Initial import of Perl5. The king is dead; long live the king!

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+=head1 NAME
+
+perlxs - XS language reference manual
+
+=head1 DESCRIPTION
+
+=head2 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 B<XSUB>
+is a function in the XS language and is the core component
+of the Perl application interface.
+
+The XS compiler is called B<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 B<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.
+
+See L<perlxstut> for a tutorial on the whole extension creation process.
+
+Note: For many extensions, Dave Beazley's SWIG system provides a
+significantly more convenient mechanism for creating the XS glue
+code. See L<http://www.cs.utah.edu/~beazley/SWIG> for more 
+information.
+
+=head2 On The Road
+
+Many of the examples which follow will concentrate on creating an interface
+between Perl and the ONC+ RPC bind library functions.  The rpcb_gettime()
+function is 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
+C<EXTERN.h>, C<perl.h>, and C<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 C<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.
+
+=head2 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 x
+
+When using C pointers the indirection operator C<*> should be considered
+part of the type and the address operator C<&> 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 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 function body may be indented or left-adjusted.  The following example
+shows a function with its body left-adjusted.  Most examples in this
+document will indent the body.
+
+  CORRECT
+
+  double
+  sin(x)
+  double x
+
+=head2 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 B<ST(x)>, where I<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 B<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.
+
+=head2 The RETVAL Variable
+
+The RETVAL variable is a magic variable which always matches
+the return type of the C library function.  The B<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 C<void> then the compiler will
+not supply a RETVAL variable for that function.  When using
+the PPCODE: directive the RETVAL variable is not needed, unless used
+explicitly.
+
+If PPCODE: directive is not used, C<void> return value should be used
+only for subroutines which do not return a value, I<even if> CODE:
+directive is used which sets ST(0) explicitly.
+
+Older versions of this document recommended to use C<void> return
+value in such cases. It was discovered that this could lead to
+segfaults in cases when XSUB was I<truely> C<void>. This practice is
+now deprecated, and may be not supported at some future version. Use
+the return value C<SV *> in such cases. (Currently C<xsubpp> contains
+some heuristic code which tries to disambiguate between "truely-void"
+and "old-practice-declared-as-void" functions. Hence your code is at
+mercy of this heuristics unless you use C<SV *> as return value.)
+
+=head2 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
+
+=head2 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.
+
+=head2 The PREFIX Keyword
+
+The PREFIX keyword designates prefixes which should be
+removed from the Perl function names.  If the C function is
+C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will
+see this function as C<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_
+
+=head2 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 B<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.
+
+     bool_t
+     rpcb_gettime(host,timep)
+          char *host
+          time_t &timep
+          OUTPUT:
+          timep
+
+The OUTPUT: keyword will also allow an output parameter to
+be mapped to a matching piece of code rather than to a
+typemap.
+
+     bool_t
+     rpcb_gettime(host,timep)
+          char *host
+          time_t &timep
+          OUTPUT:
+          timep sv_setnv(ST(1), (double)timep);
+
+B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the
+OUTPUT section of the XSUB, except RETVAL.  This is the usually desired
+behavior, as it takes care of properly invoking 'set' magic on output
+parameters (needed for hash or array element parameters that must be
+created if they didn't exist).  If for some reason, this behavior is
+not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line
+to disable it for the remainder of the parameters in the OUTPUT section.
+Likewise,  C<SETMAGIC: ENABLE> can be used to reenable it for the
+remainder of the OUTPUT section.  See L<perlguts> for more details
+about 'set' magic.
+
+=head2 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
+
+=head2 The INIT: Keyword
+
+The INIT: keyword allows initialization to be inserted into the XSUB before
+the compiler generates the call to the C function.  Unlike the CODE: keyword
+above, this keyword does not affect the way the compiler handles RETVAL.
+
+    bool_t
+    rpcb_gettime(host,timep)
+          char *host
+          time_t &timep
+	  INIT:
+	  printf("# Host is %s\n", host );
+          OUTPUT:
+          timep
+
+=head2 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 B<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
+
+=head2 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 (or additional)
+initialization code.
