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Man Page for PERLAPINAME
perlapi - Perl 5 application programming interface for C
extensions
DESCRIPTION
Introduction
XS is a language used to create an extension interface
between Perl and some C library which one wishes to use with
Perl. The XS interface is combined with the library to
create a new library which can be linked to Perl. An XSUB
is a function in the XS language and is the core component
of the Perl application interface.
The XS compiler is called xsubpp. This compiler will embed
the constructs necessary to let an XSUB, which is really a C
function in disguise, manipulate Perl values and creates the
glue necessary to let Perl access the XSUB. The compiler
uses typemaps to determine how to map C function parameters
and variables to Perl values. The default typemap handles
many common C types. A supplement typemap must be created
to handle special structures and types for the library being
linked.
Many of the examples which follow will concentrate on
creating an interface between Perl and the ONC+RPC bind
library functions. Specifically, the rpcb_gettime()
function will be used to demonstrate many features of the XS
language. This function has two parameters; the first is an
input parameter and the second is an output parameter. The
function also returns a status value.
bool_t rpcb_gettime(const char *host, time_t
*timep);
From C this function will be called with the following
statements.
#include <rpc/rpc.h>
bool_t status;
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 following XSUB allows a Perl program to access a C
library function called sin(). The XSUB will imitate the
C function which takes a single argument and returns a
single value.
double
sin(x)
double<tab>x
The compiler expects a tab between the parameter name and
its type, and any or no whitespace before the type. When
using C pointers the indirection operator * should be
considered part of the type and the address operator &
should be considered part of the variable, as is
demonstrated in the rpcb_gettime() function above. See the
section on typemaps for more about handling qualifiers and
unary operators in C types.
The parameter list of a function must not have whitespace
after the open-parenthesis or before the close-parenthesis.
INCORRECT CORRECT
double double
sin( x ) sin(x)
double x double x
The function name and the return type must be placed on
separate lines.
INCORRECT CORRECT
double sin(x) double
double x sin(x)
double x
The Argument Stack
The argument stack is used to store the values which are
sent as parameters to the XSUB and to store the XSUB's
return value. In reality all Perl functions keep their
values on this stack at the same time, each limited to its
own range of positions on the stack. In this document the
first position on that stack which belongs to the active
function will be referred to as position 0 for that
function.
XSUBs refer to their stack arguments with the macro ST(x),
where x refers to a position in this XSUB's part of the
stack. Position 0 for that function would be known to the
XSUB as ST(0). The XSUB's incoming parameters and outgoing
return values always begin at ST(0). For many simple cases
the xsubpp compiler will generate the code necessary to
handle the argument stack by embedding code fragments found
in the typemaps. In more complex cases the programmer must
supply the code.
The RETVAL Variable
The RETVAL variable is a magic variable which always matches
the return type of the C library function. The xsubpp
compiler will supply this variable in each XSUB and by
default will use it 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 supply a RETVAL variable for that function. When using
the PPCODE: directive the RETVAL variable may not be needed.
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 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 ]
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
Perl) when the XSUB terminates or that certain values should
be returned to the calling Perl function. For simple
functions, such as the sin() function above, the RETVAL
variable is automatically designated as an output value. In
more complex functions the xsubpp compiler will need help to
determine which variables are output variables.
This keyword will normally be used to complement the CODE:
keyword. The RETVAL variable is not recognized as an output
variable when the CODE: keyword is present. The OUTPUT:
keyword is used in this situation to tell the compiler that
RETVAL really is an output variable.
The OUTPUT: keyword can also be used to indicate that
function parameters are output variables. This may be
necessary when a parameter has been modified within the
function and the programmer would like the update to be seen
by Perl. If function parameters are listed under OUTPUT:
along with the RETVAL variable then the RETVAL variable must
be the last one listed.
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<tab>sv_setnv(ST(1), (double)timep);
The CODE: Keyword
This keyword is used in more complicated XSUBs which require
special handling for the C function. The RETVAL variable is
available but will not be returned unless it is specified
under the OUTPUT: keyword.
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 XSUB follows.
bool_t rpcb_gettime(host,timep)
char * host
time_t timep
CODE:
RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
timep
RETVAL
In many of the examples shown here the CODE: block (and
other blocks) will often be contained within braces ( { and
} ). This protects the CODE: block from complex INPUT
typemaps and ensures the resulting C code is legal.
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
Initializing Function Parameters
Function parameters are normally initialized with their
values from the argument stack. The typemaps contain the
code segments which are used to transfer the Perl values to
the C parameters. The programmer, however, is allowed to
override the typemaps and supply alternate initialization
code.
