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Man Page for PERLAPI

     perlapi - Perl 5 application programming interface for C


     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

     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

     From C this function will be called with the following

          #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>


               char *  host
               time_t  &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;

     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.


     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

     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.


          [ XS code in package RPC ]


          [ XS code in package RPCB ]


          [ 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

     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

          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.

               char *  host
               time_t  &timep

     The OUTPUT: keyword will also allow an output parameter to
     be mapped to a matching piece of code rather than to a

               char *  host
               time_t  &timep
               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

          $status = rpcb_gettime( "localhost", $timep );

     The XSUB follows.

         bool_t rpcb_gettime(host,timep)
               char *  host
               time_t  timep
                    RETVAL = rpcb_gettime( host, &timep );

     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.

               char *  host
               time_t  &timep = NO_INIT

     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

     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.

               char *  host = (char *)SvPV(ST(0),na);
               time_t  &timep = 0;

     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.

               char *  host
               time_t  timep = NO_INIT
                    RETVAL = rpcb_gettime( host, &timep );

     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

          $status = rpcb_gettime( $timep, $host );

          $status = rpcb_gettime( $timep );

     The XS code, with ellipsis, follows.

          rpcb_gettime(timep, ...)
               time_t  timep = NO_INIT
               char *host = "localhost";

               if( items > 1 )
                    host = (char *)SvPV(ST(1), na);
               RETVAL = rpcb_gettime( host, &timep );

     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
               time_t  timep;
               bool_t  status;
               status = rpcb_gettime( host, &timep );
               EXTEND(sp, 2);

     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()

     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.

               char *  host
               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.

               char *  host
               time_t  timep;
               bool_t x;
               ST(0) = sv_newmortal();
               if( rpcb_gettime( host, &timep ) ){
                    sv_setnv( ST(0), (double)timep);
                    ST(0) = &sv_undef;

     To return an empty list one must use a PPCODE: block and
     then not push return values on the stack.

               char *  host
               time_t  timep;
               if( rpcb_gettime( host, &timep ) )
               /* 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.

          # 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.

               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 ) )

     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()
               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 ) )

     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

     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;

     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

     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;


          Netconfig *
               char *  netid

          MODULE = RPC  PACKAGE = NetconfigPtr  PREFIX = rpcb_

               Netconfig *  netconf
               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.

          Netconfig *  T_PTROBJ

     This example will be used with the following Perl

          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.


     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

     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

     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.

          Netconfig *<tab>T_PTROBJ

     File RPC.xs: Interface to some ONC+ RPC bind library

          #include "EXTERN.h"
          #include "perl.h"
          #include "XSUB.h"

          #include <rpc/rpc.h>

          typedef struct netconfig Netconfig;


               char *  host
               time_t  timep;
               ST(0) = sv_newmortal();
               if( rpcb_gettime( host, &timep ) )
                    sv_setnv( ST(0), (double)timep );

          Netconfig *
               char *  netid

          MODULE = RPC  PACKAGE = NetconfigPtr  PREFIX = rpcb_

               Netconfig *  netconf
               free( netconf );

     File typemap: Custom typemap for RPC.xs.

          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;

     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;

     Dean Roehrich <> September 27, 1994



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