+
+The following code demonstrates how to supply initialization code for
+function parameters.  The initialization code is eval'd within double
+quotes by the compiler before it is added to the output so anything
+which should be interpreted literally [mainly C<$>, C<@>, or C<\\>]
+must be protected with backslashes.  The variables C<$var>, C<$arg>,
+and C<$type> can be used as in typemaps.
+
+     bool_t
+     rpcb_gettime(host,timep)
+          char *host = (char *)SvPV($arg,PL_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.
+
+If the initialization begins with C<=>, then it is output on
+the same line where the input variable is declared.  If the
+initialization begins with C<;> or C<+>, then it is output after
+all of the input variables have been declared.  The C<=> and C<;>
+cases replace the initialization normally supplied from the typemap.
+For the C<+> case, the initialization from the typemap will preceed
+the initialization code included after the C<+>.  A global
+variable, C<%v>, is available for the truely rare case where
+information from one initialization is needed in another
+initialization.
+
+     bool_t
+     rpcb_gettime(host,timep)
+          time_t &timep ; /*\$v{time}=@{[$v{time}=$arg]}*/
+          char *host + SvOK($v{time}) ? SvPV($arg,PL_na) : NULL;
+          OUTPUT:
+          timep
+
+=head2 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
+
+=head2 The PREINIT: Keyword
+
+The PREINIT: keyword allows extra variables to be declared before the
+typemaps are expanded.  If a variable is declared in a CODE: block then that
+variable will follow any typemap code.  This may result in a C syntax
+error.  To force the variable to be declared before the typemap code, place
+it into a PREINIT: block.  The PREINIT: keyword may be used one or more
+times within an XSUB.
+
+The following examples are equivalent, but if the code is using complex
+typemaps then the first example is safer.
+
+     bool_t
+     rpcb_gettime(timep)
+          time_t timep = NO_INIT
+	  PREINIT:
+          char *host = "localhost";
+          CODE:
+	  RETVAL = rpcb_gettime( host, &timep );
+          OUTPUT:
+          timep
+          RETVAL
+
+A correct, but error-prone example.
+
+     bool_t
+     rpcb_gettime(timep)
+          time_t timep = NO_INIT
+	  CODE:
+          char *host = "localhost";
+	  RETVAL = rpcb_gettime( host, &timep );
+          OUTPUT:
+          timep
+          RETVAL
+
+=head2 The SCOPE: Keyword
+
+The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If
+enabled, the XSUB will invoke ENTER and LEAVE automatically.
+
+To support potentially complex type mappings, if a typemap entry used
+by this XSUB contains a comment like C</*scope*/> then scoping will
+automatically be enabled for that XSUB.
+
+To enable scoping:
+
+    SCOPE: ENABLE
+
+To disable scoping:
+
+    SCOPE: DISABLE
+
+=head2 The INPUT: Keyword
+
+The XSUB's parameters are usually evaluated immediately after entering the
+XSUB.  The INPUT: keyword can be used to force those parameters to be
+evaluated a little later.  The INPUT: keyword can be used multiple times
+within an XSUB and can be used to list one or more input variables.  This
+keyword is used with the PREINIT: keyword.
+
+The following example shows how the input parameter C<timep> can be
+evaluated late, after a PREINIT.
+
+    bool_t
+    rpcb_gettime(host,timep)
+          char *host
+	  PREINIT:
+	  time_t tt;
+	  INPUT:
+          time_t timep
+          CODE:
+               RETVAL = rpcb_gettime( host, &tt );
+	       timep = tt;
+          OUTPUT:
+          timep
+          RETVAL
+
+The next example shows each input parameter evaluated late.
+
+    bool_t
+    rpcb_gettime(host,timep)
+	  PREINIT:
+	  time_t tt;
+	  INPUT:
+          char *host
+	  PREINIT:
+	  char *h;
+	  INPUT:
+          time_t timep
+          CODE:
+	       h = host;
+	       RETVAL = rpcb_gettime( h, &tt );
+	       timep = tt;
+          OUTPUT:
+          timep
+          RETVAL
+
+=head2 Variable-length Parameter Lists
+
+XSUBs can have variable-length parameter lists by specifying an ellipsis
+C<(...)> 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 C<items> variable which the
+B<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 I<host> parameter for the rpcb_gettime() XSUB can be
+optional so the ellipsis can be used to indicate that the
+XSUB will take a variable number of parameters.  Perl should
+be able to call this XSUB with either of the following statements.
