NAMEperlXStut - Tutorial for writing XSUBs
DESCRIPTIONThis tutorial will educate the reader on the steps involved in creating a Perl extension. The reader is assumed to have access to the perlguts manpage, the perlapi manpage and the perlxs manpage. This tutorial starts with very simple examples and becomes more complex, with each new example adding new features. Certain concepts may not be completely explained until later in the tutorial in order to slowly ease the reader into building extensions. This tutorial was written from a Unix point of view. Where I know them to be otherwise different for other platforms (e.g. Win32), I will list them. If you find something that was missed, please let me know.
SPECIAL NOTES
makeThis tutorial assumes that the make program that Perl is configured to
use is called
Version caveatWhen writing a Perl extension for general consumption, one should expect that the extension will be used with versions of Perl different from the version available on your machine. Since you are reading this document, the version of Perl on your machine is probably 5.005 or later, but the users of your extension may have more ancient versions. To understand what kinds of incompatibilities one may expect, and in the rare case that the version of Perl on your machine is older than this document, see the section on ``Troubleshooting these Examples'' for more information. If your extension uses some features of Perl which are not available on older releases of Perl, your users would appreciate an early meaningful warning. You would probably put this information into the README file, but nowadays installation of extensions may be performed automatically, guided by CPAN.pm module or other tools. In MakeMaker-based installations, Makefile.PL provides the earliest opportunity to perform version checks. One can put something like this in Makefile.PL for this purpose: eval { require 5.007 } or die <<EOD; ############ ### This module uses frobnication framework which is not available before ### version 5.007 of Perl. Upgrade your Perl before installing Kara::Mba. ############ EOD
Dynamic Loading versus Static LoadingIt is commonly thought that if a system does not have the capability to dynamically load a library, you cannot build XSUBs. This is incorrect. You can build them, but you must link the XSUBs subroutines with the rest of Perl, creating a new executable. This situation is similar to Perl 4. This tutorial can still be used on such a system. The XSUB build mechanism will check the system and build a dynamically-loadable library if possible, or else a static library and then, optionally, a new statically-linked executable with that static library linked in. Should you wish to build a statically-linked executable on a system which
can dynamically load libraries, you may, in all the following examples,
where the command `` If you have generated such a statically-linked executable by choice, then
instead of saying ``
TUTORIALNow let's go on with the show!
EXAMPLE 1Our first extension will be very simple. When we call the routine in the extension, it will print out a well-known message and return. Run `` The MANIFEST file contains the names of all the files just created in the Mytest directory. The file Makefile.PL should look something like this: use ExtUtils::MakeMaker; # See lib/ExtUtils/MakeMaker.pm for details of how to influence # the contents of the Makefile that is written. WriteMakefile( NAME => 'Mytest', VERSION_FROM => 'Mytest.pm', # finds $VERSION LIBS => [''], # e.g., '-lm' DEFINE => '', # e.g., '-DHAVE_SOMETHING' INC => '', # e.g., '-I/usr/include/other' ); The file Mytest.pm should start with something like this: package Mytest; use strict; use warnings; require Exporter; require DynaLoader; our @ISA = qw(Exporter DynaLoader); # Items to export into callers namespace by default. Note: do not export # names by default without a very good reason. Use EXPORT_OK instead. # Do not simply export all your public functions/methods/constants. our @EXPORT = qw( ); our $VERSION = '0.01'; bootstrap Mytest $VERSION; # Preloaded methods go here. # Autoload methods go after __END__, and are processed by the autosplit program. 