with the
PPCODE: directive.
The EXTEND() macro is used to make room on the argument stack for 2 return values. The PPCODE: directive
causes the xsubpp compiler to create a stack pointer available as "SP", and it is this pointer which is being
used in the EXTEND() macro. The values are then pushed onto the stack with the PUSHs() macro.
Now the rpcb_gettime() function can be used from Perl with the following statement.
($status, $timep) = rpcb_gettime("localhost");
When handling output parameters with a PPCODE section, be sure to handle 'set' magic properly. See perlguts
for details about 'set' magic.
Returning Undef And Empty Lists
Occasionally the programmer will want to return simply "undef" or an empty list if a function fails rather
than a separate status value. The rpcb_gettime() function offers just this situation. If the function
succeeds we would like to have it return the time and if it fails we would like to have undef returned. In
the following Perl code the value of $timep will either be undef or it will be a valid time.
$timep = rpcb_gettime( "localhost" );
The following XSUB uses the "SV *" return type as a mnemonic only, and uses a CODE: block to indicate to the
compiler that the programmer has supplied all the necessary code. The sv_newmortal() call will initialize the
return value to undef, making that the default return value.
SV *
rpcb_gettime(host)
char * host
PREINIT:
time_t timep;
bool_t x;
time_t timep;
bool_t x;
CODE:
if( rpcb_gettime( host, &timep ) ){
ST(0) = sv_newmortal();
sv_setnv( ST(0), (double)timep);
}
else{
ST(0) = &PL_sv_undef;
}
To return an empty list one must use a PPCODE: block and then not push return values on the stack.
void
rpcb_gettime(host)
char *host
PREINIT:
time_t timep;
PPCODE:
if( rpcb_gettime( host, &timep ) )
PUSHs(sv_2mortal(newSViv(timep)));
else{
/* Nothing pushed on stack, so an empty
* list is implicitly returned. */
}
Some people may be inclined to include an explicit "return" in the above XSUB, rather than letting control
fall through to the end. In those situations "XSRETURN_EMPTY" should be used, instead. This will ensure that
the XSUB stack is properly adjusted. Consult perlapi for other "XSRETURN" macros.
Since "XSRETURN_*" macros can be used with CODE blocks as well, one can rewrite this example as:
int
rpcb_gettime(host)
char *host
PREINIT:
time_t timep;
CODE:
RETVAL = rpcb_gettime( host, &timep );
if (RETVAL == 0)
XSRETURN_UNDEF;
OUTPUT:
RETVAL
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;
POSTCALL:
if (RETVAL == 0)
XSRETURN_UNDEF;
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 "The NO_OUTPUT Keyword" and "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.
The BOOT: Keyword
The BOOT: keyword is used to add code to the extension's bootstrap function. The bootstrap function is
generated by the xsubpp compiler and normally holds the statements necessary to register any XSUBs with Perl.
With the BOOT: keyword the programmer can tell the compiler to add extra statements to the bootstrap function.
This keyword may be used any time after the first MODULE keyword and should appear on a line by itself. The
first blank line after the keyword will terminate the code block.
BOOT:
# The following message will be printed when the
# bootstrap function executes.
printf("Hello from the bootstrap!\n");
The VERSIONCHECK: Keyword
The VERSIONCHECK: keyword corresponds to xsubpp's "-versioncheck" and "-noversioncheck" options. This keyword
overrides the command line options. Version checking is enabled by default. When version checking is enabled
the XS module will attempt to verify that its version matches the version of the PM module.
To enable version checking:
VERSIONCHECK: ENABLE
To disable version checking:
VERSIONCHECK: DISABLE
Note that if the version of the PM module is an NV (a floating point number), it will be stringified with a
possible loss of precision (currently chopping to nine decimal places) so that it may not match the version of
the XS module anymore. Quoting the $VERSION declaration to make it a string is recommended if long version
numbers are used.
The PROTOTYPES: Keyword
The PROTOTYPES: keyword corresponds to xsubpp's "-prototypes" and "-noprototypes" options. This keyword
overrides the command line options. Prototypes are enabled by default. When prototypes are enabled XSUBs
will be given Perl prototypes. This keyword may be used multiple times in an XS module to enable and disable
prototypes for different parts of the module.
