PERLAPI(1)PERLAPI(1)NAMEperlapi - 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.
It is recommended that the h2xs tool be used when creating new
extensions. This tool will generate template source files and
Makefiles. This is discussed in more detail in the section titled
"Creating A New Extension" and in the h2xs manpage.
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 as only 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 as only 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 statements.
$status = rpcb_gettime( $timep, $host );
$status = rpcb_gettime( $timep );
The XS code, with ellipsis, follows.
bool_t
rpcb_gettime(timep, ...)
time_t timep = NO_INIT
CODE:
{
char *host = "localhost";
if( items > 1 )
host = (char *)SvPV(ST(1), na);
RETVAL = rpcb_gettime( host, &timep );
}
OUTPUT:
timep
RETVAL
The PPCODE: Keyword
The PPCODE: keyword is an alternate form of the CODE: keyword and is
used to tell the xsubpp compiler that the programmer is supplying the
code to control the argument stack for the XSUBs return values.
Occasionally one will want an XSUB to return a list of values rather
than a single value. In these cases one must use PPCODE: and then
explicitly push the list of values on the stack. The PPCODE: and CODE:
keywords are not used together within the same XSUB.
The following XSUB will call the C rpcb_gettime() function and will
return its two output values, timep and status, to Perl as a single
list.
void
rpcb_gettime(host)
char * host
PPCODE:
{
time_t timep;
bool_t status;
status = rpcb_gettime( host, &timep );
EXTEND(sp, 2);
PUSHs(sv_2mortal(newSVnv(status)));
PUSHs(sv_2mortal(newSVnv(timep)));
}
Notice that the programmer must supply the C code necessary to have the
real rpcb_gettime() function called and to have the return values
properly placed on the argument stack.
The void return type for this function tells the xsubpp compiler that
the RETVAL variable is not needed or used and that it should not be
created. In most scenarios the void return type should be used with
the PPCODE: directive.
The EXTEND() macro is used to make room on the argument stack for 2
return values. The PPCODE: directive causes the xsubpp compiler to
create a stack pointer called sp, and it is this pointer which is being
used in the EXTEND() macro. The values are then pushed onto the stack
with the PUSHs() macro.
Now the rpcb_gettime() function can be used from Perl with the
following statement.
($status, $timep) = rpcb_gettime("localhost");
Returning Undef And Empty Lists
Occasionally 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!\n");
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 = \$MY::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 Strategy
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 by only 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 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.
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::DESTROY\n");
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, "\n";
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::DESTROY\n");
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 = $a\n";
print "netconf = $netconf\n";
$netconf = getnetconfigent("tcp");
$a = rpcb_gettime("poplar");
print "time = $a\n";
print "netconf = $netconf\n";
AUTHOR
Dean Roehrich <roehrich@cray.com> May 3, 1995
3rd Berkeley DistributionPERLAPI(1)