+
+     $status = rpcb_gettime( $timep, $host );
+
+     $status = rpcb_gettime( $timep );
+
+The XS code, with ellipsis, follows.
+
+     bool_t
+     rpcb_gettime(timep, ...)
+          time_t timep = NO_INIT
+	  PREINIT:
+          char *host = "localhost";
+          CODE:
+		  if( items > 1 )
+		       host = (char *)SvPV(ST(1), PL_na);
+		  RETVAL = rpcb_gettime( host, &timep );
+          OUTPUT:
+          timep
+          RETVAL
+
+=head2 The C_ARGS: Keyword
+
+The C_ARGS: keyword allows creating of XSUBS which have different
+calling sequence from Perl than from C, without a need to write
+CODE: or CPPCODE: section.  The contents of the C_ARGS: paragraph is
+put as the argument to the called C function without any change.
+
+For example, suppose that C function is declared as
+
+    symbolic nth_derivative(int n, symbolic function, int flags);
+
+and that the default flags are kept in a global C variable
+C<default_flags>.  Suppose that you want to create an interface which
+is called as
+
+    $second_deriv = $function->nth_derivative(2);
+
+To do this, declare the XSUB as
+
+    symbolic
+    nth_derivative(function, n)
+	symbolic	function
+	int		n
+    C_ARGS:
+	n, function, default_flags
+
+=head2 The PPCODE: Keyword
+
+The PPCODE: keyword is an alternate form of the CODE: keyword and is used
+to tell the B<xsubpp> compiler that the programmer is supplying the code to
+control the argument stack for the XSUBs return values.  Occasionally one
+will want an XSUB to return a list of values rather than a single value.
+In these cases one must use PPCODE: and then explicitly push the list of
+values on the stack.  The PPCODE: and CODE:  keywords are not used
+together within the same XSUB.
+
+The following XSUB will call the C rpcb_gettime() function
+and will return its two output values, timep and status, to
+Perl as a single list.
+
+     void
+     rpcb_gettime(host)
+          char *host
+	  PREINIT:
+          time_t  timep;
+          bool_t  status;
+          PPCODE:
+          status = rpcb_gettime( host, &timep );
+          EXTEND(SP, 2);
+          PUSHs(sv_2mortal(newSViv(status)));
+          PUSHs(sv_2mortal(newSViv(timep)));
+
+Notice that the programmer must supply the C code necessary
+to have the real rpcb_gettime() function called and to have
+the return values properly placed on the argument stack.
+
+The C<void> return type for this function tells the B<xsubpp> compiler that
+the RETVAL variable is not needed or used and that it should not be created.
+In most scenarios the void return type should be used with the PPCODE:
+directive.
+
+The EXTEND() macro is used to make room on the argument
+stack for 2 return values.  The PPCODE: directive causes the
+B<xsubpp> compiler to create a stack pointer available as C<SP>, and it
+is this pointer which is being used in the EXTEND() macro.
+The values are then pushed onto the stack with the PUSHs()
+macro.
+
+Now the rpcb_gettime() function can be used from Perl with
+the following statement.
+
+     ($status, $timep) = rpcb_gettime("localhost");
+
+When handling output parameters with a PPCODE section, be sure to handle
+'set' magic properly.  See L<perlguts> for details about 'set' magic.
+
+=head2 Returning Undef And Empty Lists
+
+Occasionally the programmer will want to return simply
+C<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 C<SV *> return type as a mnemonic only,
+and uses a CODE: block to indicate to the compiler
+that the programmer has supplied all the necessary code.  The
+sv_newmortal() call will initialize the return value to undef, making that
+the default return value.