To enable prototypes:
PROTOTYPES: ENABLE
To disable prototypes:
char *host = "localhost";
CODE:
if( items > 1 )
host = (char *)SvPV_nolen(ST(1));
RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
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
...
The ALIAS: Keyword
The ALIAS: keyword allows an XSUB to have two or more unique Perl names and to know which of those names was
used when it was invoked. The Perl names may be fully-qualified with package names. Each alias is given an
index. The compiler will setup a variable called "ix" which contain the index of the alias which was used.
When the XSUB is called with its declared name "ix" will be 0.
The following example will create aliases "FOO::gettime()" and "BAR::getit()" for this function.
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep
ALIAS:
FOO::gettime = 1
BAR::getit = 2
INIT:
printf("# ix = %d\n", ix );
OUTPUT:
timep
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
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 "fallback" in overload for more details.
The INTERFACE: Keyword
This keyword declares the current XSUB as a keeper of the given calling signature. If some text follows this
keyword, it is considered as a list of functions which have this signature, and should be attached to the
current XSUB.
For example, if you have 4 C functions multiply(), divide(), add(), subtract() all having the signature:
symbolic f(symbolic, symbolic);
you can make them all to use the same XSUB using this:
symbolic
interface_s_ss(arg1, arg2)
symbolic arg1
symbolic arg2
INTERFACE:
multiply divide
add subtract
(This is the complete XSUB code for 4 Perl functions!) Four generated Perl function share names with
corresponding C functions.
The advantage of this approach comparing to ALIAS: keyword is that there is no need to code a switch
statement, each Perl function (which shares the same XSUB) knows which C function it should call.
Additionally, one can attach an extra function remainder() at runtime by using
CV *mycv = newXSproto("Symbolic::remainder",
XS_Symbolic_interface_s_ss, __FILE__, "$$");
XSINTERFACE_FUNC_SET(mycv, remainder);
say, from another XSUB. (This example supposes that there was no INTERFACE_MACRO: section, otherwise one
needs to use something else instead of "XSINTERFACE_FUNC_SET", see the next section.)
The INTERFACE_MACRO: Keyword
This keyword allows one to define an INTERFACE using a different way to extract a function pointer from an
XSUB. The text which follows this keyword should give the name of macros which would extract/set a function
pointer. The extractor macro is given return type, "CV*", and "XSANY.any_dptr" for this "CV*". The setter
macro is given cv, and the function pointer.
The default value is "XSINTERFACE_FUNC" and "XSINTERFACE_FUNC_SET". An INTERFACE keyword with an empty list
of functions can be omitted if INTERFACE_MACRO keyword is used.
Suppose that in the previous example functions pointers for multiply(), divide(), add(), subtract() are kept
in a global C array "fp[]" with offsets being "multiply_off", "divide_off", "add_off", "subtract_off". Then
one can use
XSINTERFACE_FUNC_BYOFFSET
XSINTERFACE_FUNC_BYOFFSET_set
INTERFACE:
multiply divide
add subtract
in XSUB section.
The INCLUDE: Keyword
This keyword can be used to pull other files into the XS module. The other files may have XS code. INCLUDE:
can also be used to run a command to generate the XS code to be pulled into the module.
The file Rpcb1.xsh contains our "rpcb_gettime()" function:
bool_t
rpcb_gettime(host,timep)
char *host
time_t &timep
OUTPUT:
timep
The XS module can use INCLUDE: to pull that file into it.
INCLUDE: Rpcb1.xsh
If the parameters to the INCLUDE: keyword are followed by a pipe ("|") then the compiler will interpret the
parameters as a command. This feature is mildly deprecated in favour of the "INCLUDE_COMMAND:" directive, as
documented below.
INCLUDE: cat Rpcb1.xsh |
Do not use this to run perl: "INCLUDE: perl |" will run the perl that happens to be the first in your path and
not necessarily the same perl that is used to run "xsubpp". See "The INCLUDE_COMMAND: Keyword".
The INCLUDE_COMMAND: Keyword
Runs the supplied command and includes its output into the current XS document. "INCLUDE_COMMAND" assigns
special meaning to the $^X token in that it runs the same perl interpreter that is running "xsubpp":
INCLUDE_COMMAND: cat Rpcb1.xsh
INCLUDE_COMMAND: $^X -e ...
The CASE: Keyword
The CASE: keyword allows an XSUB to have multiple distinct parts with each part acting as a virtual XSUB.
