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NAME

perlxs - XS language reference manual

DESCRIPTION

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 XSUB forms the basic unit of the XS interface. After compilation by the 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 description of what should be done by the glue, and let the XS compiler 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 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 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 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.

A file in XS format starts with a C language section which goes until the first MODULE = 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. xsubpp recognizes and skips POD (see perlpod) in both the C and XS language sections, which allows the XS file to contain embedded documentation.

See 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 http://www.swig.org/ for more information.

The REQUIRE: Keyword

The REQUIRE: keyword is used to indicate the minimum version of the xsubpp compiler needed to compile the XS module. An XS module which contains the following statement will compile with only xsubpp version 1.922 or greater:

 
	REQUIRE: 1.922  

The CLEANUP: Keyword

This keyword can be used when an XSUB requires special cleanup procedures before it terminates. When the CLEANUP: keyword is used it must follow any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The code specified for the cleanup block will be added as the last statements in the XSUB.

The 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 "The NO_OUTPUT Keyword" and "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.

The BOOT: Keyword

The BOOT: keyword is used to add code to the extension's bootstrap function. The bootstrap function is generated by the xsubpp compiler and normally holds the statements necessary to register any XSUBs with Perl. With the BOOT: keyword the programmer can tell the compiler to add extra statements to the bootstrap function.

This keyword may be used any time after the first MODULE keyword and should appear on a line by itself. The first blank line after the keyword will terminate the code block.

 
     BOOT:
     # The following message will be printed when the
     # bootstrap function executes.
     printf("Hello from the bootstrap!\n");  

The VERSIONCHECK: Keyword

The VERSIONCHECK: keyword corresponds to xsubpp's -versioncheck and -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  

The PROTOTYPES: Keyword

The PROTOTYPES: keyword corresponds to xsubpp's -prototypes and -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  

The PROTOTYPE: Keyword

This keyword is similar to the PROTOTYPES: keyword above but can be used to force 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 perlsub/Prototypes for information about Perl prototypes.

 
    bool_t
    rpcb_gettime(timep, ...)
          time_t timep = NO_INIT
	PROTOTYPE: $;$
	PREINIT:
          char *host = "localhost";
	  STRLEN n_a;
        CODE:
		  if( items > 1 )
		       host = (char *)SvPV(ST(1), n_a);
		  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
    ...  

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 ix which contain the index of the alias which was used. When the XSUB is called with its declared name ix will be 0.

The following example will create aliases FOO::gettime() and 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  

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, seperating multiple overloads with whitespace. Note that "" (the stringify overload) should be entered as \"\" (i.e. escaped).

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 XSINTERFACE_FUNC_SET, see the next section.)

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, CV*, and XSANY.any_dptr for this CV*. The setter macro is given cv, and the function pointer.

The default value is XSINTERFACE_FUNC and 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 fp[] with offsets being multiply_off, divide_off, add_off, 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.

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 Rpcb1.xsh contains our 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 (|) then the compiler will interpret the parameters as a command.

 
    INCLUDE: cat Rpcb1.xsh |  

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 ix ALIAS: variable (see "The ALIAS: Keyword"), or maybe via the items variable (see "Variable-length Parameter Lists"). The last CASE: becomes the default case if it is not associated with a conditional. The following example shows CASE switched via ix with a function rpcb_gettime() having an alias x_gettime(). When the function is called as rpcb_gettime() its parameters are the usual (char *host, time_t *timep), but when the function is called as x_gettime() its parameters are reversed, (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 );  

The & Unary Operator

The & unary operator in the INPUT: section is used to tell xsubpp that it should convert a Perl value to/from C using the C type to the left of &, 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 int or long but not an int* or long*).

The following XSUB will generate incorrect C code. The xsubpp compiler will turn this into code which calls rpcb_gettime() with parameters (char *host, time_t timep), but the real rpcb_gettime() wants the timep parameter to be of type time_t* rather than time_t.

 
    bool_t
    rpcb_gettime(host,timep)
          char *host
          time_t timep
        OUTPUT:
          timep  

That problem is corrected by using the & operator. The xsubpp compiler will now turn this into code which calls rpcb_gettime() correctly with parameters (char *host, time_t *timep). It does this by carrying the & through, so the function call looks like rpcb_gettime(host, &timep).

 
    bool_t
    rpcb_gettime(host,timep)
          char *host
          time_t &timep
        OUTPUT:
          timep  

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 =cut command; 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 =. 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 # 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 #.

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.

Using XS With C++

If an XSUB name contains ::, 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 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->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 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 DESTROY then the C++ delete function will be called and 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 new then the 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 CLASS, to be given as the first argument.

 
     color *
     color::new()  

The generated C++ code will call 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;
    	}  

Interface Strategy

When designing an interface between Perl and a C library a straight translation from C to XS (such as created by 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 negative_is_failure which converts negative values to undef, or maybe croak()s. After this the return value of type 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 & unary operator, and, possibly, using the NO_INIT keyword. Some others will require handling of types like 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 h2xs -x.)

If the same C type is used in several different contexts which require different translations, typedef several new types mapped to this C type, and create separate typemap entries for these new types. Use these types in declarations of return type and parameters to XSUBs.

Perl Objects And C Structures

When dealing with C structures one should select either T_PTROBJ or T_PTRREF for the XS type. Both types are designed to handle pointers to complex objects. The T_PTRREF type will allow the Perl object to be unblessed while the T_PTROBJ type requires that the object be blessed. By using T_PTROBJ one can achieve a form of type-checking because the XSUB will attempt to verify that the Perl object is of the expected type.