+
+     SV *
+     rpcb_gettime(host)
+          char *  host
+	  PREINIT:
+          time_t  timep;
+          bool_t x;
+          CODE:
+          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.
+
+     SV *
+     rpcb_gettime(host)
+          char *  host
+	  PREINIT:
+          time_t  timep;
+          bool_t x;
+          CODE:
+          ST(0) = sv_newmortal();
+          if( rpcb_gettime( host, &timep ) ){
+               sv_setnv( ST(0), (double)timep);
+          }
+          else{
+               ST(0) = &PL_sv_undef;
+          }
+
+To return an empty list one must use a PPCODE: block and
+then not push return values on the stack.
+
+     void
+     rpcb_gettime(host)
+          char *host
+	  PREINIT:
+          time_t  timep;
+          PPCODE:
+          if( rpcb_gettime( host, &timep ) )
+               PUSHs(sv_2mortal(newSViv(timep)));
+          else{
+          /* Nothing pushed on stack, so an empty */
+          /* list is implicitly returned. */
+          }
+
+Some people may be inclined to include an explicit C<return> in the above
+XSUB, rather than letting control fall through to the end.  In those
+situations C<XSRETURN_EMPTY> should be used, instead.  This will ensure that
+the XSUB stack is properly adjusted.  Consult L<perlguts/"API LISTING"> for
+other C<XSRETURN> macros.
+
+=head2 The REQUIRE: Keyword
+
+The REQUIRE: keyword is used to indicate the minimum version of the
+B<xsubpp> compiler needed to compile the XS module.  An XS module which
+contains the following statement will compile with only B<xsubpp> version
+1.922 or greater:
+
+	REQUIRE: 1.922
+
+=head2 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.
+
+=head2 The BOOT: Keyword
+
+The BOOT: keyword is used to add code to the extension's bootstrap
+function.  The bootstrap function is generated by the B<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");
+
+=head2 The VERSIONCHECK: Keyword
+
+The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and
+C<-noversioncheck> options.  This keyword overrides the command line
+options.  Version checking is enabled by default.  When version checking is
+enabled the XS module will attempt to verify that its version matches the
+version of the PM module.
+
+To enable version checking:
+
+    VERSIONCHECK: ENABLE
+
+To disable version checking:
+
+    VERSIONCHECK: DISABLE
+
+=head2 The PROTOTYPES: Keyword
+
+The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and
+C<-noprototypes> options.  This keyword overrides the command line options.
+Prototypes are enabled by default.  When prototypes are enabled XSUBs will
+be given Perl prototypes.  This keyword may be used multiple times in an XS
+module to enable and disable prototypes for different parts of the module.
+
+To enable prototypes:
+
+    PROTOTYPES: ENABLE
+
+To disable prototypes:
+
+    PROTOTYPES: DISABLE
+
+=head2 The PROTOTYPE: Keyword
+
+This keyword is similar to the PROTOTYPES: keyword above but can be used to
+force B<xsubpp> to use a specific prototype for the XSUB.  This keyword
+overrides all other prototype options and keywords but affects only the
+current XSUB.  Consult L<perlsub/Prototypes> for information about Perl
+prototypes.
+
+    bool_t
+    rpcb_gettime(timep, ...)
+          time_t timep = NO_INIT
+	  PROTOTYPE: $;$
+	  PREINIT:
+          char *host = "localhost";
+          CODE:
+		  if( items > 1 )
+		       host = (char *)SvPV(ST(1), PL_na);
+		  RETVAL = rpcb_gettime( host, &timep );
+          OUTPUT:
+          timep
+          RETVAL
+
+=head2 The ALIAS: Keyword
+
+The ALIAS: keyword allows an XSUB to have two or more unique Perl names
+and to know which of those names was used when it was invoked.  The Perl
+names may be fully-qualified with package names.  Each alias is given an
+index.  The compiler will setup a variable called C<ix> which contain the
+index of the alias which was used.  When the XSUB is called with its
+declared name C<ix> will be 0.
+
+The following example will create aliases C<FOO::gettime()> and
+C<BAR::getit()> for this function.