1; __END__ # Below is the stub of documentation for your module. You better edit it! The rest of the .pm file contains sample code for providing documentation for the extension. Finally, the Mytest.xs file should look something like this: #include "EXTERN.h" #include "perl.h" #include "XSUB.h" MODULE = Mytest PACKAGE = Mytest Let's edit the .xs file by adding this to the end of the file: void hello() CODE: printf("Hello, world!\n"); It is okay for the lines starting at the ``CODE:'' line to not be indented. However, for readability purposes, it is suggested that you indent CODE: one level and the lines following one more level. Now we'll run `` % perl Makefile.PL Checking if your kit is complete... Looks good Writing Makefile for Mytest % Now, running make will produce output that looks something like this (some long lines have been shortened for clarity and some extraneous lines have been deleted): % make umask 0 && cp Mytest.pm ./blib/Mytest.pm perl xsubpp -typemap typemap Mytest.xs >Mytest.tc && mv Mytest.tc Mytest.c Please specify prototyping behavior for Mytest.xs (see perlxs manual) cc -c Mytest.c Running Mkbootstrap for Mytest () chmod 644 Mytest.bs LD_RUN_PATH="" ld -o ./blib/PA-RISC1.1/auto/Mytest/Mytest.sl -b Mytest.o chmod 755 ./blib/PA-RISC1.1/auto/Mytest/Mytest.sl cp Mytest.bs ./blib/PA-RISC1.1/auto/Mytest/Mytest.bs chmod 644 ./blib/PA-RISC1.1/auto/Mytest/Mytest.bs Manifying ./blib/man3/Mytest.3 % You can safely ignore the line about ``prototyping behavior'' - it is explained in the section ``The PROTOTYPES: Keyword'' in the perlxs manpage. If you are on a Win32 system, and the build process fails with linker errors for functions in the C library, check if your Perl is configured to use PerlCRT (running perl -V:libc should show you if this is the case). If Perl is configured to use PerlCRT, you have to make sure PerlCRT.lib is copied to the same location that msvcrt.lib lives in, so that the compiler can find it on its own. msvcrt.lib is usually found in the Visual C compiler's lib directory (e.g. C:/DevStudio/VC/lib). Perl has its own special way of easily writing test scripts, but for this example only, we'll create our own test script. Create a file called hello that looks like this: #! /opt/perl5/bin/perl use ExtUtils::testlib; use Mytest; Mytest::hello(); Now we make the script executable ( % ./hello Hello, world! %
EXAMPLE 2Now let's add to our extension a subroutine that will take a single numeric argument as input and return 0 if the number is even or 1 if the number is odd. Add the following to the end of Mytest.xs: int is_even(input) int input CODE: RETVAL = (input % 2 == 0); OUTPUT: RETVAL There does not need to be white space at the start of the `` Now re-run make to rebuild our new shared library. Now perform the same steps as before, generating a Makefile from the Makefile.PL file, and running make. In order to test that our extension works, we now need to look at the file test.pl. This file is set up to imitate the same kind of testing structure that Perl itself has. Within the test script, you perform a number of tests to confirm the behavior of the extension, printing ``ok'' when the test is correct, ``not ok'' when it is not. Change the print statement in the BEGIN block to print ``1..4'', and add the following code to the end of the file: print &Mytest::is_even(0) == 1 ? "ok 2" : "not ok 2", "\n"; print &Mytest::is_even(1) == 0 ? "ok 3" : "not ok 3", "\n"; print &Mytest::is_even(2) == 1 ? "ok 4" : "not ok 4", "\n"; We will be calling the test script through the command `` % make test PERL_DL_NONLAZY=1 /opt/perl5.004/bin/perl (lots of -I arguments) test.pl 1..4 ok 1 ok 2 ok 3 ok 4 %
What has gone on?The program h2xs is the starting point for creating extensions. In later examples we'll see how we can use h2xs to read header files and generate templates to connect to C routines. h2xs creates a number of files in the extension directory. The file Makefile.PL is a perl script which will generate a true Makefile to build the extension. We'll take a closer look at it later. The .pm and .xs files contain the meat of the extension. The .xs file holds the C routines that make up the extension. The .pm file contains routines that tell Perl how to load your extension. Generating the Makefile and running Invoking the test script via `` When Perl sees a In our case, Mytest.pm tells perl that it will need the Exporter and Dynamic
Loader extensions. It then sets the The two arrays The As a general rule, if the module is trying to be object-oriented then don't