The following code demonstrates how to supply initialization
code for function parameters. The initialization code is
eval'd by the compiler before it is added to the output so
anything which should be interpreted literally, such as
double quotes, must be protected with backslashes.
bool_t
rpcb_gettime(host,timep)
char * host = (char *)SvPV(ST(0),na);
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.
Default Parameter Values
Default values can be specified for function parameters by
placing an assignment statement in the parameter list. The
default value may be a number or a string. 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. Perl will call this
XSUB 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
rpcb_gettime(timep,host="localhost")
char * host
time_t timep = NO_INIT
CODE:
RETVAL = rpcb_gettime( host, &timep );
OUTPUT:
timep
RETVAL
Variable-length Parameter Lists
XSUBs can have variable-length parameter lists by specifying
an ellipsis (...) in the parameter list. This use of the
ellipsis is similar to that found in ANSI C. The programmer
is able to determine the number of arguments passed to the
XSUB by examining the items variable which the xsubpp
compiler supplies for all 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
statments.
$status = rpcb_gettime( $timep, $host );
$status = rpcb_gettime( $timep );
The XS code, with ellipsis, follows.
bool_t
rpcb_gettime(timep, ...)
time_t timep = NO_INIT
CODE:
{
char *host = "localhost";
if( items > 1 )
host = (char *)SvPV(ST(1), na);
RETVAL = rpcb_gettime( host, &timep );
}
OUTPUT:
timep
RETVAL
The PPCODE: Keyword
The PPCODE: keyword is an alternate form of the CODE:
keyword and is used to tell the xsubpp compiler that the
programmer is supplying the code to control the argument
stack for the XSUBs return values. Occassionally one will
want an XSUB to return a list of values rather than a single
value. In these cases one must use PPCODE: and then
explicitly push the list of values on the stack. The
PPCODE: and CODE: keywords are not used together within the
same XSUB.
The following XSUB will call the C rpcb_gettime() function
and will return its two output values, timep and status, to
Perl as a single list.
void rpcb_gettime(host)
char * host
PPCODE:
{
time_t timep;
bool_t status;
status = rpcb_gettime( host, &timep );
EXTEND(sp, 2);
PUSHs(sv_2mortal(newSVnv(status)));
PUSHs(sv_2mortal(newSVnv(timep)));
}
Notice that the programmer must supply the C code necessary
to have the real rpcb_gettime() function called and to have
the return values properly placed on the argument stack.
The void return type for this function tells the xsubpp
compiler that the RETVAL variable is not needed or used and
that it should not be created. In most scenarios the void
return type should be used with the PPCODE: directive.
The EXTEND() macro is used to make room on the argument
stack for 2 return values. The PPCODE: directive causes the
xsubpp compiler to create a stack pointer called sp, and it
is this pointer which is being used in the EXTEND() macro.
The values are then pushed onto the stack with the PUSHs()
macro.
Now the rpcb_gettime() function can be used from Perl with
the following statement.
($status, $timep) = rpcb_gettime("localhost");
Returning Undef And Empty Lists
Occassionally the programmer will want to simply return
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 void return type to disable the
generation of the RETVAL variable 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.
void
rpcb_gettime(host)
char * host
CODE:
{
time_t timep;
bool_t x;
ST(0) = sv_newmortal();
if( rpcb_gettime( host, &timep ) )
sv_setnv( ST(0), (double)timep);
}
The next example demonstrates how one would place an
explicit undef in the return value, should the need arise.
void
rpcb_gettime(host)
char * host
CODE:
{
time_t timep;
bool_t x;
ST(0) = sv_newmortal();
if( rpcb_gettime( host, &timep ) ){
sv_setnv( ST(0), (double)timep);
}
else{
ST(0) = &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
PPCODE:
{
time_t timep;
if( rpcb_gettime( host, &timep ) )
PUSHs(sv_2mortal(newSVnv(timep)));
else{
/* Nothing pushed on stack, so an empty */
/* list is implicitly returned. */
}
}
The CLEANUP: Keyword
This keyword can be used when an XSUB requires special
cleanup procedures before it terminates. When the CLEANUP:
keyword is used it must follow any CODE:, PPCODE:, or
OUTPUT: blocks which are present in the XSUB. The code
specified for the cleanup block will be added as the last
statements in the XSUB.
