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12.15. Using h2xs to Make a Module with C CodeProblemYou'd like to access your system's unique C functions from Perl. SolutionUse the h2xs tool to generate the necessary template files, fill the files in appropriately, and then type: % perl Makefile.PL % make DiscussionA Perl module need not be written solely in Perl. As with any other module, first pick a module name and use h2xs on it. We'll make a First, we run the following command: % h2xs -cn FineTime If we had a .h file with function prototype declarations, we could include that, but because we're writing this one from scratch, we'll use the -c flag to omit building code to translate any
Before we can type % perl Makefile.PL If the XS code calls library code that isn't in the normal set of libraries Perl links from, add one more line to Makefile.PL first. For example, if we wanted to link against the librpm.a library, which lives in the /usr/redhat/lib directory, we'd change the line of Makefile.PL that reads: 'LIBS' => [''], # e.g., '-lm' so that it says: 'LIBS' => ['-L/usr/redhat/lib -lrpm'], If the module is to be installed somewhere other than the local site_lib directory, specify that on the command line: % perl Makefile.PL LIB=~/perllib Finally, edit the FineTime.pm and FineTime.xs files. In the first case, most of the work has been done for us. We just set up the export list with the function to be exported. This time we put it in package FineTime; use strict; use vars qw($VERSION @ISA @EXPORT_OK); require Exporter; require DynaLoader; @ISA = qw(Exporter DynaLoader); @EXPORT_OK = qw(time); $VERSION = '0.01'; bootstrap FineTime $VERSION; 1; The make process will automatically translate FineTime.xs into a FineTime.c file and eventually into a shared library, probably called FineTime.so on most platforms. The utility that does this translation is xsubpp, which is described in its own manpage and perlxstut (1). The build will call xsubpp automatically. Besides a strong C background, you also need to understand the C-to-Perl interface, called XS (external subroutine). The details and nuances of XS are beyond the scope of this book. The automatically generated FineTime.xs had the Perl-specific include files in it, as well as the MODULE declaration. We've added some extra includes and written the code for the new Here's the FineTime.xs we used: #include <unistd.h> #include <sys/time.h> #include "EXTERN.h" #include "perl.h" #include "XSUB.h" MODULE = FineTime PACKAGE = FineTime double time() CODE: struct timeval tv; gettimeofday(&tv,0); RETVAL = tv.tv_sec + ((double) tv.tv_usec) / 1000000; OUTPUT: RETVAL Defining a function by the same name as one from the standard C library won't cause a problem when it's compiled because that's not its real name. That's just what Perl calls it. The C linker will see it as Here's what happened with make install (with some edits): % make install mkdir ./blib/lib/auto/FineTime cp FineTime.pm ./blib/lib/FineTime.pm /usr/local/bin/perl -I/usr/lib/perl5/i686-linux/5.00403 -I/usr/lib/perl5 /usr/lib/perl5/ExtUtils/xsubpp -typemap /usr/lib/perl5/ExtUtils/typemap FineTime.xs FineTime.tc && mv FineTime.tc FineTime.ccc -c -Dbool=char -DHAS_BOOL -O2-DVERSION=\"0.01\" -DXS_VERSION=\"0.01\" -fpic -I/usr/lib/perl5/i686-linux/5.00403/CORE FineTime.cRunning Mkbootstrap for FineTime () chmod 644 FineTime.bs LD_RUN_PATH="" cc -o blib/arch/auto/FineTime/FineTime.so -shared -L/usr/local/lib FineTime.o chmod 755 blib/arch/auto/FineTime/FineTime.so cp FineTime.bs ./blib/arch/auto/FineTime/FineTime.bs chmod 644 blib/arch/auto/FineTime/FineTime.bs Installing /home/tchrist/perllib/i686-linux/./auto/FineTime/FineTime.so Installing /home/tchrist/perllib/i686-linux/./auto/FineTime/FineTime.bs Installing /home/tchrist/perllib/./FineTime.pm Writing /home/tchrist/perllib/i686-linux/auto/FineTime/.packlist Appending installation info to /home/tchrist/perllib/i686-linux/perllocal.pod Once this is all done, we'll be able to type something like this into the shell: % perl -I ~/perllib -MFineTime=time -le '1 while print time()' | head See AlsoChapters 18 through 20 in Advanced Perl Programming; perlxstut (1) and perlxs (1) to learn how to call C from Perl; perlcall (1) and perlguts (1) to understand the internal Perl API; perlembed (1) to learn how to call Perl from C; the the documentation for the standard ExtUtils::MakeMaker module, h2ph (1) and xsubpp (1); http://www.perl.com/CPAN/authors/Dean_Roehrich/, which contains Dean's comprehensive XS cookbook that includes directions on interface with C++ |