export anything. If it's just a collection of functions and variables, then
you can export them via another array, called See the perlmod manpage for more information. The
Writing good test scriptsThe importance of writing good test scripts cannot be overemphasized. You should closely follow the ``ok/not ok'' style that Perl itself uses, so that it is very easy and unambiguous to determine the outcome of each test case. When you find and fix a bug, make sure you add a test case for it. By running ``
EXAMPLE 3Our third extension will take one argument as its input, round off that value, and set the argument to the rounded value. Add the following to the end of Mytest.xs: void round(arg) double arg CODE: if (arg > 0.0) { arg = floor(arg + 0.5); } else if (arg < 0.0) { arg = ceil(arg - 0.5); } else { arg = 0.0; } OUTPUT: arg Edit the Makefile.PL file so that the corresponding line looks like this: 'LIBS' => ['-lm'], # e.g., '-lm' Generate the Makefile and run make. Change the BEGIN block to print ``1..9'' and add the following to test.pl: $i = -1.5; &Mytest::round($i); print $i == -2.0 ? "ok 5" : "not ok 5", "\n"; $i = -1.1; &Mytest::round($i); print $i == -1.0 ? "ok 6" : "not ok 6", "\n"; $i = 0.0; &Mytest::round($i); print $i == 0.0 ? "ok 7" : "not ok 7", "\n"; $i = 0.5; &Mytest::round($i); print $i == 1.0 ? "ok 8" : "not ok 8", "\n"; $i = 1.2; &Mytest::round($i); print $i == 1.0 ? "ok 9" : "not ok 9", "\n"; Running `` Notice that in these new test cases, the argument passed to round was a scalar variable. You might be wondering if you can round a constant or literal. To see what happens, temporarily add the following line to test.pl: &Mytest::round(3); Run ``
What's new here?
Input and Output ParametersYou specify the parameters that will be passed into the XSUB on the The list of output parameters occurs at the very end of the function, just before after the OUTPUT: directive. The use of RETVAL tells Perl that you wish to send this value back as the return value of the XSUB function. In Example 3, we wanted the ``return value'' placed in the original variable which we passed in, so we listed it (and not RETVAL) in the OUTPUT: section.
The XSUBPP ProgramThe xsubpp program takes the XS code in the .xs file and translates it into C code, placing it in a file whose suffix is .c. The C code created makes heavy use of the C functions within Perl.
The TYPEMAP fileThe xsubpp program uses rules to convert from Perl's data types (scalar, array, etc.) to C's data types (int, char, etc.). These rules are stored in the typemap file ($PERLLIB/ExtUtils/typemap). This file is split into three parts. The first section maps various C data types to a name, which corresponds somewhat with the various Perl types. The second section contains C code which xsubpp uses to handle input parameters. The third section contains C code which xsubpp uses to handle output parameters. Let's take a look at a portion of the .c file created for our extension. The file name is Mytest.c: XS(XS_Mytest_round) { dXSARGS; if (items != 1) croak("Usage: Mytest::round(arg)"); { double arg = (double)SvNV(ST(0)); /* XXXXX */ if (arg > 0.0) { arg = floor(arg + 0.5); } else if (arg < 0.0) { arg = ceil(arg - 0.5); } else { arg = 0.0; } sv_setnv(ST(0), (double)arg); /* XXXXX */ } XSRETURN(1); } Notice the two lines commented with ``XXXXX''. If you check the first section of the typemap file, you'll see that doubles are of type T_DOUBLE. In the INPUT section, an argument that is T_DOUBLE is assigned to the variable arg by calling the routine SvNV on something, then casting it to double, then assigned to the variable arg. Similarly, in the OUTPUT section, once arg has its final value, it is passed to the sv_setnv function to be passed back to the calling subroutine. These two functions are explained in the perlguts manpage; we'll talk more later about what that ``ST(0)'' means in the section on the argument stack.
Warning about Output ArgumentsIn general, it's not a good idea to write extensions that modify their input parameters, as in Example 3. Instead, you should probably return multiple values in an array and let the caller handle them (we'll do this in a later example). However, in order to better accommodate calling pre-existing C routines, which often do modify their input parameters, this behavior is tolerated.
