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-=head1 NAME
-
-perlxs - XS language reference manual
-
-=head1 DESCRIPTION
-
-=head2 Introduction
-
-XS is an interface description file format used to create an extension
-interface between Perl and C code (or a C library) which one wishes
-to use with Perl. The XS interface is combined with the library to
-create a new library which can then be either dynamically loaded
-or statically linked into perl. The XS interface description is
-written in the XS language and is the core component of the Perl
-extension interface.
-
-An B<XSUB> forms the basic unit of the XS interface. After compilation
-by the B<xsubpp> compiler, each XSUB amounts to a C function definition
-which will provide the glue between Perl calling conventions and C
-calling conventions.
-
-The glue code pulls the arguments from the Perl stack, converts these
-Perl values to the formats expected by a C function, call this C function,
-transfers the return values of the C function back to Perl.
-Return values here may be a conventional C return value or any C
-function arguments that may serve as output parameters. These return
-values may be passed back to Perl either by putting them on the
-Perl stack, or by modifying the arguments supplied from the Perl side.
-
-The above is a somewhat simplified view of what really happens. Since
-Perl allows more flexible calling conventions than C, XSUBs may do much
-more in practice, such as checking input parameters for validity,
-throwing exceptions (or returning undef/empty list) if the return value
-from the C function indicates failure, calling different C functions
-based on numbers and types of the arguments, providing an object-oriented
-interface, etc.
-
-Of course, one could write such glue code directly in C. However, this
-would be a tedious task, especially if one needs to write glue for
-multiple C functions, and/or one is not familiar enough with the Perl
-stack discipline and other such arcana. XS comes to the rescue here:
-instead of writing this glue C code in long-hand, one can write
-a more concise short-hand I<description> of what should be done by
-the glue, and let the XS compiler B<xsubpp> handle the rest.
-
-The XS language allows one to describe the mapping between how the C
-routine is used, and how the corresponding Perl routine is used. It
-also allows creation of Perl routines which are directly translated to
-C code and which are not related to a pre-existing C function. In cases
-when the C interface coincides with the Perl interface, the XSUB
-declaration is almost identical to a declaration of a C function (in K&R
-style). In such circumstances, there is another tool called C<h2xs>
-that is able to translate an entire C header file into a corresponding
-XS file that will provide glue to the functions/macros described in
-the header file.
-
-The XS compiler is called B<xsubpp>. This compiler creates
-the constructs necessary to let an XSUB manipulate Perl values, and
-creates the glue necessary to let Perl call the XSUB. The compiler
-uses B<typemaps> to determine how to map C function parameters
-and output values to Perl values and back. The default typemap
-(which comes with Perl) handles many common C types. A supplementary
-typemap may also be needed to handle any special structures and types
-for the library being linked. For more information on typemaps,
-see L<perlxstypemap>.
-
-A file in XS format starts with a C language section which goes until the
-first C<MODULE =Z<>> directive. Other XS directives and XSUB definitions
-may follow this line. The "language" used in this part of the file
-is usually referred to as the XS language. B<xsubpp> recognizes and
-skips POD (see L<perlpod>) in both the C and XS language sections, which
-allows the XS file to contain embedded documentation.
-
-See L<perlxstut> for a tutorial on the whole extension creation process.
-
-Note: For some extensions, Dave Beazley's SWIG system may provide a
-significantly more convenient mechanism for creating the extension
-glue code. See L<http://www.swig.org/> 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 simplest XSUBs consist of 3 parts: a description of the return
-value, the name of the XSUB routine and the names of its arguments,
-and a description of types or formats of the arguments.
-
-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
-
-Optionally, one can merge the description of types and the list of
-argument names, rewriting this as
-
- double
- sin(double x)
-
-This makes this XSUB look similar to an ANSI C declaration. An optional
-semicolon is allowed after the argument list, as in
-
- double
- sin(double x);
-
-Parameters with C pointer types can have different semantic: C functions
-with similar declarations
-
- bool string_looks_as_a_number(char *s);
- bool make_char_uppercase(char *c);
-
-are used in absolutely incompatible manner. Parameters to these functions
-could be described B<xsubpp> like this:
-
- char * s
- char &c
-
-Both these XS declarations correspond to the C<char*> C type, but they have
-different semantics, see L<"The & Unary Operator">.
-
-It is convenient to think that the indirection operator
-C<*> should be considered as a part of the type and the address operator C<&>
-should be considered part of the variable. See L<perlxstypemap>
-for more info about handling qualifiers and unary operators in C types.
-
-The function name and the return type must be placed on
-separate lines and should be flush left-adjusted.
-
- INCORRECT CORRECT
-
- double sin(x) double
- double x sin(x)
- double x
-
-The rest of the function description may be indented or left-adjusted. The
-following example shows a function with its body left-adjusted. Most
-examples in this document will indent the body for better readability.
-
- CORRECT
-
- double
- sin(x)
- double x
-
-More complicated XSUBs may contain many other sections. Each section of
-an XSUB starts with the corresponding keyword, such as INIT: or CLEANUP:.
-However, the first two lines of an XSUB always contain the same data:
-descriptions of the return type and the names of the function and its
-parameters. Whatever immediately follows these is considered to be
-an INPUT: section unless explicitly marked with another keyword.
-(See L<The INPUT: Keyword>.)
-
-An XSUB section continues until another section-start keyword is found.