CASE: is greedy and if it is used then all other XS keywords must be contained within a CASE:. This means
nothing may precede the first CASE: in the XSUB and anything following the last CASE: is included in that
case.
A CASE: might switch via a parameter of the XSUB, via the "ix" ALIAS: variable (see "The ALIAS: Keyword"), or
maybe via the "items" variable (see "Variable-length Parameter Lists"). The last CASE: becomes the default
case if it is not associated with a conditional. The following example shows CASE switched via "ix" with a
function "rpcb_gettime()" having an alias "x_gettime()". When the function is called as "rpcb_gettime()" its
parameters are the usual "(char *host, time_t *timep)", but when the function is called as "x_gettime()" its
parameters are reversed, "(time_t *timep, char *host)".
OUTPUT:
a
RETVAL
CASE:
# 'a' is host, 'b' is timep
char *a
time_t &b = NO_INIT
OUTPUT:
b
RETVAL
That function can be called with either of the following statements. Note the different argument lists.
$status = rpcb_gettime( $host, $timep );
$status = x_gettime( $timep, $host );
The EXPORT_XSUB_SYMBOLS: Keyword
The EXPORT_XSUB_SYMBOLS: keyword is likely something you will never need. In perl versions earlier than
5.16.0, this keyword does nothing. Starting with 5.16, XSUB symbols are no longer exported by default. That
is, they are "static" functions. If you include
EXPORT_XSUB_SYMBOLS: ENABLE
in your XS code, the XSUBs following this line will not be declared "static". You can later disable this with
EXPORT_XSUB_SYMBOLS: DISABLE
which, again, is the default that you should probably never change. You cannot use this keyword on versions
of perl before 5.16 to make XSUBs "static".
The & Unary Operator
The "&" unary operator in the INPUT: section is used to tell xsubpp that it should convert a Perl value
to/from C using the C type to the left of "&", but provide a pointer to this value when the C function is
called.
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 "int" or "long" but not an "int*" or "long*").
The following XSUB will generate incorrect C code. The xsubpp compiler will turn this into code which calls
"rpcb_gettime()" with parameters "(char *host, time_t timep)", but the real "rpcb_gettime()" wants the "timep"
parameter to be of type "time_t*" rather than "time_t".
bool_t
rpcb_gettime(host,timep)
char *host
time_t timep
OUTPUT:
timep
That problem is corrected by using the "&" operator. The xsubpp compiler will now turn this into code which
calls "rpcb_gettime()" correctly with parameters "(char *host, time_t *timep)". It does this by carrying the
"&" through, so the function call looks like "rpcb_gettime(host, &timep)".
"=cut" command; "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 "=". 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 "#" as the first non-whitespace of a line. Care should be taken
to avoid making the comment look like a C preprocessor directive, lest it be interpreted as such. The
simplest way to prevent this is to put whitespace in front of the "#".
If you use preprocessor directives to choose one of two versions of a function, use
#if ... version1
#else /* ... version2 */
#endif
and not
#if ... version1
#endif
#if ... version2
#endif
because otherwise xsubpp will believe that you made a duplicate definition of the function. Also, put a blank
line before the #else/#endif so it will not be seen as part of the function body.
Using XS With C++
If an XSUB name contains "::", it is considered to be a C++ method. The generated Perl function will assume
that its first argument is an object pointer. The object pointer will be stored in a variable called THIS.
The object should have been created by C++ with the new() function and should be blessed by Perl with the
sv_setref_pv() macro. The blessing of the object by Perl can be handled by a typemap. An example typemap is
shown at the end of this section.
If the return type of the XSUB includes "static", the method is considered to be a static method. It will
call the C++ function using the class::method() syntax. If the method is not static the function will be
called using the THIS->method() syntax.
The next examples will use the following C++ class.
class color {
public:
color();
~color();
int blue();
void set_blue( int );
private:
int c_blue;
};
The XSUBs for the blue() and set_blue() methods are defined with the class name but the parameter for the
object (THIS, or "self") is implicit and is not listed.
int
color::blue()
You could also write a single get/set method using an optional argument:
int
color::blue( val = NO_INIT )
int val
PROTOTYPE $;$
CODE:
if (items > 1)
THIS->set_blue( val );
RETVAL = THIS->blue();
OUTPUT:
RETVAL
If the function's name is DESTROY then the C++ "delete" function will be called and "THIS" will be given as
its parameter. The generated C++ code for
void
color::DESTROY()
will look like this:
color *THIS = ...; // Initialized as in typemap
delete THIS;
If the function's name is new then the C++ "new" function will be called to create a dynamic C++ object. The
XSUB will expect the class name, which will be kept in a variable called "CLASS", to be given as the first
argument.
color *
color::new()
The generated C++ code will call "new".