EXAMPLE 4In this example, we'll now begin to write XSUBs that will interact with pre-defined C libraries. To begin with, we will build a small library of our own, then let h2xs write our .pm and .xs files for us. Create a new directory called Mytest2 at the same level as the directory Mytest. In the Mytest2 directory, create another directory called mylib, and cd into that directory. Here we'll create some files that will generate a test library. These will include a C source file and a header file. We'll also create a Makefile.PL in this directory. Then we'll make sure that running make at the Mytest2 level will automatically run this Makefile.PL file and the resulting Makefile. In the mylib directory, create a file mylib.h that looks like this: #define TESTVAL 4 extern double foo(int, long, const char*); Also create a file mylib.c that looks like this: #include <stdlib.h> #include "./mylib.h" double foo(int a, long b, const char *c) { return (a + b + atof(c) + TESTVAL); } And finally create a file Makefile.PL that looks like this: use ExtUtils::MakeMaker; $Verbose = 1; WriteMakefile( NAME => 'Mytest2::mylib', SKIP => [qw(all static static_lib dynamic dynamic_lib)], clean => {'FILES' => 'libmylib$(LIBEEXT)'}, ); sub MY::top_targets { ' all :: static pure_all :: static static :: libmylib$(LIB_EXT) libmylib$(LIB_EXT): $(O_FILES) $(AR) cr libmylib$(LIB_EXT) $(O_FILES) $(RANLIB) libmylib$(LIB_EXT) '; } Make sure you use a tab and not spaces on the lines beginning with ``$(AR)'' and ``$(RANLIB)''. Make will not function properly if you use spaces. It has also been reported that the ``cr'' argument to $(AR) is unnecessary on Win32 systems. We will now create the main top-level Mytest2 files. Change to the directory above Mytest2 and run the following command: % h2xs -O -n Mytest2 ./Mytest2/mylib/mylib.h This will print out a warning about overwriting Mytest2, but that's okay. Our files are stored in Mytest2/mylib, and will be untouched. The normal Makefile.PL that h2xs generates doesn't know about the mylib directory. We need to tell it that there is a subdirectory and that we will be generating a library in it. Let's add the argument MYEXTLIB to the WriteMakefile call so that it looks like this: WriteMakefile( 'NAME' => 'Mytest2', 'VERSION_FROM' => 'Mytest2.pm', # finds $VERSION 'LIBS' => [''], # e.g., '-lm' 'DEFINE' => '', # e.g., '-DHAVE_SOMETHING' 'INC' => '', # e.g., '-I/usr/include/other' 'MYEXTLIB' => 'mylib/libmylib$(LIB_EXT)', ); and then at the end add a subroutine (which will override the pre-existing subroutine). Remember to use a tab character to indent the line beginning with ``cd''! sub MY::postamble { ' $(MYEXTLIB): mylib/Makefile cd mylib && $(MAKE) $(PASSTHRU) '; } Let's also fix the MANIFEST file so that it accurately reflects the contents of our extension. The single line that says ``mylib'' should be replaced by the following three lines: mylib/Makefile.PL mylib/mylib.c mylib/mylib.h To keep our namespace nice and unpolluted, edit the .pm file and change
the variable #include "mylib/mylib.h" And also add the following function definition to the end of the .xs file: double foo(a,b,c) int a long b const char * c OUTPUT: RETVAL Now we also need to create a typemap file because the default Perl doesn't currently support the const char * type. Create a file called typemap in the Mytest2 directory and place the following in it: const char * T_PV Now run perl on the top-level Makefile.PL. Notice that it also created a Makefile in the mylib directory. Run make and watch that it does cd into the mylib directory and run make in there as well. Now edit the test.pl script and change the BEGIN block to print ``1..4'', and add the following lines to the end of the script: print &Mytest2::foo(1, 2, "Hello, world!") == 7 ? "ok 2\n" : "not ok 2\n"; print &Mytest2::foo(1, 2, "0.0") == 7 ? "ok 3\n" : "not ok 3\n"; print abs(&Mytest2::foo(0, 0, "-3.4") - 0.6) <= 0.01 ? "ok 4\n" : "not ok 4\n"; (When dealing with floating-point comparisons, it is best to not check for equality, but rather that the difference between the expected and actual result is below a certain amount (called epsilon) which is 0.01 in this case) Run ``
What has happened here?Unlike previous examples, we've now run h2xs on a real include file. This has caused some extra goodies to appear in both the .pm and .xs files.