-
-=head2 The Argument Stack
-
-The Perl argument stack is used to store the values which are
-sent as parameters to the XSUB and to store the XSUB's
-return value(s). In reality all Perl functions (including non-XSUB
-ones) keep their values on this stack all 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 special C variable that is declared automatically
-for you. The C type of RETVAL matches the return type of the C library
-function. The B<xsubpp> compiler will declare this variable in each XSUB
-with non-C<void> return type. By default the generated C function
-will use RETVAL to hold the return value of the C library function being
-called. In simple cases the value of RETVAL will be placed in ST(0) of
-the argument stack where it can be received by Perl as the return value
-of the XSUB.
-
-If the XSUB has a return type of C<void> then the compiler will
-not declare a RETVAL variable for that function. When using
-a PPCODE: section no manipulation of the RETVAL variable is required, the
-section may use direct stack manipulation to place output values on the stack.
-
-If PPCODE: directive is not used, 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<truly> 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 "truly-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 Returning SVs, AVs and HVs through RETVAL
-
-When you're using RETVAL to return an C<SV *>, there's some magic
-going on behind the scenes that should be mentioned. When you're
-manipulating the argument stack using the ST(x) macro, for example,
-you usually have to pay special attention to reference counts. (For
-more about reference counts, see L<perlguts>.) To make your life
-easier, the typemap file automatically makes C<RETVAL> mortal when
-you're returning an C<SV *>. Thus, the following two XSUBs are more
-or less equivalent:
-
- void
- alpha()
- PPCODE:
- ST(0) = newSVpv("Hello World",0);
- sv_2mortal(ST(0));
- XSRETURN(1);
-
- SV *
- beta()
- CODE:
- RETVAL = newSVpv("Hello World",0);
- OUTPUT:
- RETVAL
-
-This is quite useful as it usually improves readability. While
-this works fine for an C<SV *>, it's unfortunately not as easy
-to have C<AV *> or C<HV *> as a return value. You I<should> be
-able to write:
-
- AV *
- array()
- CODE:
- RETVAL = newAV();
- /* do something with RETVAL */
- OUTPUT:
- RETVAL
-
-But due to an unfixable bug (fixing it would break lots of existing
-CPAN modules) in the typemap file, the reference count of the C<AV *>
-is not properly decremented. Thus, the above XSUB would leak memory
-whenever it is being called. The same problem exists for C<HV *>,
-C<CV *>, and C<SVREF> (which indicates a scalar reference, not
-a general C<SV *>).
-In XS code on perls starting with perl 5.16, you can override the
-typemaps for any of these types with a version that has proper
-handling of refcounts. In your C<TYPEMAP> section, do
-
- AV* T_AVREF_REFCOUNT_FIXED
-
-to get the repaired variant. For backward compatibility with older
-versions of perl, you can instead decrement the reference count
-manually when you're returning one of the aforementioned
-types using C<sv_2mortal>:
-
- AV *
- array()
- CODE:
- RETVAL = newAV();
- sv_2mortal((SV*)RETVAL);
- /* do something with RETVAL */
- OUTPUT:
- RETVAL
-
-Remember that you don't have to do this for an C<SV *>. The reference
-documentation for all core typemaps can be found in L<perlxstypemap>.
-
-=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 with
-POD stripped, but otherwise untouched. Every XS module will have a
-bootstrap function which is used to hook the XSUBs into Perl. The package
-name of this bootstrap function will match the value of the last MODULE
-statement in the XS source files. The value of MODULE should always remain
-constant within the same XS file, though this is not required.
-
-The following example will start the XS code and will place
-all functions in a package named RPC.
-
- MODULE = RPC
-
-=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 ]
-
-The same package name can be used more than once, allowing for
-non-contiguous code. This is useful if you have a stronger ordering
-principle than package names.
-
-Although this keyword is optional and in some cases provides redundant
-information it should always be used. This keyword will ensure that the
-XSUBs appear in the desired package.
-
-=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 which have no CODE: or PPCODE: section,
-such as the sin() function above, the RETVAL variable is
-automatically designated as an output value. For 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 NO_OUTPUT Keyword
-
-The NO_OUTPUT can be placed as the first token of the XSUB. This keyword
-indicates that while the C subroutine we provide an interface to has
-a non-C<void> return type, the return value of this C subroutine should not
-be returned from the generated Perl subroutine.
-
-With this keyword present L<The RETVAL Variable> is created, and in the
-generated call to the subroutine this variable is assigned to, but the value
-of this variable is not going to be used in the auto-generated code.
-
-This keyword makes sense only if C<RETVAL> is going to be accessed by the
-user-supplied code. It is especially useful to make a function interface
-more Perl-like, especially when the C return value is just an error condition
-indicator. For example,
-
- NO_OUTPUT int
- delete_file(char *name)
- POSTCALL:
- if (RETVAL != 0)
- croak("Error %d while deleting file '%s'", RETVAL, name);
-
-Here the generated XS function returns nothing on success, and will die()
-with a meaningful error message on error.
-
-=head2 The CODE: Keyword
-
-This keyword is used in more complicated XSUBs which require
-special handling for the C function. The RETVAL variable is
-still declared, but it will not be returned unless it is specified
-in the OUTPUT: section.
-
-The following XSUB is for a C function which requires special handling of
-its parameters. The Perl usage is given first.