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!0);
Inserting Comments and C Preprocessor Directives
Comments and C preprocessor directives are allowed within
CODE:, PPCODE:, BOOT:, and CLEANUP: blocks. The compiler
will pass the preprocessor directives through untouched and
will remove the commented lines. Comments can be added to
XSUBs by placing a # at the beginning of the line. Care
should be taken to avoid making the comment look like a C
preprocessor directive, lest it be interpreted as such.
Using XS With C++
If a function is defined as a C++ method then it will assume
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_setptrobj() macro. The
blessing of the object by Perl can be handled by the
T_PTROBJ typemap.
If the method is defined as static 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.
Perl Variables
The following demonstrates how the Perl variable $host can
be accessed from an XSUB. The function perl_get_sv() is
used to obtain a pointer to the variable, known as an SV
(Scalar Variable) internally. The package name RPC will be
added to the name of the variable so perl_get_sv() will know
in which package $host can be found. If the package name is
not supplied then perl_get_sv() will search package main for
the variable. The macro SvPVX() is then used to dereference
the SV to obtain a char* pointer to its contents.
void
rpcb_gettime()
PPCODE:
{
char *host;
SV *hostsv;
time_t timep;
hostsv = perl_get_sv( "RPC::host", FALSE );
if( hostsv != NULL ){
host = SvPVX( hostsv );
if( rpcb_gettime( host, &timep ) )
PUSHs(sv_2mortal(newSVnv(timep)));
}
}
This Perl code can be used to call that XSUB.
$RPC::host = "localhost";
$timep = rpcb_gettime();
In the above example the SV contained a C char* but a Perl
scalar variable may also contain numbers and references. If
the SV is expected to have a C int then the macro SvIVX()
should be used to dereference the SV. When the SV contains
a C double then SvNVX() should be used.
The macro SvRV() can be used to dereference an SV when it is
a Perl reference. The result will be another SV which
points to the actual Perl variable. This can then be
dereferenced with SvPVX(), SvNVX(), or SvIVX(). The
following XSUB will use SvRV().
void rpcb_gettime()
PPCODE:
{
char *host;
SV *rv;
SV *hostsv;
time_t timep;
rv = perl_get_sv( "RPC::host", FALSE );
if( rv != NULL ){
hostsv = SvRV( rv );
host = SvPVX( hostsv );
if( rpcb_gettime( host, &timep ) )
PUSHs(sv_2mortal(newSVnv(timep)));
}
}
This Perl code will create a variable $RPC::host which is a
reference to $MY::host. The variable $MY::host contains the
hostname which will be used.
$MY::host = "localhost";
$RPC::host = Y::host;
$timep = rpcb_gettime();
The second argument to perl_get_sv() will normally be FALSE
as shown in the above examples. An argument of TRUE will
cause variables to be created if they do not already exist.
One should not use TRUE unless steps are taken to deal with
a possibly empty SV.
XSUBs may use perl_get_av(), perl_get_hv(), and
perl_get_cv() to access Perl arrays, hashes, and code
values.
Interface Stategy
When designing an interface between Perl and a C library a
straight translation from C to XS is often sufficient. The
interface will often be very C-like and occasionally
nonintuitive, especially when the C function modifies one of
its parameters. In cases where the programmer wishes to
create a more Perl-like interface the following strategy may
help to identify the more critical parts of the interface.
Identify the C functions which modify their parameters. The
XSUBs for these functions may be able to return lists to
Perl, or may be candidates to return undef or an empty list
in case of failure.
Identify which values are used only by the C and XSUB
functions themselves. 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 can be handled in XS with the
& unary operator on the variable name while others will
require the use of the * operator on the type name. In
general it is easier to work with the & operator.
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.
The Perl Module
The Perl module is the link between the extension library,
which was generated from XS code, and the Perl interpreter.
The module is used to tell Perl what the extension library
contains. The name and package of the module should match
the name of the library.
The following is a Perl module for an extension containing
some ONC+ RPC bind library functions.
package RPC;
require Exporter;
require DynaLoader;
@ISA = qw(Exporter DynaLoader);
@EXPORT = qw( rpcb_gettime rpcb_getmaps rpcb_getaddr
rpcb_rmtcall rpcb_set rpcb_unset );
bootstrap RPC;
1;
The RPC extension contains the functions found in the
@EXPORT list. By using the Exporter module the RPC module
can make these function names visible to the rest of the
Perl program. The DynaLoader module will allow the RPC
module to bootstrap the extension library. To load this
extension and make the functions available, the following
Perl statement should be used.
use RPC;
For more information about the DynaLoader consult its
documentation in the ext/DynaLoader directory in the Perl
source.