Anatomy of .xs fileThe .xs file of EXAMPLE 4 contained some new elements. To understand the meaning of these elements, pay attention to the line which reads MODULE = Mytest2 PACKAGE = Mytest2 Anything before this line is plain C code which describes which headers to include, and defines some convenience functions. No translations are performed on this part, apart from having embedded POD documentation skipped over (see the perlpod manpage) it goes into the generated output C file as is. Anything after this line is the description of XSUB functions. These descriptions are translated by xsubpp into C code which implements these functions using Perl calling conventions, and which makes these functions visible from Perl interpreter. Pay a special attention to the function This is quite typical for .xs files: usually the .xs file provides an interface to an existing C function. Then this C function is defined somewhere (either in an external library, or in the first part of .xs file), and a Perl interface to this function (i.e. ``Perl glue'') is described in the second part of .xs file. The situation in EXAMPLE 1, EXAMPLE 2, and EXAMPLE 3, when all the work is done inside the ``Perl glue'', is somewhat of an exception rather than the rule.
Getting the fat out of XSUBsIn EXAMPLE 4 the second part of .xs file contained the following description of an XSUB: double foo(a,b,c) int a long b const char * c OUTPUT: RETVAL Note that in contrast with EXAMPLE 1, EXAMPLE 2 and EXAMPLE 3, this description does not contain the actual code for what is done is done during a call to Perl function foo(). To understand what is going on here, one can add a CODE section to this XSUB: double foo(a,b,c) int a long b const char * c CODE: RETVAL = foo(a,b,c); OUTPUT: RETVAL However, these two XSUBs provide almost identical generated C code: xsubpp
compiler is smart enough to figure out the double foo(a,b,c) int a long b const char * c Can we do the same with an XSUB int is_even(input) int input CODE: RETVAL = (input % 2 == 0); OUTPUT: RETVAL of EXAMPLE 2? To do this, one needs to define a C function int is_even(int arg) { return (arg % 2 == 0); } is probably overkill for this. Something as simple as a #define is_even(arg) ((arg) % 2 == 0) After having this in the first part of .xs file, the ``Perl glue'' part becomes as simple as int is_even(input) int input This technique of separation of the glue part from the workhorse part has obvious tradeoffs: if you want to change a Perl interface, you need to change two places in your code. However, it removes a lot of clutter, and makes the workhorse part independent from idiosyncrasies of Perl calling convention. (In fact, there is nothing Perl-specific in the above description, a different version of xsubpp might have translated this to TCL glue or Python glue as well.)
More about XSUB argumentsWith the completion of Example 4, we now have an easy way to simulate some real-life libraries whose interfaces may not be the cleanest in the world. We shall now continue with a discussion of the arguments passed to the xsubpp compiler. When you specify arguments to routines in the .xs file, you are really passing three pieces of information for each argument listed. The first piece is the order of that argument relative to the others (first, second, etc). The second is the type of argument, and consists of the type declaration of the argument (e.g., int, char*, etc). The third piece is the calling convention for the argument in the call to the library function. While Perl passes arguments to functions by reference, C passes arguments by value; to implement a C function which modifies data of one of the ``arguments'', the actual argument of this C function would be a pointer to the data. Thus two C functions with declarations int string_length(char *s); int upper_case_char(char *cp); may have completely different semantics: the first one may inspect an array
of chars pointed by s, and the second one may immediately dereference One conveys this info to xsubpp by replacing int string_length(s) char * s int upper_case_char(cp) char &cp For example, consider: int foo(a,b) char &a char * b The first Perl argument to this function would be treated as a char and assigned to the variable a, and its address would be passed into the function foo. The second Perl argument would be treated as a string pointer and assigned to the variable b. The value of b would be passed into the function foo. The actual call to the function foo that xsubpp generates would look like this: foo(&a, b); xsubpp will parse the following function argument lists identically: char &a char&a char & a However, to help ease understanding, it is suggested that you place a ``&'' next to the variable name and away from the variable type), and place a ``*'' near the variable type, but away from the variable name (as in the call to foo above). By doing so, it is easy to understand exactly what will be passed to the C function -- it will be whatever is in the ``last column''. You should take great pains to try to pass the function the type of variable it wants, when possible. It will save you a lot of trouble in the long run.