-
- $status = rpcb_gettime( "localhost", $timep );
-
-The 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
-
-Another use for the INIT: section is to check for preconditions before
-making a call to the C function:
-
- long long
- lldiv(a,b)
- long long a
- long long b
- INIT:
- if (a == 0 && b == 0)
- XSRETURN_UNDEF;
- if (b == 0)
- croak("lldiv: cannot divide by 0");
-
-=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 The TYPEMAP: Keyword
-
-Starting with Perl 5.16, you can embed typemaps into your XS code
-instead of or in addition to typemaps in a separate file. Multiple
-such embedded typemaps will be processed in order of appearance in
-the XS code and like local typemap files take precendence over the
-default typemap, the embedded typemaps may overwrite previous
-definitions of TYPEMAP, INPUT, and OUTPUT stanzas. The syntax for
-embedded typemaps is
-
- TYPEMAP: <<HERE
- ... your typemap code here ...
- HERE
-
-where the C<TYPEMAP> keyword must appear in the first column of a
-new line.
-
-Refer to L<perlxstypemap> for details on writing typemaps.
-
-=head2 Initializing Function Parameters
-
-C function parameters are normally initialized with their values from
-the argument stack (which in turn contains the parameters that were
-passed to the XSUB from Perl). The typemaps contain the
-code segments which are used to translate the Perl values to
-the C parameters. The programmer, however, is allowed to
-override the typemaps and supply alternate (or additional)
-initialization code. Initialization code starts with the first
-C<=>, C<;> or C<+> on a line in the INPUT: section. The only
-exception happens if this C<;> terminates the line, then this C<;>
-is quietly ignored.
-
-The following code demonstrates how to supply initialization code for
-function parameters. The initialization code is eval'ed within double
-quotes by the compiler before it is added to the output so anything
-which should be interpreted literally [mainly C<$>, C<@>, or C<\\>]
-must be protected with backslashes. The variables C<$var>, C<$arg>,
-and C<$type> can be used as in typemaps.
-
- bool_t
- rpcb_gettime(host,timep)
- char *host = (char *)SvPV_nolen($arg);
- time_t &timep = 0;
- OUTPUT:
- timep
-
-This should not be used to supply default values for parameters. One
-would normally use this when a function parameter must be processed by
-another library function before it can be used. Default parameters are
-covered in the next section.
-
-If the initialization begins with C<=>, then it is output in
-the declaration for the input variable, replacing the initialization
-supplied by the typemap. If the initialization
-begins with C<;> or C<+>, then it is performed after
-all of the input variables have been declared. In the C<;>
-case the initialization normally supplied by the typemap is not performed.
-For the C<+> case, the declaration for the variable will include the
-initialization from the typemap. A global
-variable, C<%v>, is available for the truly rare case where
-information from one initialization is needed in another
-initialization.
-
-Here's a truly obscure example:
-
- bool_t
- rpcb_gettime(host,timep)
- time_t &timep; /* \$v{timep}=@{[$v{timep}=$arg]} */
- char *host + SvOK($v{timep}) ? SvPV_nolen($arg) : NULL;
- OUTPUT:
- timep
-
-The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above
-example has a two-fold purpose: first, when this line is processed by
-B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second,
-the text of the evaluated snippet is output into the generated C file
-(inside a C comment)! During the processing of C<char *host> line,
-C<$arg> will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to
-C<ST(1)>.
-
-=head2 Default Parameter Values
-
-Default values for XSUB arguments can be specified by placing an
-assignment statement in the parameter list. The default value may
-be a number, a string or the special string C<NO_INIT>. Defaults should
-always be used on the right-most parameters only.
-
-To allow the XSUB for rpcb_gettime() to have a default host
-value the parameters to the XSUB could be rearranged. The
-XSUB will then call the real rpcb_gettime() function with
-the parameters in the correct order. This XSUB can be called
-from Perl with either of the following statements:
-
- $status = rpcb_gettime( $timep, $host );
-
- $status = rpcb_gettime( $timep );
-
-The XSUB will look like the code which follows. A CODE:
-block is used to call the real rpcb_gettime() function with
-the parameters in the correct order for that function.
-
- bool_t
- 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 immediately
-before or after the declarations of the parameters from the INPUT: section
-are emitted.
-
-If a variable is declared inside a CODE: section it will follow any typemap
-code that is emitted for the input parameters. This may result in the
-declaration ending up after C code, which is C syntax error. Similar
-errors may happen with an explicit C<;>-type or C<+>-type initialization of
-parameters is used (see L<"Initializing Function Parameters">). Declaring
-these variables in an INIT: section will not help.
-
-In such cases, to force an additional variable to be declared together
-with declarations of other variables, place the declaration into a
-PREINIT: section. The PREINIT: keyword may be used one or more times
-within an XSUB.
-
-The following examples are equivalent, but if the code is using complex
-typemaps then the first example is safer.
