Subroutine libraries in Perl are called modules, and modules that contain xsubs are called XS modules. Perl provides a framework for developing, packaging, distributing, and installing modules.
It may be desirable for a Perl program to invoke a C subroutine in order to handle very CPU or memory intensive tasks, to interface with hardware or low-level system facilities, or to make use of existing C subroutine libraries.
The Perl interpreter is a C program, so in principle there is no obstacle to calling from Perl to C. However, the XS interface is complex[why?] and highly technical, and using it requires some understanding of the interpreter. The earliest reference on the subject was the POD.
Wrappersedit
It is possible to write XS modules that wrapC++ code. Doing so is mostly a matter of configuring the module build system.[1]
Example codeedit
The following shows an XS module that exposes a function concat() to concatenate two strings (i.e., the equivalent of Perl’s . operator).
The first four lines (#define and #include statements) are standard boilerplate.
After then follow any number of plain C functions that are callable locally.
The section that starts with MODULE = Demo::XSModule defines the Perl interface to this code using the actual XS macro language. Note that the C code under the CODE: section calls the _do_sv_catsv() pure-C function that was defined in the prior section.
Perl’s documentation explains the meaning and purpose of all of the “special” symbols (e.g., aTHX_ and RETVAL) shown above.
To make this module available to Perl it must be compiled. Build tools like ExtUtils::MakeMaker can do this automatically. (To build manually: the xsubpp tool parses an XS module and outputs C source code; that source code is then compiled to a shared library and placed in a directory where Perl can find it.) Perl code then uses a module like XSLoader to load the compiled XS module. At this point Perl can call Demo::XSModule::concat('foo', 'bar') and receive back a string foobar, as if concat() were itself written in Perl.
Note that, for building Perl interfaces to preexisting C libraries, the h2xs[further explanation needed] can automate much of the creation of the XS file itself.
Difficultiesedit
Creation and maintenance of XS modules requires expertise with C itself as well as Perl’s extensive C API. XS modules may only be installed if a C compiler and the header files that the Perl interpreter was compiled against are available. Also, new versions of Perl may break binary compatibility requiring XS modules to be recompiled.
See alsoedit
SWIG, an alternative to XS which also supports calling C and C++ functions from several other languages.
FFI, a mechanism which enables calling routines written in another language.
Referencesedit
^. johnkeiser.com. August 27, 2001. Archived from the original on December 11, 2001. Retrieved May 5, 2005.
Jenness, Tim & Cozens, Simon (2002). "Extending and Embedding Perl". Greenwich: Manning Publications Co. ISBN1-930110-82-0
External linksedit
Perl XS application programming interface
perlxstut Perl XS tutorial
Perl internal functions for those doing extensions
perlapi Perl API listing (autogenerated)
tutorial
building XS modules for C++
xs-fun XS is fun: a simple and easy tutorial on writing Perl XS
April 18, 2024
perl, perl, foreign, function, interface, through, which, program, call, subroutine, xsub, abbreviation, extendable, subroutine, also, refers, glue, language, specifying, calling, interfaces, supporting, such, interfaces, below, contents, background, perl, int. XS is a Perl foreign function interface through which a program can call a C or C subroutine XS or xsub is an abbreviation of eXtendable Subroutine XS also refers to a glue language for specifying calling interfaces supporting such interfaces see below Contents 1 Background 1 1 Perl interpreter 2 Wrappers 3 Example code 4 Difficulties 5 See also 6 References 7 External linksBackground editSubroutine libraries in Perl are called modules and modules that contain xsubs are called XS modules Perl provides a framework for developing packaging distributing and installing modules It may be desirable for a Perl program to invoke a C subroutine in order to handle very CPU or memory intensive tasks to interface with hardware or low level system facilities or to make use of existing C subroutine libraries Perl interpreter edit Main article calling convention The Perl interpreter is a C program so in principle there is no obstacle to calling from Perl to C However the XS interface is complex why and highly technical and using it requires some understanding of the interpreter The earliest reference on the subject was the perlguts POD Wrappers editIt is possible to write XS modules that wrap C code Doing so is mostly a matter of configuring the module build system 1 Example code editThe following shows an XS module that exposes a function concat to concatenate two strings i e the equivalent of Perl s operator define PERL NO GET CONTEXT include EXTERN h include perl h include XSUB h SV do sv catsv pTHX SV one sv SV two sv SV one copy newSVsv one sv sv catsv one copy two sv return one copy MODULE Demo XSModule PACKAGE Demo XSModule SV concat SV one sv SV two sv CODE SV to return do sv catsv aTHX one sv two sv RETVAL to return OUTPUT RETVAL The first four lines define and include statements are standard boilerplate After then follow any number of plain C functions that are callable locally The section that starts with MODULE Demo XSModule defines the Perl interface to this code using the actual XS macro language Note that the C code under the CODE section calls the do sv catsv pure C function that was defined in the prior section Perl s documentation explains the meaning and purpose of all of the special symbols e g aTHX and RETVAL shown above To make this module available to Perl it must be compiled Build tools like ExtUtils MakeMaker can do this automatically To build manually the xsubpp tool parses an XS module and outputs C source code that source code is then compiled to a shared library and placed in a directory where Perl can find it Perl code then uses a module like XSLoader to load the compiled XS module At this point Perl can call Demo XSModule concat foo bar and receive back a string foobar as if concat were itself written in Perl Note that for building Perl interfaces to preexisting C libraries the h2xs further explanation needed can automate much of the creation of the XS file itself Difficulties editCreation and maintenance of XS modules requires expertise with C itself as well as Perl s extensive C API XS modules may only be installed if a C compiler and the header files that the Perl interpreter was compiled against are available Also new versions of Perl may break binary compatibility requiring XS modules to be recompiled See also editSWIG an alternative to XS which also supports calling C and C functions from several other languages FFI a mechanism which enables calling routines written in another language References edit Gluing C And Perl Together johnkeiser com August 27 2001 Archived from the original on December 11 2001 Retrieved May 5 2005 Jenness Tim amp Cozens Simon 2002 Extending and Embedding Perl Greenwich Manning Publications Co ISBN 1 930110 82 0External links editperlxs Perl XS application programming interface perlxstut Perl XS tutorial perlguts Perl internal functions for those doing extensions perlapi Perl API listing autogenerated XS Mechanics tutorial Perl and C building XS modules for C xs fun XS is fun a simple and easy tutorial on writing Perl XS Retrieved from https en wikipedia org w index php title XS Perl amp oldid 1177580076, wikipedia, wiki, book, books, library,
