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PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) NNNNAAAAMMMMEEEE perlXStut - Tutorial for XSUB's DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN This tutorial will educate the reader on the steps involved in creating a Perl extension. The reader is assumed to have access to the _p_e_r_l_g_u_t_s manpage and the _p_e_r_l_x_s 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. VVVVEEEERRRRSSSSIIIIOOOONNNN CCCCAAAAVVVVEEEEAAAATTTT This tutorial tries hard to keep up with the latest development versions of Perl. This often means that it is sometimes in advance of the latest released version of Perl, and that certain features described here might not work on earlier versions. This section will keep track of when various features were added to Perl 5. +o In versions of 5.002 prior to version beta 3, then the line in the .xs file about "PROTOTYPES: DISABLE" will cause a compiler error. Simply remove that line from the file. +o In versions of 5.002 prior to version 5.002b1h, the test.pl file was not automatically created by h2xs. This means that you cannot say "make test" to run the test script. You will need to add the following line before the "use extension" statement: uuuusssseeee lllliiiibbbb ''''....////bbbblllliiiibbbb'''';;;; +o In versions 5.000 and 5.001, instead of using the above line, you will need to use the following line: BBBBEEEEGGGGIIIINNNN {{{{ uuuunnnnsssshhhhiiiifffftttt((((@@@@IIIINNNNCCCC,,,, """"....////bbbblllliiiibbbb"""")))) }}}} +o This document assumes that the executable named "perl" is Perl version 5. Some systems may have installed Perl version 5 as "perl5". DDDDYYYYNNNNAAAAMMMMIIIICCCC VVVVEEEERRRRSSSSUUUUSSSS SSSSTTTTAAAATTTTIIIICCCC It is commonly thought that if a system does not have the capability to dynamically load a library, you cannot build XSUB's. This is incorrect. You _c_a_n build them, but you must link the XSUB's subroutines with the rest of Perl, 12/Feb/96 perl 5.002 with 1 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) 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 "make" with no arguments is executed, run the command "make perl" instead. If you have generated such a statically-linked executable by choice, then instead of saying "make test", you should say "make test_static". On systems that cannot build dynamically-loadable libraries at all, simply saying "make test" is sufficient. EEEEXXXXAAAAMMMMPPPPLLLLEEEE 1111 Our 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 "h2xs -A -n Mytest". This creates a directory named Mytest, possibly under ext/ if that directory exists in the current working directory. Several files will be created in the Mytest dir, including MANIFEST, Makefile.PL, Mytest.pm, Mytest.xs, test.pl, and Changes. The MANIFEST file contains the names of all the files created. The file Makefile.PL should look something like this: uuuusssseeee EEEExxxxttttUUUUttttiiiillllssss::::::::MMMMaaaakkkkeeeeMMMMaaaakkkkeeeerrrr;;;; #### SSSSeeeeeeee