+
+    bool_t
+    rpcb_gettime(host,timep)
+          char *host
+          time_t &timep
+	  ALIAS:
+	    FOO::gettime = 1
+	    BAR::getit = 2
+	  INIT:
+	  printf("# ix = %d\n", ix );
+          OUTPUT:
+          timep
+
+=head2 The INTERFACE: Keyword
+
+This keyword declares the current XSUB as a keeper of the given
+calling signature.  If some text follows this keyword, it is
+considered as a list of functions which have this signature, and
+should be attached to XSUBs.
+
+Say, if you have 4 functions multiply(), divide(), add(), subtract() all
+having the signature
+
+    symbolic f(symbolic, symbolic);
+
+you code them all by using XSUB
+
+    symbolic
+    interface_s_ss(arg1, arg2)  
+	symbolic	arg1
+	symbolic	arg2
+    INTERFACE:
+	multiply divide 
+	add subtract
+
+The advantage of this approach comparing to ALIAS: keyword is that one
+can attach an extra function remainder() at runtime by using
+    
+    CV *mycv = newXSproto("Symbolic::remainder", 
+			  XS_Symbolic_interface_s_ss, __FILE__, "$$");
+    XSINTERFACE_FUNC_SET(mycv, remainder);
+
+(This example supposes that there was no INTERFACE_MACRO: section,
+otherwise one needs to use something else instead of
+C<XSINTERFACE_FUNC_SET>.)
+
+=head2 The INTERFACE_MACRO: Keyword
+
+This keyword allows one to define an INTERFACE using a different way
+to extract a function pointer from an XSUB.  The text which follows
+this keyword should give the name of macros which would extract/set a
+function pointer.  The extractor macro is given return type, C<CV*>,
+and C<XSANY.any_dptr> for this C<CV*>.  The setter macro is given cv,
+and the function pointer.
+
+The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>.
+An INTERFACE keyword with an empty list of functions can be omitted if
+INTERFACE_MACRO keyword is used.
+
+Suppose that in the previous example functions pointers for 
+multiply(), divide(), add(), subtract() are kept in a global C array
+C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>,
+C<subtract_off>.  Then one can use 
+
+    #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \
+	((XSINTERFACE_CVT(ret,))fp[CvXSUBANY(cv).any_i32])
+    #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \
+	CvXSUBANY(cv).any_i32 = CAT2( f, _off )
+
+in C section,
+
+    symbolic
+    interface_s_ss(arg1, arg2)  
+	symbolic	arg1
+	symbolic	arg2
+    INTERFACE_MACRO: 
+	XSINTERFACE_FUNC_BYOFFSET
+	XSINTERFACE_FUNC_BYOFFSET_set
+    INTERFACE:
+	multiply divide 
+	add subtract
+
+in XSUB section.
+
+=head2 The INCLUDE: Keyword
+
+This keyword can be used to pull other files into the XS module.  The other
+files may have XS code.  INCLUDE: can also be used to run a command to
+generate the XS code to be pulled into the module.
+
+The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function:
+
+    bool_t
+    rpcb_gettime(host,timep)
+          char *host
+          time_t &timep
+          OUTPUT:
+          timep
+
+The XS module can use INCLUDE: to pull that file into it.
+
+    INCLUDE: Rpcb1.xsh
+
+If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then
+the compiler will interpret the parameters as a command.
+
+    INCLUDE: cat Rpcb1.xsh |
+
+=head2 The CASE: Keyword
+
+The CASE: keyword allows an XSUB to have multiple distinct parts with each
+part acting as a virtual XSUB.  CASE: is greedy and if it is used then all
+other XS keywords must be contained within a CASE:.  This means nothing may
+precede the first CASE: in the XSUB and anything following the last CASE: is
+included in that case.
+
+A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS:
+variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable
+(see L<"Variable-length Parameter Lists">).  The last CASE: becomes the
+B<default> case if it is not associated with a conditional.  The following
+example shows CASE switched via C<ix> with a function C<rpcb_gettime()>
+having an alias C<x_gettime()>.  When the function is called as
+C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>,
+but when the function is called as C<x_gettime()> its parameters are
+reversed, C<(time_t *timep, char *host)>.