-
- bool_t
- rpcb_gettime(timep)
- time_t timep = NO_INIT
- PREINIT:
- char *host = "localhost";
- CODE:
- RETVAL = rpcb_gettime( host, &timep );
- OUTPUT:
- timep
- RETVAL
-
-For this particular case an INIT: keyword would generate the
-same C code as the PREINIT: keyword. Another correct, but error-prone example:
-
- bool_t
- rpcb_gettime(timep)
- time_t timep = NO_INIT
- CODE:
- char *host = "localhost";
- RETVAL = rpcb_gettime( host, &timep );
- OUTPUT:
- timep
- RETVAL
-
-Another way to declare C<host> is to use a C block in the CODE: section:
-
- bool_t
- rpcb_gettime(timep)
- time_t timep = NO_INIT
- CODE:
- {
- char *host = "localhost";
- RETVAL = rpcb_gettime( host, &timep );
- }
- OUTPUT:
- timep
- RETVAL
-
-The ability to put additional declarations before the typemap entries are
-processed is very handy in the cases when typemap conversions manipulate
-some global state:
-
- MyObject
- mutate(o)
- PREINIT:
- MyState st = global_state;
- INPUT:
- MyObject o;
- CLEANUP:
- reset_to(global_state, st);
-
-Here we suppose that conversion to C<MyObject> in the INPUT: section and from
-MyObject when processing RETVAL will modify a global variable C<global_state>.
-After these conversions are performed, we restore the old value of
-C<global_state> (to avoid memory leaks, for example).
-
-There is another way to trade clarity for compactness: INPUT sections allow
-declaration of C variables which do not appear in the parameter list of
-a subroutine. Thus the above code for mutate() can be rewritten as
-
- MyObject
- mutate(o)
- MyState st = global_state;
- MyObject o;
- CLEANUP:
- reset_to(global_state, st);
-
-and the code for rpcb_gettime() can be rewritten as
-
- bool_t
- rpcb_gettime(timep)
- time_t timep = NO_INIT
- char *host = "localhost";
- C_ARGS:
- host, &timep
- OUTPUT:
- timep
- RETVAL
-
-=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 an XSUB contains a comment like C</*scope*/> then scoping will
-be automatically 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
-
-Since INPUT sections allow declaration of C variables which do not appear
-in the parameter list of a subroutine, this may be shortened to:
-
- bool_t
- rpcb_gettime(host,timep)
- time_t tt;
- char *host;
- char *h = host;
- time_t timep;
- CODE:
- RETVAL = rpcb_gettime( h, &tt );
- timep = tt;
- OUTPUT:
- timep
- RETVAL
-
-(We used our knowledge that input conversion for C<char *> is a "simple" one,
-thus C<host> is initialized on the declaration line, and our assignment
-C<h = host> is not performed too early. Otherwise one would need to have the
-assignment C<h = host> in a CODE: or INIT: section.)
-
-=head2 The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords
-
-In the list of parameters for an XSUB, one can precede parameter names
-by the C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> keywords.
-C<IN> keyword is the default, the other keywords indicate how the Perl
-interface should differ from the C interface.
-
-Parameters preceded by C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT>
-keywords are considered to be used by the C subroutine I<via
-pointers>. C<OUTLIST>/C<OUT> keywords indicate that the C subroutine
-does not inspect the memory pointed by this parameter, but will write
-through this pointer to provide additional return values.
-
-Parameters preceded by C<OUTLIST> keyword do not appear in the usage
-signature of the generated Perl function.
-
-Parameters preceded by C<IN_OUTLIST>/C<IN_OUT>/C<OUT> I<do> appear as
-parameters to the Perl function. With the exception of
-C<OUT>-parameters, these parameters are converted to the corresponding
-C type, then pointers to these data are given as arguments to the C
-function. It is expected that the C function will write through these
-pointers.
-
-The return list of the generated Perl function consists of the C return value
-from the function (unless the XSUB is of C<void> return type or
-C<The NO_OUTPUT Keyword> was used) followed by all the C<OUTLIST>
-and C<IN_OUTLIST> parameters (in the order of appearance). On the
-return from the XSUB the C<IN_OUT>/C<OUT> Perl parameter will be
-modified to have the values written by the C function.
-
-For example, an XSUB
-
- void
- day_month(OUTLIST day, IN unix_time, OUTLIST month)
- int day
- int unix_time
- int month
-
-should be used from Perl as
-
- my ($day, $month) = day_month(time);
-
-The C signature of the corresponding function should be
-
- void day_month(int *day, int unix_time, int *month);
-
-The C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<IN_OUT>/C<OUT> keywords can be
-mixed with ANSI-style declarations, as in
-
- void
- day_month(OUTLIST int day, int unix_time, OUTLIST int month)
-
-(here the optional C<IN> keyword is omitted).
-
-The C<IN_OUT> parameters are identical with parameters introduced with
-L<The & Unary Operator> and put into the C<OUTPUT:> section (see
-L<The OUTPUT: Keyword>). The C<IN_OUTLIST> parameters are very similar,
-the only difference being that the value C function writes through the
-pointer would not modify the Perl parameter, but is put in the output
-list.
-
-The C<OUTLIST>/C<OUT> parameter differ from C<IN_OUTLIST>/C<IN_OUT>
-parameters only by the initial value of the Perl parameter not
-being read (and not being given to the C function - which gets some
-garbage instead). For example, the same C function as above can be
-interfaced with as
-
- void day_month(OUT int day, int unix_time, OUT int month);
-
-or
-
- void
- day_month(day, unix_time, month)
- int &day = NO_INIT
- int unix_time
- int &month = NO_INIT
- OUTPUT:
- day
- month
-
-However, the generated Perl function is called in very C-ish style:
-
- my ($day, $month);
- day_month($day, time, $month);
-
-=head2 The C<length(NAME)> Keyword
-
-If one of the input arguments to the C function is the length of a string
-argument C<NAME>, one can substitute the name of the length-argument by
-C<length(NAME)> in the XSUB declaration. This argument must be omitted when
-the generated Perl function is called. E.g.,
-
- void
- dump_chars(char *s, short l)
- {
- short n = 0;
- while (n < l) {
- printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]);
- n++;
- }
- }
-
- MODULE = x PACKAGE = x
-
- void dump_chars(char *s, short length(s))
-
-should be called as C<dump_chars($string)>.