RETVAL = new color();
The following is an example of a typemap that could be used for this C++ example.
TYPEMAP
color * O_OBJECT
OUTPUT
# The Perl object is blessed into 'CLASS', which should be a
# char* having the name of the package for the blessing.
O_OBJECT
sv_setref_pv( $arg, CLASS, (void*)$var );
INPUT
O_OBJECT
if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) )
$var = ($type)SvIV((SV*)SvRV( $arg ));
else{
warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" );
Identify the C functions which use some inband info as an indication of failure. They may be 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 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, you may want to create a special
typedef to handle this situation. Put
typedef int negative_is_failure;
near the beginning of XS file, and create an OUTPUT typemap entry for "negative_is_failure" which converts
negative values to "undef", or maybe croak()s. After this the return value of type "negative_is_failure" will
create more Perl-like interface.
Identify which values are used by only the C and XSUB functions themselves, say, when a parameter to a
function should be a contents of a global variable. If Perl does not need to access the contents of the value
then it may not be necessary to provide a translation for that value from C to Perl.
Identify the pointers in the C function parameter lists and return values. Some pointers may be used to
implement input/output or output parameters, they can be handled in XS with the "&" unary operator, and,
possibly, using the NO_INIT keyword. Some others will require handling of types like "int *", and one needs
to decide what a useful Perl translation will do in such a case. When the semantic is clear, it is advisable
to put the translation into a typemap file.
Identify the structures used by the C functions. In many cases it may be helpful to use the T_PTROBJ typemap
for these structures so they can be manipulated by Perl as blessed objects. (This is handled automatically by
"h2xs -x".)
If the same C type is used in several different contexts which require different translations, "typedef"
several new types mapped to this C type, and create separate typemap entries for these new types. Use these
types in declarations of return type and parameters to XSUBs.
Perl Objects And C Structures
When dealing with C structures one should select either T_PTROBJ or T_PTRREF for the XS type. Both types are
designed to handle pointers to complex objects. The T_PTRREF type will allow the Perl object to be unblessed
while the T_PTROBJ type requires that the object be blessed. By using T_PTROBJ one can achieve a form of
type-checking because the XSUB will attempt to verify that the Perl object is of the expected type.
The following XS code shows the getnetconfigent() function which is used with ONC+ TIRPC. The
getnetconfigent() function will return a pointer to a C structure and has the C prototype shown below. The
example will demonstrate how the C pointer will become a Perl reference. Perl will consider this reference to
be a pointer to a blessed object and will attempt to call a destructor for the object. A destructor will be
provided in the XS source to free the memory used by getnetconfigent(). Destructors in XS can be created by
specifying an XSUB function whose name ends with the word DESTROY. XS destructors can be used to free memory
which may have been malloc'd by another XSUB.
struct netconfig *getnetconfigent(const char *netid);
A "typedef" will be created for "struct netconfig". The Perl object will be blessed in a class matching the
name of the C type, with the tag "Ptr" appended, and the name should not have embedded spaces if it will be a
Perl package name. The destructor will be placed in a class corresponding to the class of the object and the
PREFIX keyword will be used to trim the name to the word DESTROY as Perl will expect.
rpcb_DESTROY(netconf)
Netconfig *netconf
CODE:
printf("Now in NetconfigPtr::DESTROY\n");
free( netconf );
This example requires the following typemap entry. Consult perlxstypemap for more information about adding
new typemaps for an extension.
TYPEMAP
Netconfig * T_PTROBJ
This example will be used with the following Perl statements.
use RPC;
$netconf = getnetconfigent("udp");
When Perl destroys the object referenced by $netconf it will send the object to the supplied XSUB DESTROY
function. Perl cannot determine, and does not care, that this object is a C struct and not a Perl object. In
this sense, there is no difference between the object created by the getnetconfigent() XSUB and an object
created by a normal Perl subroutine.