+
+    long
+    rpcb_gettime(a,b)
+      CASE: ix == 1
+	  ALIAS:
+	  x_gettime = 1
+	  INPUT:
+	  # 'a' is timep, 'b' is host
+          char *b
+          time_t a = NO_INIT
+          CODE:
+               RETVAL = rpcb_gettime( b, &a );
+          OUTPUT:
+          a
+          RETVAL
+      CASE:
+	  # 'a' is host, 'b' is timep
+          char *a
+          time_t &b = NO_INIT
+          OUTPUT:
+          b
+          RETVAL
+
+That function can be called with either of the following statements.  Note
+the different argument lists.
+
+	$status = rpcb_gettime( $host, $timep );
+
+	$status = x_gettime( $timep, $host );
+
+=head2 The & Unary Operator
+
+The & unary operator is used to tell the compiler that it should dereference
+the object when it calls the C function.  This is used when a CODE: block is
+not used and the object is a not a pointer type (the object is an C<int> or
+C<long> but not a C<int*> or C<long*>).
+
+The following XSUB will generate incorrect C code.  The xsubpp compiler will
+turn this into code which calls C<rpcb_gettime()> with parameters C<(char
+*host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep>
+parameter to be of type C<time_t*> rather than C<time_t>.
+
+    bool_t
+    rpcb_gettime(host,timep)
+          char *host
+          time_t timep
+          OUTPUT:
+          timep
+
+That problem is corrected by using the C<&> operator.  The xsubpp compiler
+will now turn this into code which calls C<rpcb_gettime()> correctly with
+parameters C<(char *host, time_t *timep)>.  It does this by carrying the
+C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>.
+
+    bool_t
+    rpcb_gettime(host,timep)
+          char *host
+          time_t &timep
+          OUTPUT:
+          timep
+
+=head2 Inserting Comments and C Preprocessor Directives
+
+C preprocessor directives are allowed within BOOT:, PREINIT: INIT:,
+CODE:, PPCODE:, and CLEANUP: blocks, as well as outside the functions.
+Comments are allowed anywhere after the MODULE keyword.  The compiler
+will pass the preprocessor directives through untouched and will remove
+the commented lines.
+
+Comments can be added to XSUBs by placing a C<#> as the first
+non-whitespace of a line.  Care should be taken to avoid making the
+comment look like a C preprocessor directive, lest it be interpreted as
+such.  The simplest way to prevent this is to put whitespace in front of
+the C<#>.
+
+If you use preprocessor directives to choose one of two
+versions of a function, use
+
+    #if ... version1
+    #else /* ... version2  */
+    #endif
+
+and not
+
+    #if ... version1
+    #endif
+    #if ... version2
+    #endif
+
+because otherwise xsubpp will believe that you made a duplicate
+definition of the function.  Also, put a blank line before the
+#else/#endif so it will not be seen as part of the function body.
+
+=head2 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_setref_pv() macro.  The
+blessing of the object by Perl can be handled by a typemap.  An example
+typemap is shown at the end of this section.
+
+If the 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-E<gt>method() syntax.
+
+The next examples will use the following C++ class.
+
+     class color {
+          public:
+          color();
+          ~color();
+          int blue();
+          void set_blue( int );
+
+          private:
+          int c_blue;
+     };
+
+The XSUBs for the blue() and set_blue() methods are defined with the class
+name but the parameter for the object (THIS, or "self") is implicit and is
+not listed.
+
+     int
+     color::blue()
+
+     void
+     color::set_blue( val )
+          int val
+
+Both functions will expect an object as the first parameter.  The xsubpp
+compiler will call that object C<THIS> and will use it to call the specified
+method.  So in the C++ code the blue() and set_blue() methods will be called
+in the following manner.
+
+     RETVAL = THIS->blue();
+
+     THIS->set_blue( val );
+
+If the function's name is B<DESTROY> then the C++ C<delete> function will be
+called and C<THIS> will be given as its parameter.