-
-This directive is supported with ANSI-type function declarations only.
-
-=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_nolen(ST(1));
- 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 PPCODE: section. The contents of the C_ARGS: paragraph is
-put as the argument to the called C function without any change.
-
-For example, suppose that a C function is declared as
-
- symbolic nth_derivative(int n, symbolic function, int flags);
-
-and that the default flags are kept in a global C variable
-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 should not be used
-together within the same XSUB.
-
-The actual difference between PPCODE: and CODE: sections is in the
-initialization of C<SP> macro (which stands for the I<current> Perl
-stack pointer), and in the handling of data on the stack when returning
-from an XSUB. In CODE: sections SP preserves the value which was on
-entry to the XSUB: SP is on the function pointer (which follows the
-last parameter). In PPCODE: sections SP is moved backward to the
-beginning of the parameter list, which allows C<PUSH*()> macros
-to place output values in the place Perl expects them to be when
-the XSUB returns back to Perl.
-
-The generated trailer for a CODE: section ensures that the number of return
-values Perl will see is either 0 or 1 (depending on the C<void>ness of the
-return value of the C function, and heuristics mentioned in
-L<"The RETVAL Variable">). The trailer generated for a PPCODE: section
-is based on the number of return values and on the number of times
-C<SP> was updated by C<[X]PUSH*()> macros.
-
-Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally
-well in CODE: sections and PPCODE: sections.
-
-The following XSUB will call the C rpcb_gettime() function
-and will return its two output values, timep and status, to
-Perl as a single list.
-
- void
- rpcb_gettime(host)
- char *host
- PREINIT:
- time_t timep;
- bool_t status;
- PPCODE:
- status = rpcb_gettime( host, &timep );
- EXTEND(SP, 2);
- PUSHs(sv_2mortal(newSViv(status)));
- PUSHs(sv_2mortal(newSViv(timep)));
-
-Notice that the programmer must supply the C code necessary
-to have the real rpcb_gettime() function called and to have
-the return values properly placed on the argument stack.
-
-The 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:
- if( rpcb_gettime( host, &timep ) ){
- ST(0) = sv_newmortal();
- sv_setnv( ST(0), (double)timep);
- }
- else{
- ST(0) = &PL_sv_undef;
- }
-
-To return an empty list one must use a PPCODE: block and
-then not push return values on the stack.
-
- void
- rpcb_gettime(host)
- char *host
- PREINIT:
- time_t timep;
- PPCODE:
- if( rpcb_gettime( host, &timep ) )
- PUSHs(sv_2mortal(newSViv(timep)));
- else{
- /* Nothing pushed on stack, so an empty
- * list is implicitly returned. */
- }
-
-Some people may be inclined to include an explicit 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<perlapi> for other
-C<XSRETURN> macros.
-
-Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can
-rewrite this example as:
-
- int
- rpcb_gettime(host)
- char *host
- PREINIT:
- time_t timep;
- CODE:
- RETVAL = rpcb_gettime( host, &timep );
- if (RETVAL == 0)
- XSRETURN_UNDEF;
- OUTPUT:
- RETVAL
-
-In fact, one can put this check into a POSTCALL: section as well. Together
-with PREINIT: simplifications, this leads to:
-
- int
- rpcb_gettime(host)
- char *host
- time_t timep;
- POSTCALL:
- if (RETVAL == 0)
- XSRETURN_UNDEF;
-
-=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 POSTCALL: Keyword
-
-This keyword can be used when an XSUB requires special procedures
-executed after the C subroutine call is performed. When the POSTCALL:
-keyword is used it must precede OUTPUT: and CLEANUP: blocks which are
-present in the XSUB.
-
-See examples in L<"The NO_OUTPUT Keyword"> and L<"Returning Undef And Empty Lists">.
-
-The POSTCALL: block does not make a lot of sense when the C subroutine
-call is supplied by user by providing either CODE: or PPCODE: section.
-
-=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
-
-Note that if the version of the PM module is an NV (a floating point
-number), it will be stringified with a possible loss of precision
-(currently chopping to nine decimal places) so that it may not match
-the version of the XS module anymore. Quoting the $VERSION declaration
-to make it a string is recommended if long version numbers are used.
-
-=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_nolen(ST(1));
- RETVAL = rpcb_gettime( host, &timep );
- OUTPUT:
- timep
- RETVAL
-
-If the prototypes are enabled, you can disable it locally for a given
-XSUB as in the following example:
-
- void
- rpcb_gettime_noproto()
- PROTOTYPE: DISABLE
- ...
-
-=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 OVERLOAD: Keyword
-
-Instead of writing an overloaded interface using pure Perl, you
-can also use the OVERLOAD keyword to define additional Perl names
-for your functions (like the ALIAS: keyword above). However, the
-overloaded functions must be defined with three parameters (except
-for the nomethod() function which needs four parameters). If any
-function has the OVERLOAD: keyword, several additional lines
-will be defined in the c file generated by xsubpp in order to
-register with the overload magic.