lllliiiibbbb////EEEExxxxttttUUUUttttiiiillllssss////MMMMaaaakkkkeeeeMMMMaaaakkkkeeeerrrr....ppppmmmm ffffoooorrrr ddddeeeettttaaaaiiiillllssss ooooffff hhhhoooowwww ttttoooo iiiinnnnfffflllluuuueeeennnncccceeee #### tttthhhheeee ccccoooonnnntttteeeennnnttttssss ooooffff tttthhhheeee MMMMaaaakkkkeeeeffffiiiilllleeee tttthhhhaaaatttt iiiissss wwwwrrrriiiitttttttteeeennnn.... WWWWrrrriiiitttteeeeMMMMaaaakkkkeeeeffffiiiilllleeee(((( ''''NNNNAAAAMMMMEEEE'''' ====>>>> ''''MMMMyyyytttteeeesssstttt'''',,,, ''''VVVVEEEERRRRSSSSIIIIOOOONNNN____FFFFRRRROOOOMMMM'''' ====>>>> ''''MMMMyyyytttteeeesssstttt....ppppmmmm'''',,,, #### ffffiiiinnnnddddssss $$$$VVVVEEEERRRRSSSSIIIIOOOONNNN ''''LLLLIIIIBBBBSSSS'''' ====>>>> [[[['''''''']]]],,,, #### eeee....gggg....,,,, ''''----llllmmmm'''' ''''DDDDEEEEFFFFIIIINNNNEEEE'''' ====>>>> '''''''',,,, #### eeee....gggg....,,,, ''''----DDDDHHHHAAAAVVVVEEEE____SSSSOOOOMMMMEEEETTTTHHHHIIIINNNNGGGG'''' ''''IIIINNNNCCCC'''' ====>>>> '''''''',,,, #### eeee....gggg....,,,, ''''----IIII////uuuussssrrrr////iiiinnnncccclllluuuuddddeeee////ooootttthhhheeeerrrr'''' ))));;;; The file Mytest.pm should start with something like this: ppppaaaacccckkkkaaaaggggeeee MMMMyyyytttteeeesssstttt;;;; 12/Feb/96 perl 5.002 with 2 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) rrrreeeeqqqquuuuiiiirrrreeee EEEExxxxppppoooorrrrtttteeeerrrr;;;; rrrreeeeqqqquuuuiiiirrrreeee DDDDyyyynnnnaaaaLLLLooooaaaaddddeeeerrrr;;;; @@@@IIIISSSSAAAA ==== qqqqwwww((((EEEExxxxppppoooorrrrtttteeeerrrr DDDDyyyynnnnaaaaLLLLooooaaaaddddeeeerrrr))));;;; #### IIIItttteeeemmmmssss ttttoooo eeeexxxxppppoooorrrrtttt iiiinnnnttttoooo ccccaaaalllllllleeeerrrrssss nnnnaaaammmmeeeessssppppaaaacccceeee bbbbyyyy ddddeeeeffffaaaauuuulllltttt.... NNNNooootttteeee:::: ddddoooo nnnnooootttt eeeexxxxppppoooorrrrtttt #### nnnnaaaammmmeeeessss bbbbyyyy ddddeeeeffffaaaauuuulllltttt wwwwiiiitttthhhhoooouuuutttt aaaa vvvveeeerrrryyyy ggggoooooooodddd rrrreeeeaaaassssoooonnnn.... UUUUsssseeee EEEEXXXXPPPPOOOORRRRTTTT____OOOOKKKK iiiinnnnsssstttteeeeaaaadddd.... #### DDDDoooo nnnnooootttt ssssiiiimmmmppppllllyyyy eeeexxxxppppoooorrrrtttt aaaallllllll yyyyoooouuuurrrr ppppuuuubbbblllliiiicccc ffffuuuunnnnccccttttiiiioooonnnnssss////mmmmeeeetttthhhhooooddddssss////ccccoooonnnnssssttttaaaannnnttttssss.... @@@@EEEEXXXXPPPPOOOORRRRTTTT ==== qqqqwwww(((( ))));;;; $$$$VVVVEEEERRRRSSSSIIIIOOOONNNN ==== ''''0000....00001111'''';;;; bbbboooooooottttssssttttrrrraaaapppp MMMMyyyytttteeeesssstttt $$$$VVVVEEEERRRRSSSSIIIIOOOONNNN;;;; #### PPPPrrrreeeellllooooaaaaddddeeeedddd mmmmeeeetttthhhhooooddddssss ggggoooo hhhheeeerrrreeee.... #### AAAAuuuuttttoooollllooooaaaadddd mmmmeeeetttthhhhooooddddssss ggggoooo aaaafffftttteeeerrrr ________EEEENNNNDDDD________,,,, aaaannnndddd aaaarrrreeee pppprrrroooocccceeeesssssssseeeedddd bbbbyyyy tttthhhheeee aaaauuuuttttoooosssspppplllliiiitttt pppprrrrooooggggrrrraaaammmm.... 