+
+     void
+     color::DESTROY()
+
+The C++ code will call C<delete>.
+
+     delete THIS;
+
+If the function's name is B<new> then the C++ C<new> function will be called
+to create a dynamic C++ object.  The XSUB will expect the class name, which
+will be kept in a variable called C<CLASS>, to be given as the first
+argument.
+
+     color *
+     color::new()
+
+The C++ code will call C<new>.
+
+	RETVAL = new color();
+
+The following is an example of a typemap that could be used for this C++
+example.
+
+    TYPEMAP
+    color *		O_OBJECT
+
+    OUTPUT
+    # The Perl object is blessed into 'CLASS', which should be a
+    # char* having the name of the package for the blessing.
+    O_OBJECT
+    	sv_setref_pv( $arg, CLASS, (void*)$var );
+
+    INPUT
+    O_OBJECT
+    	if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) )
+    		$var = ($type)SvIV((SV*)SvRV( $arg ));
+    	else{
+    		warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" );
+    		XSRETURN_UNDEF;
+    	}
+
+=head2 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.
+
+=head2 Perl Objects And C Structures
+
+When dealing with C structures one should select either
+B<T_PTROBJ> or B<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 B<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 C<typedef> will be created for C<struct netconfig>.  The Perl
+object will be blessed in a class matching the name of the C
+type, with the tag C<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.
+
+=head2 The Typemap
+
+The typemap is a collection of code fragments which are used by the B<xsubpp>
+compiler to map C function parameters and values to Perl values.  The
+typemap file may consist of three sections labeled C<TYPEMAP>, C<INPUT>, and
+C<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 C<ext> directory of the Perl source contains many
+useful types which can be used by Perl extensions.  Some extensions define
+additional typemaps which they keep in their own directory.  These
+additional typemaps may reference INPUT and OUTPUT maps in the main
+typemap.  The B<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 C<*> is considered to be a part of the C type name.
+
+     TYPEMAP
+     Netconfig *<tab>T_PTROBJ
+
+Here's a more complicated example: suppose that you wanted C<struct
+netconfig> to be blessed into the class C<Net::Config>.  One way to do
+this is to use underscores (_) to separate package names, as follows:
+
+        typedef struct netconfig * Net_Config;
+
+And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to
+double-colons (::), and declare C<Net_Config> to be of that type:
+
+
+        TYPEMAP
+        Net_Config      T_PTROBJ_SPECIAL
+
+        INPUT
+        T_PTROBJ_SPECIAL
+                if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) {
+                        IV tmp = SvIV((SV*)SvRV($arg));
+                $var = ($type) tmp;
+                }
+                else
+                        croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")
+
+        OUTPUT
+        T_PTROBJ_SPECIAL
+                sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\",
+                (void*)$var);
+
+The INPUT and OUTPUT sections substitute underscores for double-colons
+on the fly, giving the desired effect.  This example demonstrates some
+of the power and versatility of the typemap facility.
+
+=head1 EXAMPLES
+
+File C<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
+
+     SV *
+     rpcb_gettime(host="localhost")
+          char *host
+	  PREINIT:
+          time_t  timep;
+          CODE:
+          ST(0) = sv_newmortal();
+          if( rpcb_gettime( host, &timep ) )
+               sv_setnv( ST(0), (double)timep );
+
+     Netconfig *
+     getnetconfigent(netid="udp")
+          char *netid
+
+     MODULE = RPC  PACKAGE = NetconfigPtr  PREFIX = rpcb_
+
+     void
+     rpcb_DESTROY(netconf)
+          Netconfig *netconf
+          CODE:
+          printf("NetconfigPtr::DESTROY\n");
+          free( netconf );
+
+File C<typemap>: Custom typemap for RPC.xs.
+
+     TYPEMAP
+     Netconfig *  T_PTROBJ
+
+File C<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 C<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";
+
+
+=head1 XS VERSION
+
+This document covers features supported by C<xsubpp> 1.935.
+
+=head1 AUTHOR
+
+Dean Roehrich <F<roehrich@cray.com>>
+Jul 8, 1996