-
-Since blessed objects are actually stored as RV's, it is useful
-to use the typemap features to preprocess parameters and extract
-the actual SV stored within the blessed RV. See the sample for
-T_PTROBJ_SPECIAL below.
-
-To use the OVERLOAD: keyword, create an XS function which takes
-three input parameters ( or use the c style '...' definition) like
-this:
-
- SV *
- cmp (lobj, robj, swap)
- My_Module_obj lobj
- My_Module_obj robj
- IV swap
- OVERLOAD: cmp <=>
- { /* function defined here */}
-
-In this case, the function will overload both of the three way
-comparison operators. For all overload operations using non-alpha
-characters, you must type the parameter without quoting, separating
-multiple overloads with whitespace. Note that "" (the stringify
-overload) should be entered as \"\" (i.e. escaped).
-
-=head2 The FALLBACK: Keyword
-
-In addition to the OVERLOAD keyword, if you need to control how
-Perl autogenerates missing overloaded operators, you can set the
-FALLBACK keyword in the module header section, like this:
-
- MODULE = RPC PACKAGE = RPC
-
- FALLBACK: TRUE
- ...
-
-where FALLBACK can take any of the three values TRUE, FALSE, or
-UNDEF. If you do not set any FALLBACK value when using OVERLOAD,
-it defaults to UNDEF. FALLBACK is not used except when one or
-more functions using OVERLOAD have been defined. Please see
-L<overload/fallback> for more details.
-
-=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 the current XSUB.
-
-For example, if you have 4 C functions multiply(), divide(), add(),
-subtract() all having the signature:
-
- symbolic f(symbolic, symbolic);
-
-you can make them all to use the same XSUB using this:
-
- symbolic
- interface_s_ss(arg1, arg2)
- symbolic arg1
- symbolic arg2
- INTERFACE:
- multiply divide
- add subtract
-
-(This is the complete XSUB code for 4 Perl functions!) Four generated
-Perl function share names with corresponding C functions.
-
-The advantage of this approach comparing to ALIAS: keyword is that there
-is no need to code a switch statement, each Perl function (which shares
-the same XSUB) knows which C function it should call. Additionally, one
-can attach an extra function remainder() at runtime by using
-
- CV *mycv = newXSproto("Symbolic::remainder",
- XS_Symbolic_interface_s_ss, __FILE__, "$$");
- XSINTERFACE_FUNC_SET(mycv, remainder);
-
-say, from another XSUB. (This example supposes that there was no
-INTERFACE_MACRO: section, otherwise one needs to use something else instead of
-C<XSINTERFACE_FUNC_SET>, see the next section.)
-
-=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_ANON(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. This feature is
-mildly deprecated in favour of the C<INCLUDE_COMMAND:> directive, as documented
-below.
-
- INCLUDE: cat Rpcb1.xsh |
-
-Do not use this to run perl: C<INCLUDE: perl |> will run the perl that
-happens to be the first in your path and not necessarily the same perl that is
-used to run C<xsubpp>. See L<"The INCLUDE_COMMAND: Keyword">.
-
-=head2 The INCLUDE_COMMAND: Keyword
-
-Runs the supplied command and includes its output into the current XS
-document. C<INCLUDE_COMMAND> assigns special meaning to the C<$^X> token
-in that it runs the same perl interpreter that is running C<xsubpp>:
-
- INCLUDE_COMMAND: cat Rpcb1.xsh
-
- INCLUDE_COMMAND: $^X -e ...
-
-=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 EXPORT_XSUB_SYMBOLS: Keyword
-
-The EXPORT_XSUB_SYMBOLS: keyword is likely something you will never need.
-In perl versions earlier than 5.16.0, this keyword does nothing. Starting
-with 5.16, XSUB symbols are no longer exported by default. That is, they
-are C<static> functions. If you include
-
- EXPORT_XSUB_SYMBOLS: ENABLE
-
-in your XS code, the XSUBs following this line will not be declared C<static>.
-You can later disable this with
-
- EXPORT_XSUB_SYMBOLS: DISABLE
-
-which, again, is the default that you should probably never change.
-You cannot use this keyword on versions of perl before 5.16 to make
-XSUBs C<static>.
-
-=head2 The & Unary Operator
-
-The C<&> unary operator in the INPUT: section is used to tell B<xsubpp>
-that it should convert a Perl value to/from C using the C type to the left
-of C<&>, but provide a pointer to this value when the C function is called.
-
-This is useful to avoid a CODE: block for a C function which takes a parameter
-by reference. Typically, the parameter should be not a pointer type (an
-C<int> or C<long> but not an C<int*> or C<long*>).
-
-The following XSUB will generate incorrect C code. The B<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 B<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 POD, Comments and C Preprocessor Directives
-
-C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:,
-PPCODE:, POSTCALL:, 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. POD documentation is allowed at any point, both in the
-C and XS language sections. POD must be terminated with a C<=cut> command;
-C<xsubpp> will exit with an error if it does not. It is very unlikely that
-human generated C code will be mistaken for POD, as most indenting styles
-result in whitespace in front of any line starting with C<=>. Machine
-generated XS files may fall into this trap unless care is taken to
-ensure that a space breaks the sequence "\n=".