The Argument StackIf we look at any of the C code generated by any of the examples except
example 1, you will notice a number of references to ST(n), where n is
usually 0. ``ST'' is actually a macro that points to the n'th argument
on the argument stack. When you list the arguments to the XSUB in the .xs file, that tells xsubpp which argument corresponds to which of the argument stack (i.e., the first one listed is the first argument, and so on). You invite disaster if you do not list them in the same order as the function expects them. The actual values on the argument stack are pointers to the values passed
in. When an argument is listed as being an OUTPUT value, its corresponding
value on the stack (i.e., double arg = (double)SvNV(ST(0)); /* Round the contents of the variable arg */ sv_setnv(ST(0), (double)arg); The arg variable is initially set by taking the value from ST(0), then is
stored back into XSUBs are also allowed to return lists, not just scalars. This must be done by manipulating stack values ST(0), ST(1), etc, in a subtly different way. See the perlxs manpage for details. XSUBs are also allowed to avoid automatic conversion of Perl function arguments
to C function arguments. See the perlxs manpage for details. Some people prefer
manual conversion by inspecting While experts may argue about these idioms, a novice to Perl guts may prefer a way which is as little Perl-guts-specific as possible, meaning automatic conversion and automatic call generation, as in Getting the fat out of XSUBs. This approach has the additional benefit of protecting the XSUB writer from future changes to the Perl API.
Extending your ExtensionSometimes you might want to provide some extra methods or subroutines to assist in making the interface between Perl and your extension simpler or easier to understand. These routines should live in the .pm file. Whether they are automatically loaded when the extension itself is loaded or only loaded when called depends on where in the .pm file the subroutine definition is placed. You can also consult the AutoLoader manpage for an alternate way to store and load your extra subroutines.
Documenting your ExtensionThere is absolutely no excuse for not documenting your extension. Documentation belongs in the .pm file. This file will be fed to pod2man, and the embedded documentation will be converted to the man page format, then placed in the blib directory. It will be copied to Perl's man page directory when the extension is installed. You may intersperse documentation and Perl code within the .pm file. In fact, if you want to use method autoloading, you must do this, as the comment inside the .pm file explains. See the perlpod manpage for more information about the pod format.
Installing your ExtensionOnce your extension is complete and passes all its tests, installing it is quite simple: you simply run ``make install''. You will either need to have write permission into the directories where Perl is installed, or ask your system administrator to run the make for you. Alternately, you can specify the exact directory to place the extension's files by placing a ``PREFIX=/destination/directory'' after the make install. (or in between the make and install if you have a brain-dead version of make). This can be very useful if you are building an extension that will eventually be distributed to multiple systems. You can then just archive the files in the destination directory and distribute them to your destination systems.