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 "-g" ("--global") option with h2xs
(see 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:
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]);
void
CLONE(...)
CODE:
MY_CXT_CLONE;
REFERENCE
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
typedef my_cxt_t
This struct typedef must always be called "my_cxt_t". The other "CXT*" macros assume the existence of the
"my_cxt_t" typedef name.
Declare a typedef named "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;
START_MY_CXT
Always place the START_MY_CXT macro directly after the declaration of "my_cxt_t".
MY_CXT_INIT
The MY_CXT_INIT macro initialises storage for the "my_cxt_t" struct.
It must be called exactly once, typically in a BOOT: section. If you are maintaining multiple
then use this to access the "index" member
dMY_CXT;
MY_CXT.index = 2;
aMY_CXT/pMY_CXT
"dMY_CXT" may be quite expensive to calculate, and to avoid the overhead of invoking it in each function
it is possible to pass the declaration onto other functions using the "aMY_CXT"/"pMY_CXT" macros, eg
void sub1() {
dMY_CXT;
MY_CXT.index = 1;
sub2(aMY_CXT);
}
void sub2(pMY_CXT) {
MY_CXT.index = 2;
}
Analogously to "pTHX", there are equivalent forms for when the macro is the first or last in multiple
arguments, where an underscore represents a comma, i.e. "_aMY_CXT", "aMY_CXT_", "_pMY_CXT" and
"pMY_CXT_".
MY_CXT_CLONE
By default, when a new interpreter is created as a copy of an existing one (eg via "threads->create()"),
both interpreters share the same physical my_cxt_t structure. Calling "MY_CXT_CLONE" (typically via the
package's "CLONE()" function), causes a byte-for-byte copy of the structure to be taken, and any future
dMY_CXT will cause the copy to be accessed instead.
MY_CXT_INIT_INTERP(my_perl)
dMY_CXT_INTERP(my_perl)
These are versions of the macros which take an explicit interpreter as an argument.
Note that these macros will only work together within the same source file; that is, a dMY_CTX in one source
file will access a different structure than a dMY_CTX in another source file.
Thread-aware system interfaces
Starting from Perl 5.8, in C/C++ level Perl knows how to wrap system/library interfaces that have thread-aware
versions (e.g. getpwent_r()) into frontend macros (e.g. getpwent()) that correctly handle the multithreaded
interaction with the Perl interpreter. This will happen transparently, the only thing you need to do is to
instantiate a Perl interpreter.
This wrapping happens always when compiling Perl core source (PERL_CORE is defined) or the Perl core
extensions (PERL_EXT is defined). When compiling XS code outside of Perl core the wrapping does not take
place. Note, however, that intermixing the _r-forms (as Perl compiled for multithreaded operation will do)
and the _r-less forms is neither well-defined (inconsistent results, data corruption, or even crashes become
more likely), nor is it very portable.
EXAMPLES
File "RPC.xs": Interface to some ONC+ RPC bind library functions.
#include "EXTERN.h"
#include "perl.h"
time_t timep;
CODE:
ST(0) = sv_newmortal();
if( rpcb_gettime( host, &timep ) )
sv_setnv( ST(0), (double)timep );
Netconfig *
getnetconfigent(netid="udp")
char *netid
MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_
void
rpcb_DESTROY(netconf)
Netconfig *netconf
CODE:
printf("NetconfigPtr::DESTROY\n");
free( netconf );
File "typemap": Custom typemap for RPC.xs. (cf. perlxstypemap)
TYPEMAP
Netconfig * T_PTROBJ
File "RPC.pm": Perl module for the RPC extension.
package RPC;
require Exporter;
require DynaLoader;
@ISA = qw(Exporter DynaLoader);
@EXPORT = qw(rpcb_gettime getnetconfigent);
bootstrap RPC;
1;
File "rpctest.pl": Perl test program for the RPC extension.
use RPC;
$netconf = getnetconfigent();
$a = rpcb_gettime();
print "time = $a\n";
print "netconf = $netconf\n";
$netconf = getnetconfigent("tcp");
$a = rpcb_gettime("poplar");
print "time = $a\n";
print "netconf = $netconf\n";
XS VERSION
This document covers features supported by "ExtUtils::ParseXS" (also known as "xsubpp") 3.13_01.
AUTHOR
Back to main site | Back to man page index