-
-Comments can be added to XSUBs by placing a 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 B<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 an XSUB name contains C<::>, it is considered to be a C++ method.
-The generated Perl function will assume that
-its first argument is an object pointer. The object pointer
-will be stored in a variable called THIS. The object should
-have been created by C++ with the new() function and should
-be blessed by Perl with the sv_setref_pv() macro. The
-blessing of the object by Perl can be handled by a typemap. An example
-typemap is shown at the end of this section.
-
-If the return type of the XSUB includes C<static>, the method is considered
-to be a static method. It will call the C++
-function using the class::method() syntax. If the method is not static
-the function will be called using the THIS-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 Perl functions will expect an object as the first parameter. In the
-generated C++ code the object is called C<THIS>, and the method call will
-be performed on this object. So in the C++ code the blue() and set_blue()
-methods will be called as this:
-
- RETVAL = THIS->blue();
-
- THIS->set_blue( val );
-
-You could also write a single get/set method using an optional argument:
-
- int
- color::blue( val = NO_INIT )
- int val
- PROTOTYPE $;$
- CODE:
- if (items > 1)
- THIS->set_blue( val );
- RETVAL = THIS->blue();
- OUTPUT:
- RETVAL
-
-If the function's name is B<DESTROY> then the C++ C<delete> function will be
-called and C<THIS> will be given as its parameter. The generated C++ code for
-
- void
- color::DESTROY()
-
-will look like this:
-
- color *THIS = ...; // Initialized as in typemap
-
- delete THIS;
-
-If the function's name is 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 generated 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 (such as created by C<h2xs -x>) is often sufficient.
-However, sometimes the interface will look
-very C-like and occasionally nonintuitive, especially when the C function
-modifies one of its parameters, or returns failure inband (as in "negative
-return values mean failure"). 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 with input/output or output parameters. The XSUBs for
-these functions may be able to return lists to Perl.
-
-Identify the C functions which use some inband info as an indication
-of failure. They may be
-candidates to return undef or an empty list in case of failure. If the
-failure may be detected without a call to the C function, you may want to use
-an INIT: section to report the failure. For failures detectable after the C
-function returns one may want to use a POSTCALL: section to process the
-failure. In more complicated cases use CODE: or PPCODE: sections.
-
-If many functions use the same failure indication based on the return value,
-you may want to create a special typedef to handle this situation. Put
-
- typedef int negative_is_failure;
-
-near the beginning of XS file, and create an OUTPUT typemap entry
-for C<negative_is_failure> which converts negative values to C<undef>, or
-maybe croak()s. After this the return value of type C<negative_is_failure>
-will create more Perl-like interface.
-
-Identify which values are used by only the C and XSUB functions
-themselves, say, when a parameter to a function should be a contents of a
-global variable. If Perl does not need to access the contents of the value
-then it may not be necessary to provide a translation for that value
-from C to Perl.
-
-Identify the pointers in the C function parameter lists and return
-values. Some pointers may be used to implement input/output or
-output parameters, they can be handled in XS with the C<&> unary operator,
-and, possibly, using the NO_INIT keyword.
-Some others will require handling of types like C<int *>, and one needs
-to decide what a useful Perl translation will do in such a case. When
-the semantic is clear, it is advisable to put the translation into a typemap
-file.
-
-Identify the structures used by the C functions. In many
-cases it may be helpful to use the T_PTROBJ typemap for
-these structures so they can be manipulated by Perl as
-blessed objects. (This is handled automatically by C<h2xs -x>.)
-
-If the same C type is used in several different contexts which require
-different translations, C<typedef> several new types mapped to this C type,
-and create separate F<typemap> entries for these new types. Use these
-types in declarations of return type and parameters to XSUBs.
-
-=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
-L<perlxstypemap> for more information about adding new typemaps
-for an extension.
-
- TYPEMAP
- Netconfig * T_PTROBJ
-
-This example will be used with the following Perl statements.
-
- use RPC;
- $netconf = getnetconfigent("udp");
-
-When Perl destroys the object referenced by $netconf it will send the
-object to the supplied XSUB DESTROY function. Perl cannot determine, and
-does not care, that this object is a C struct and not a Perl object. In
-this sense, there is no difference between the object created by the
-getnetconfigent() XSUB and an object created by a normal Perl subroutine.
-
-=head2 Safely Storing Static Data in XS
-
-Starting with Perl 5.8, a macro framework has been defined to allow
-static data to be safely stored in XS modules that will be accessed from
-a multi-threaded Perl.
-
-Although primarily designed for use with multi-threaded Perl, the macros
-have been designed so that they will work with non-threaded Perl as well.
-
-It is therefore strongly recommended that these macros be used by all
-XS modules that make use of static data.
-
-The easiest way to get a template set of macros to use is by specifying
-the C<-g> (C<--global>) option with h2xs (see L<h2xs>).
-
-Below is an example module that makes use of the macros.