1111;;;; ________EEEENNNNDDDD________ #### BBBBeeeelllloooowwww iiiissss tttthhhheeee ssssttttuuuubbbb ooooffff ddddooooccccuuuummmmeeeennnnttttaaaattttiiiioooonnnn ffffoooorrrr yyyyoooouuuurrrr mmmmoooodddduuuulllleeee.... YYYYoooouuuu bbbbeeeetttttttteeeerrrr eeeeddddiiiitttt iiiitttt!!!! And the Mytest.xs file should look something like this: ####iiiiffffddddeeeeffff ________ccccpppplllluuuusssspppplllluuuussss eeeexxxxtttteeeerrrrnnnn """"CCCC"""" {{{{ ####eeeennnnddddiiiiffff ####iiiinnnncccclllluuuuddddeeee """"EEEEXXXXTTTTEEEERRRRNNNN....hhhh"""" ####iiiinnnncccclllluuuuddddeeee """"ppppeeeerrrrllll....hhhh"""" ####iiiinnnncccclllluuuuddddeeee """"XXXXSSSSUUUUBBBB....hhhh"""" ####iiiiffffddddeeeeffff ________ccccpppplllluuuusssspppplllluuuussss }}}} ####eeeennnnddddiiiiffff PPPPRRRROOOOTTTTOOOOTTTTYYYYPPPPEEEESSSS:::: DDDDIIIISSSSAAAABBBBLLLLEEEE MMMMOOOODDDDUUUULLLLEEEE ==== MMMMyyyytttteeeesssstttt PPPPAAAACCCCKKKKAAAAGGGGEEEE ==== MMMMyyyytttteeeesssstttt Let's edit the .xs file by adding this to the end of the file: vvvvooooiiiidddd hhhheeeelllllllloooo(((()))) CCCCOOOODDDDEEEE:::: pppprrrriiiinnnnttttffff((((""""HHHHeeeelllllllloooo,,,, wwwwoooorrrrlllldddd!!!!\\\\nnnn""""))));;;; Now we'll run "perl Makefile.PL". This will create a real Makefile, which make needs. It's output looks something like: 12/Feb/96 perl 5.002 with 3 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) %%%% ppppeeeerrrrllll MMMMaaaakkkkeeeeffffiiiilllleeee....PPPPLLLL CCCChhhheeeecccckkkkiiiinnnngggg iiiiffff yyyyoooouuuurrrr kkkkiiiitttt iiiissss ccccoooommmmpppplllleeeetttteeee............ LLLLooooooookkkkssss ggggoooooooodddd WWWWrrrriiiittttiiiinnnngggg MMMMaaaakkkkeeeeffffiiiilllleeee ffffoooorrrr MMMMyyyytttteeeesssstttt %%%% Now, running make will produce output that looks something like this (some long lines shortened for clarity): %%%% mmmmaaaakkkkeeee uuuummmmaaaasssskkkk 0000 &&&&&&&& ccccpppp MMMMyyyytttteeeesssstttt....ppppmmmm ....////bbbblllliiiibbbb////MMMMyyyytttteeeesssstttt....ppppmmmm ppppeeeerrrrllll xxxxssssuuuubbbbpppppppp ----ttttyyyyppppeeeemmmmaaaapppp ttttyyyyppppeeeemmmmaaaapppp MMMMyyyytttteeeesssstttt....xxxxssss >>>>MMMMyyyytttteeeesssstttt....ttttcccc &&&&&&&& mmmmvvvv MMMMyyyytttteeeesssstttt....ttttcccc MMMMyyyytttteeeesssstttt....cccc cccccccc ----cccc MMMMyyyytttteeeesssstttt....cccc RRRRuuuunnnnnnnniiiinnnngggg MMMMkkkkbbbboooooooottttssssttttrrrraaaapppp ffffoooorrrr MMMMyyyytttteeeesssstttt (((()))) cccchhhhmmmmoooodddd 666644444444 MMMMyyyytttteeeesssstttt....bbbbssss LLLLDDDD____RRRRUUUUNNNN____PPPPAAAATTTTHHHH===="""""""" lllldddd ----oooo ....////bbbblllliiiibbbb////PPPPAAAA----RRRRIIIISSSSCCCC1111....1111////aaaauuuuttttoooo////MMMMyyyytttteeeesssstttt////MMMMyyyytttteeeesssstttt....ssssllll ----bbbb MMMMyyyytttteeeesssstttt....oooo cccchhhhmmmmoooodddd 777755555555 ....////bbbblllliiiibbbb////PPPPAAAA----RRRRIIIISSSSCCCC1111....1111////aaaauuuuttttoooo////MMMMyyyytttteeeesssstttt////MMMMyyyytttteeeesssstttt....ssssllll ccccpppp MMMMyyyytttteeeesssstttt....bbbbssss ....////bbbblllliiiibbbb////PPPPAAAA----RRRRIIIISSSSCCCC1111....1111////aaaauuuuttttoooo////MMMMyyyytttteeeesssstttt////MMMMyyyytttteeeesssstttt....bbbbssss cccchhhhmmmmoooodddd 666644444444 ....