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
since 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.
typedef struct netconfig Netconfig;
MODULE = RPC PACKAGE = RPC
Netconfig *
getnetconfigent(netid)
char * netid
MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_
void
rpcb_DESTROY(netconf)
Netconfig * netconf
CODE:
printf("Now in NetconfigPtr::DESTROY0);
free( netconf );
This example requires the following typemap entry. Consult
the typemap section 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.
C Headers and Perl
The h2xs compiler is designed to convert C header files in
/usr/include into Perl extensions. This compiler will
create a directory under the ext directory of the Perl
source and will populate it with a Makefile, a Perl Module,
an XS source file, and a MANIFEST file.
The following command will create an extension called Rusers
from the <rpcsvc/rusers.h> header.
h2xs rpcsvc/rusers
When the Rusers extension has been compiled and installed
Perl can use it to retrieve any #define statements which
were in the C header.
use Rusers;
print "RPC program number for rusers service: ";
print &RUSERSPROG, "0;
Creating A New Extension
The h2xs compiler can generate template source files and
Makefiles. These templates offer a suitable starting point
for most extensions. The following example demonstrates how
one might use h2xs to create an extension containing the RPC
functions in this document.
The extension will not use autoloaded functions and will not
define constants, so the -A option will be given to h2xs.
When run from the Perl source directory, the h2xs compiler
will create the directory ext/RPC and will populate it with
files called RPC.xs, RPC.pm, Makefile.PL, and MANIFEST. The
XS code for the RPC functions should be added to the RPC.xs
file. The @EXPORT list in RPC.pm should be updated to
include the functions from RPC.xs.
h2xs -An RPC
To compile the extension for dynamic loading the following
command should be executed from the ext/RPC directory.
make dynamic
If the extension will be statically linked into the Perl
binary then the makefile (use makefile, not Makefile) in the
Perl source directory should be edited to add ext/RPC/RPC.a
to the static_ext variable. Before making this change Perl
should have already been built. After the makefile has been
updated the following command should be executed from the
Perl source directory.
make
Perl's Configure script can also be used to add extensions.
The extension should be placed in the ext directory under
the Perl source before Perl has been built and prior to
running Configure. When Configure is run it will find the
extension along with the other extensions in the ext
directory and will add it to the list of extensions to be
built. When make is run the extension will be built along
with the other extensions.
Configure recognizes extensions if they have an XS source
file which matches the name of the extension directory. If
the extension directory includes a MANIFEST file Configure
will search that file for any .SH files and extract them
after it extracts all the other .SH files listed in the main
MANIFEST. The main Perl Makefile will then run make in the
extension's directory if it finds an XS file matching the
name of the extension's directory.
The Typemap
The typemap is a collection of code fragments which are used
by the xsubpp compiler to map C function parameters and
values to Perl values. The typemap file may consist of
three sections labeled TYPEMAP, INPUT, and OUTPUT. The
INPUT section tells the compiler how to translate Perl
values into variables of certain C types. The OUTPUT
section tells the compiler how to translate the values from
certain C types into values Perl can understand. The
TYPEMAP section tells the compiler which of the INPUT and
OUTPUT code fragments should be used to map a given C type
to a Perl value. Each of the sections of the typemap must
be preceded by one of the TYPEMAP, INPUT, or OUTPUT
keywords.
The default typemap in the 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
typemap. The xsubpp compiler will allow the extension's own
typemap to override any mappings which are in the default
typemap.
Most extensions which require a custom typemap will need
only the TYPEMAP section of the typemap file. The custom
typemap used in the getnetconfigent() example shown earlier
demonstrates what may be the typical use of extension
typemaps. That typemap is used to equate a C structure with
the T_PTROBJ typemap. The typemap used by getnetconfigent()
is shown here. Note that the C type is separated from the
XS type with a tab and that the C unary operator * is
considered to be a part of the C type name.
TYPEMAP
Netconfig *<tab>T_PTROBJ
EXAMPLES
File RPC.xs: Interface to some ONC+ RPC bind library
functions.
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include <rpc/rpc.h>
typedef struct netconfig Netconfig;
MODULE = RPC PACKAGE = RPC
void
rpcb_gettime(host="localhost")
char * host
CODE:
{
time_t timep;
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::DESTROY0);
free( netconf );
File typemap: Custom typemap for RPC.xs.
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 = $a0;
print "netconf = $netconf0;
$netconf = getnetconfigent("tcp");
$a = rpcb_gettime("poplar");
print "time = $a0;
print "netconf = $netconf0;
AUTHOR
Dean Roehrich <> September 27, 1994
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