EXAMPLE 5In this example, we'll do some more work with the argument stack. The previous examples have all returned only a single value. We'll now create an extension that returns an array. This extension is very Unix-oriented (struct statfs and the statfs system call). If you are not running on a Unix system, you can substitute for statfs any other function that returns multiple values, you can hard-code values to be returned to the caller (although this will be a bit harder to test the error case), or you can simply not do this example. If you change the XSUB, be sure to fix the test cases to match the changes. Return to the Mytest directory and add the following code to the end of Mytest.xs: void statfs(path) char * path INIT: int i; struct statfs buf; PPCODE: i = statfs(path, &buf); if (i == 0) { XPUSHs(sv_2mortal(newSVnv(buf.f_bavail))); XPUSHs(sv_2mortal(newSVnv(buf.f_bfree))); XPUSHs(sv_2mortal(newSVnv(buf.f_blocks))); XPUSHs(sv_2mortal(newSVnv(buf.f_bsize))); XPUSHs(sv_2mortal(newSVnv(buf.f_ffree))); XPUSHs(sv_2mortal(newSVnv(buf.f_files))); XPUSHs(sv_2mortal(newSVnv(buf.f_type))); XPUSHs(sv_2mortal(newSVnv(buf.f_fsid[0]))); XPUSHs(sv_2mortal(newSVnv(buf.f_fsid[1]))); } else { XPUSHs(sv_2mortal(newSVnv(errno))); } You'll also need to add the following code to the top of the .xs file, just after the include of ``XSUB.h'': #include <sys/vfs.h> Also add the following code segment to test.pl while incrementing the ``1..9'' string in the BEGIN block to ``1..11'': @a = &Mytest::statfs("/blech"); print ((scalar(@a) == 1 && $a[0] == 2) ? "ok 10\n" : "not ok 10\n"); @a = &Mytest::statfs("/"); print scalar(@a) == 9 ? "ok 11\n" : "not ok 11\n";
New Things in this ExampleThis example added quite a few new concepts. We'll take them one at a time.
EXAMPLE 6In this example, we will accept a reference to an array as an input parameter, and return a reference to an array of hashes. This will demonstrate manipulation of complex Perl data types from an XSUB. This extension is somewhat contrived. It is based on the code in the previous example. It calls the statfs function multiple times, accepting a reference to an array of filenames as input, and returning a reference to an array of hashes containing the data for each of the filesystems. Return to the Mytest directory and add the following code to the end of Mytest.xs: SV * multi_statfs(paths) SV * paths INIT: AV * results; I32 numpaths = 0; int i, n; struct statfs buf; if ((!SvROK(paths)) || (SvTYPE(SvRV(paths)) != SVt_PVAV) || ((numpaths = av_len((AV *)SvRV(paths))) < 0)) { XSRETURN_UNDEF; } results = (AV *)sv_2mortal((SV *)newAV()); CODE: for (n = 0; n <= numpaths; n++) { HV * rh; STRLEN l; char * fn = SvPV(*av_fetch((AV *)SvRV(paths), n, 0), l); i = statfs(fn, &buf); if (i != 0) { av_push(results, newSVnv(errno)); continue; } rh = (HV *)sv_2mortal((SV *)newHV()); hv_store(rh, "f_bavail", 8, newSVnv(buf.f_bavail), 0); hv_store(rh, "f_bfree", 7, newSVnv(buf.f_bfree), 0); hv_store(rh, "f_blocks", 8, newSVnv(buf.f_blocks), 0); hv_store(rh, "f_bsize", 7, newSVnv(buf.f_bsize), 0); hv_store(rh, "f_ffree", 7, newSVnv(buf.f_ffree), 0); hv_store(rh, "f_files", 7, newSVnv(buf.f_files), 0); hv_store(rh, "f_type", 6, newSVnv(buf.f_type), 0); av_push(results, newRV((SV *)rh)); } RETVAL = newRV((SV *)results); OUTPUT: RETVAL And add the following code to test.pl, while incrementing the ``1..11'' string in the BEGIN block to ``1..13'': $results = Mytest::multi_statfs([ '/', '/blech' ]); print ((ref $results->[0]) ? "ok 12\n" : "not ok 12\n"); print ((! ref $results->[1]) ? "ok 13\n" : "not ok 13\n");
New Things in this ExampleThere are a number of new concepts introduced here, described below:
EXAMPLE 7 (Coming Soon)XPUSH args AND set RETVAL AND assign return value to array
EXAMPLE 8 (Coming Soon)Setting $!
EXAMPLE 9 (Coming Soon)Getting fd's from filehandles
Troubleshooting these ExamplesAs mentioned at the top of this document, if you are having problems with these example extensions, you might see if any of these help you.
See alsoFor more information, consult the perlguts manpage, the perlapi manpage, the perlxs manpage, the perlmod manpage, and the perlpod manpage.
AuthorJeff Okamoto <okamoto@corp.hp.com> Reviewed and assisted by Dean Roehrich, Ilya Zakharevich, Andreas Koenig, and Tim Bunce.
Last Changed1999/11/30
|