////bbbblllliiiibbbb////PPPPAAAA----RRRRIIIISSSSCCCC1111....1111////aaaauuuuttttoooo////MMMMyyyytttteeeesssstttt////MMMMyyyytttteeeesssstttt....bbbbssss Now, although there is already a test.pl template ready for us, for this example only, we'll create a special test script. Create a file called hello that looks like this: ####!!!! ////oooopppptttt////ppppeeeerrrrllll5555////bbbbiiiinnnn////ppppeeeerrrrllll uuuusssseeee lllliiiibbbb ''''....////bbbblllliiiibbbb'''';;;; uuuusssseeee MMMMyyyytttteeeesssstttt;;;; MMMMyyyytttteeeesssstttt::::::::hhhheeeelllllllloooo(((())));;;; Now we run the script and we should see the following output: %%%% ppppeeeerrrrllll hhhheeeelllllllloooo HHHHeeeelllllllloooo,,,, wwwwoooorrrrlllldddd!!!! %%%% EEEEXXXXAAAAMMMMPPPPLLLLEEEE 2222 Now let's add to our extension a subroutine that will take a single argument and return 0 if the argument is even, 1 if the argument is odd. Add the following to the end of Mytest.xs: 12/Feb/96 perl 5.002 with 4 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) iiiinnnntttt iiiissss____eeeevvvveeeennnn((((iiiinnnnppppuuuutttt)))) iiiinnnntttt iiiinnnnppppuuuutttt CCCCOOOODDDDEEEE:::: RRRREEEETTTTVVVVAAAALLLL ==== ((((iiiinnnnppppuuuutttt %%%% 2222 ======== 0000))));;;; OOOOUUUUTTTTPPPPUUUUTTTT:::: RRRREEEETTTTVVVVAAAALLLL There does not need to be white space at the start of the "int input" line, but it is useful for improving readability. The semi-colon at the end of that line is also optional. Any white space may be between the "int" and "input". It is also okay for the four lines starting at the "CODE:" line to not be indented. However, for readability purposes, it is suggested that you indent them 8 spaces (or one normal tab stop). 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. Remove the line that starts with "use lib", change the print statement in the BEGIN block to print "1..4", and add the following code to the end of the file: pppprrrriiiinnnntttt &&&&MMMMyyyytttteeeesssstttt::::::::iiiissss____eeeevvvveeeennnn((((0000)))) ======== 1111 ???? """"ooookkkk 2222"""" :::: """"nnnnooootttt ooookkkk 2222"""",,,, """"\\\\nnnn"""";;;; pppprrrriiiinnnntttt &&&&MMMMyyyytttteeeesssstttt::::::::iiiissss____eeeevvvveeeennnn((((1111)))) ======== 0000 ???? """"ooookkkk 3333"""" :::: """"nnnnooootttt ooookkkk 3333"""",,,, """"\\\\nnnn"""";;;; pppprrrriiiinnnntttt &&&&MMMMyyyytttteeeesssstttt::::::::iiiissss____eeeevvvveeeennnn((((2222)))) ======== 1111 ???? """"ooookkkk 4444"""" :::: """"nnnnooootttt ooookkkk 4444"""",,,, """"\\\\nnnn"""";;;; We will be calling the test script through the command "make test". You should see output that looks something like this: %%%% mmmmaaaakkkkeeee tttteeeesssstttt PPPPEEEERRRRLLLL____DDDDLLLL____NNNNOOOONNNNLLLLAAAAZZZZYYYY====1111 ////oooopppptttt////ppppeeeerrrrllll5555....000000002222bbbb2222////bbbbiiiinnnn////ppppeeeerrrrllll ((((lllloooottttssss ooooffff ----IIII aaaarrrrgggguuuummmmeeeennnnttttssss)))) tttteeeesssstttt....ppppllll 1111........4444 ooookkkk 1111 ooookkkk 2222 ooookkkk 3333 ooookkkk 4444 %%%% 12/Feb/96 perl 5.002 with 5 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) WWWWHHHHAAAATTTT HHHHAAAASSSS GGGGOOOONNNNEEEE OOOONNNN???? 