Wrapping C++ with Perl Brian Magill March 2009

SWIG (Simplified Wrapper and Interface Generator) Wraps C++ with Perl or other computer languages Generates the connecting wrapper code for both C++ and Perl (or other target language). C++ code then compiled and linked into a library Perl scripts call Perl wrapper, which in turn calls C++ library

Motivation Code high level functionality in Perl: – File, Database I/O – String manipulation, pattern matching, etc. – Sorting, organizing data – Applying functions to elements of arrays – Filtering out elements from arrays Code Toolkit interfaces and computationally intensive code in C++ Need a better way to integrate these two languages

File Generation example.i example.h (other header files) example.pm example_wrap.cxx SWIG example.cpp (other CPP files) example.dylib (MacIntosh) g++ example.so (Other Unix Platforms) or example_wrap.cxx

SWIG Interface File Tells which routines are to be wrapped Wraps built-in C/C++ data types Wraps STL vectors and strings Can wrap more complex data structures Can specify error handling

Example Interface File %include "exception.i" %exception { try { $action } catch (const std::exception &e) { SWIG_exception_fail(SWIG_RuntimeError, e.what()); } %module example %{ /* Put headers and other declarations here */ #include "example.h" %} %include "std_vector.i" %include "std_string.i" %template(IntVector) std::vector ; %template(DoubleVector) std::vector ; %include "example.h"

Running the SWIG Command  swig –c++ -perl5 example.i Produces: example_wrap.cxx … C++ Wrapper example.pm … Perl Wrapper

Compiling and Linking C++ Example # # Make file: MacIntosh version # all: swig -c++ -perl5 example.i g++ -c example.cpp example_wrap.cxx \ `/usr/bin/perl -MExtUtils::Embed -e ccopts` g++ -dynamiclib -single_module -flat_namespace \ -undefined suppress -o example.dylib example.o example_wrap.o clean: rm *.o *.cxx purge: rm *.o *.dylib *.cxx *.pm

Compiling and Linking C++ Example # # SWIG example make file for Linux # all: swig -c++ -perl example.i g++ -c example.cpp example_wrap.cxx \ `/usr/bin/perl -MExtUtils::Embed -e ccopts` g++ -shared example.o example_wrap.o -L /usr/lib/ \ -lperl -o example.so clean: rm *.o *.cxx purge: rm *.o *.so *.cxx *.pm

Resulting C++ Library Differs with platform and operating system On Mac OS X a *.dylib library is created On Unix Systems a shared (*.so) library is created C++ library needs to be in same location as Perl wrapper.

Simple Example /* Example.h */ #include #define PGSd_EOS_AM 2222 #define PGSd_EOS_PM 3333 double average(std::vector v); std::vector half(const std::vector & v); std::string TestMod(const std::string &s);

Simple Example (Con’t) // // example.cpp // #include #include "example.h" using namespace std; double average(vector v) { return (accumulate(v.begin(), v.end(), 0.0))/v.size();} vector half(const vector & v) { vector w(v); for( unsigned long i = 0; i < w.size(); i++) w[i] /= 2.0; return w; } std::string TestMod(const std::string &s) {return string("TestOutput: ") + s;}

#!/usr/bin/perl # # TestExample.pl # use strict; use example; = (0..3); = (0.0, 1.5, 1.0, 1.5); print "Integer Array Values: "; map { print "$_,"; print "\nAverage = ", "\n"; print "\nTry passing in an array of doubles: \n"; eval {"Average = ", "\n"; }; print "\tError encountered: if # print "Double Array Values: "; map { print "$_,"; my $ref = print "\nHalved Values: "; map { print "$_,"; print "\n\n"; # my $str = "Hello World!\n"; print example::TestMod($str); print "\nConstant PGSd_EOS_AM = ", $example::PGSd_EOS_AM, "\n"; print "Constant PGSd_EOS_PM = ", $example::PGSd_EOS_PM, "\n\n";

TestExample.pl’s Output Integer Array Values: 0,1,2,3, Average = 1.5 Try passing in an array of doubles: Error encountered: RuntimeError Type error in argument 1 of average. Expected an array of int Double Array Values: 0,1.5,1,1.5, Halved Values: 0,0.75,0.5,0.75, TestOutput: Hello World! Constant PGSd_EOS_AM = 2222 Constant PGSd_EOS_PM = 3333

Suggestions Use built-in or STL types arguments wherever possible Otherwise use custom built C++ data classes consisting of above types Link C++ code as shared objects if possible Place exception handling first in interface file Use SWIG_exception_fail

References /CERES/instrument/home/bmagill/ComputerLanguages/Perl/SWIG/SWIG_C++/ /CERES/instrument/home/bmagill/SolarAngle/Configured/src/