The following XS code shows the getnetconfigent() function which is used with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a C structure and has the C prototype shown below. The example will demonstrate how the C pointer will become a Perl reference. Perl will consider this reference to be a pointer to a blessed object and will attempt to call a destructor for the object. A destructor will be provided in the XS source to free the memory used by getnetconfigent(). Destructors in XS can be created by specifying an XSUB function whose name ends with the word DESTROY. XS destructors can be used to free memory which may have been malloc'd by another XSUB.

 
     struct netconfig *getnetconfigent(const char *netid);  

A typedef will be created for struct netconfig. The Perl object will be blessed in a class matching the name of the C type, with the tag Ptr appended, and the name should not have embedded spaces if it will be a Perl package name. The destructor will be placed in a class corresponding to the class of the object and the PREFIX keyword will be used to trim the name to the word DESTROY as Perl will expect.

 
     typedef struct netconfig Netconfig;

     MODULE = RPC  PACKAGE = RPC

     Netconfig *
     getnetconfigent(netid)
          char *netid

     MODULE = RPC  PACKAGE = NetconfigPtr  PREFIX = rpcb_

     void
     rpcb_DESTROY(netconf)
          Netconfig *netconf
        CODE:
          printf("Now in NetconfigPtr::DESTROY\n");
          free( netconf );  

This example requires the following typemap entry. Consult the typemap section for more information about adding new typemaps for an extension.

 
     TYPEMAP
     Netconfig *  T_PTROBJ  

This example will be used with the following Perl statements.

 
     use RPC;
     $netconf = getnetconfigent("udp");  

When Perl destroys the object referenced by $netconf it will send the object to the supplied XSUB DESTROY function. Perl cannot determine, and does not care, that this object is a C struct and not a Perl object. In this sense, there is no difference between the object created by the getnetconfigent() XSUB and an object created by a normal Perl subroutine.

The Typemap

The typemap is a collection of code fragments which are used by the xsubpp compiler to map C function parameters and values to Perl values. The typemap file may consist of three sections labelled TYPEMAP, INPUT, and OUTPUT. An unlabelled initial section is assumed to be a TYPEMAP section. 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. The section labels TYPEMAP, INPUT, or OUTPUT must begin in the first column on a line by themselves, and must be in uppercase.

The default typemap in the lib/ExtUtils directory of the Perl source contains many useful types which can be used by Perl extensions. Some extensions define additional typemaps which they keep in their own directory. These additional typemaps may reference INPUT and OUTPUT maps in the main typemap. The xsubpp compiler will allow the extension's own typemap to override any mappings which are in the default typemap.

Most extensions which require a custom typemap will need only the TYPEMAP section of the typemap file. The custom typemap used in the getnetconfigent() example shown earlier demonstrates what may be the typical use of extension typemaps. That typemap is used to equate a C structure with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown here. Note that the C type is separated from the XS type with a tab and that the C unary operator * is considered to be a part of the C type name.

 
	TYPEMAP
	Netconfig *<tab>T_PTROBJ  

Here's a more complicated example: suppose that you wanted struct netconfig to be blessed into the class 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 T_PTROBJ_SPECIAL that maps underscores to double-colons (::), and declare 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.

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 -g (--global) option with h2xs (see 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]);
  

REFERENCE

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  

typedef my_cxt_t

This struct typedef must always be called my_cxt_t -- the other CXT* macros assume the existence of the my_cxt_t typedef name.

Declare a typedef named 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;  

START_MY_CXT
Always place the START_MY_CXT macro directly after the declaration of my_cxt_t.
MY_CXT_INIT

The MY_CXT_INIT macro initialises storage for the my_cxt_t struct.

It must be called exactly once -- typically in a BOOT: section.

dMY_CXT
Use the dMY_CXT macro (a declaration) in all the functions that access MY_CXT.
MY_CXT

Use the MY_CXT macro to access members of the my_cxt_t struct. For example, if my_cxt_t is

 
    typedef struct {
        int index;
    } my_cxt_t;  

then use this to access the index member

 
    dMY_CXT;
    MY_CXT.index = 2;  

EXAMPLES

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

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

     #include <rpc/rpc.h>

     typedef struct netconfig Netconfig;

     MODULE = RPC  PACKAGE = RPC

     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 typemap: Custom typemap for RPC.xs.

 
     TYPEMAP
     Netconfig *  T_PTROBJ  

File RPC.pm: Perl module for the RPC extension.

 
     package RPC;

     require Exporter;
     require DynaLoader;
     @ISA = qw(Exporter DynaLoader);
     @EXPORT = qw(rpcb_gettime getnetconfigent);

     bootstrap RPC;
     1;  

File rpctest.pl: Perl test program for the RPC extension.

 
     use RPC;

     $netconf = getnetconfigent();
     $a = rpcb_gettime();
     print "time = $a\n";
     print "netconf = $netconf\n";

     $netconf = getnetconfigent("tcp");
     $a = rpcb_gettime("poplar");
     print "time = $a\n";
     print "netconf = $netconf\n";
  

XS VERSION

This document covers features supported by xsubpp 1.935.

AUTHOR

Originally written by Dean Roehrich <roehrich@cray.com>.

Maintained since 1996 by The Perl Porters <perlbug@perl.org>.

 

  

 

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