-
- #include "EXTERN.h"
- #include "perl.h"
- #include "XSUB.h"
-
- /* Global Data */
-
- #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION
-
- typedef struct {
- int count;
- char name[3][100];
- } my_cxt_t;
-
- START_MY_CXT
-
- MODULE = BlindMice PACKAGE = BlindMice
-
- BOOT:
- {
- MY_CXT_INIT;
- MY_CXT.count = 0;
- strcpy(MY_CXT.name[0], "None");
- strcpy(MY_CXT.name[1], "None");
- strcpy(MY_CXT.name[2], "None");
- }
-
- int
- newMouse(char * name)
- char * name;
- PREINIT:
- dMY_CXT;
- CODE:
- if (MY_CXT.count >= 3) {
- warn("Already have 3 blind mice");
- RETVAL = 0;
- }
- else {
- RETVAL = ++ MY_CXT.count;
- strcpy(MY_CXT.name[MY_CXT.count - 1], name);
- }
-
- char *
- get_mouse_name(index)
- int index
- CODE:
- dMY_CXT;
- RETVAL = MY_CXT.lives ++;
- if (index > MY_CXT.count)
- croak("There are only 3 blind mice.");
- else
- RETVAL = newSVpv(MY_CXT.name[index - 1]);
-
- void
- CLONE(...)
- CODE:
- MY_CXT_CLONE;
-
-B<REFERENCE>
-
-=over 5
-
-=item MY_CXT_KEY
-
-This macro is used to define a unique key to refer to the static data
-for an XS module. The suggested naming scheme, as used by h2xs, is to
-use a string that consists of the module name, the string "::_guts"
-and the module version number.
-
- #define MY_CXT_KEY "MyModule::_guts" XS_VERSION
-
-=item typedef my_cxt_t
-
-This struct typedef I<must> always be called C<my_cxt_t>. The other
-C<CXT*> macros assume the existence of the C<my_cxt_t> typedef name.
-
-Declare a typedef named C<my_cxt_t> that is a structure that contains
-all the data that needs to be interpreter-local.
-
- typedef struct {
- int some_value;
- } my_cxt_t;
-
-=item START_MY_CXT
-
-Always place the START_MY_CXT macro directly after the declaration
-of C<my_cxt_t>.
-
-=item MY_CXT_INIT
-
-The MY_CXT_INIT macro initialises storage for the C<my_cxt_t> struct.
-
-It I<must> be called exactly once, typically in a BOOT: section. If you
-are maintaining multiple interpreters, it should be called once in each
-interpreter instance, except for interpreters cloned from existing ones.
-(But see L</MY_CXT_CLONE> below.)
-
-=item dMY_CXT
-
-Use the dMY_CXT macro (a declaration) in all the functions that access
-MY_CXT.
-
-=item MY_CXT
-
-Use the MY_CXT macro to access members of the C<my_cxt_t> struct. For
-example, if C<my_cxt_t> is
-
- typedef struct {
- int index;
- } my_cxt_t;
-
-then use this to access the C<index> member
-
- dMY_CXT;
- MY_CXT.index = 2;
-
-=item aMY_CXT/pMY_CXT
-
-C<dMY_CXT> may be quite expensive to calculate, and to avoid the overhead
-of invoking it in each function it is possible to pass the declaration
-onto other functions using the C<aMY_CXT>/C<pMY_CXT> macros, eg
-
- void sub1() {
- dMY_CXT;
- MY_CXT.index = 1;
- sub2(aMY_CXT);
- }
-
- void sub2(pMY_CXT) {
- MY_CXT.index = 2;
- }
-
-Analogously to C<pTHX>, there are equivalent forms for when the macro is the
-first or last in multiple arguments, where an underscore represents a
-comma, i.e. C<_aMY_CXT>, C<aMY_CXT_>, C<_pMY_CXT> and C<pMY_CXT_>.
-
-=item MY_CXT_CLONE
-
-By default, when a new interpreter is created as a copy of an existing one
-(eg via C<< threads->create() >>), both interpreters share the same physical
-my_cxt_t structure. Calling C<MY_CXT_CLONE> (typically via the package's
-C<CLONE()> function), causes a byte-for-byte copy of the structure to be
-taken, and any future dMY_CXT will cause the copy to be accessed instead.
-
-=item MY_CXT_INIT_INTERP(my_perl)
-
-=item dMY_CXT_INTERP(my_perl)
-
-These are versions of the macros which take an explicit interpreter as an
-argument.
-
-=back
-
-Note that these macros will only work together within the I<same> source
-file; that is, a dMY_CTX in one source file will access a different structure
-than a dMY_CTX in another source file.
-
-=head2 Thread-aware system interfaces
-
-Starting from Perl 5.8, in C/C++ level Perl knows how to wrap
-system/library interfaces that have thread-aware versions
-(e.g. getpwent_r()) into frontend macros (e.g. getpwent()) that
-correctly handle the multithreaded interaction with the Perl
-interpreter. This will happen transparently, the only thing
-you need to do is to instantiate a Perl interpreter.
-
-This wrapping happens always when compiling Perl core source
-(PERL_CORE is defined) or the Perl core extensions (PERL_EXT is
-defined). When compiling XS code outside of Perl core the wrapping
-does not take place. Note, however, that intermixing the _r-forms
-(as Perl compiled for multithreaded operation will do) and the _r-less
-forms is neither well-defined (inconsistent results, data corruption,
-or even crashes become more likely), nor is it very portable.
-
-=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. (cf. L<perlxstypemap>)
-
- 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<ExtUtils::ParseXS>
-(also known as C<xsubpp>) 3.13_01.
-
-=head1 AUTHOR
-
-Originally written by Dean Roehrich <F<roehrich@cray.com>>.
-
-Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>.