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 files <extension>.pm and <extension>.xs 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 and invoking the Makefile created a directory blib (which stands for "build library") in the current working directory. This directory will contain the shared library that we will build. Once we have tested it, we can install it into its final location. Invoking the test script via "make test" did something very important. It invoked perl with all those -I arguments so that it could find the various files that are part of the extension. It is _v_e_r_y important that while you are still testing extensions that you use "make test". If you try to run the test script all by itself, you will get a fatal error. Another reason it is important to use "make test" to run your test script is that if you are testing an upgrade to an already-existing version, using "make test" insures that you use your new extension, not the already-existing version. When Perl sees a uuuusssseeee eeeexxxxtttteeeennnnssssiiiioooonnnn;;;;, it searches for a file with the same name as the use'd extension that has a .pm suffix. If that file cannot be found, Perl dies with a fatal error. The default search path is contained in the @@@@IIIINNNNCCCC array. In our case, Mytest.pm tells perl that it will need the Exporter and Dynamic Loader extensions. It then sets the @@@@IIIISSSSAAAA and @@@@EEEEXXXXPPPPOOOORRRRTTTT arrays and the $$$$VVVVEEEERRRRSSSSIIIIOOOONNNN scalar; finally it tells perl to bootstrap the module. Perl will call its dynamic loader routine (if there is one) and load the shared library. The two arrays that are set in the .pm file are very important. The @@@@IIIISSSSAAAA array contains a list of other packages in which to search for methods (or subroutines) 12/Feb/96 perl 5.002 with 6 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) that do not exist in the current package. The @@@@EEEEXXXXPPPPOOOORRRRTTTT array tells Perl which of the extension's routines should be placed into the calling package's namespace. It's important to select what to export carefully. Do NOT export method names and do NOT export anything else _b_y _d_e_f_a_u_l_t without a good reason. As a general rule, if the module is trying to be object- oriented then don't export anything. If it's just a collection of functions then you can export any of the functions via another array, called @@@@EEEEXXXXPPPPOOOORRRRTTTT____OOOOKKKK. See the _p_e_r_l_m_o_d manpage for more information. The $$$$VVVVEEEERRRRSSSSIIIIOOOONNNN variable is used to ensure that the .pm file and the shared library are "in sync" with each other. Any time you make changes to the .pm or .xs files, you should increment the value of this variable. WWWWRRRRIIIITTTTIIIINNNNGGGG GGGGOOOOOOOODDDD TTTTEEEESSSSTTTT SSSSCCCCRRRRIIIIPPPPTTTTSSSS The 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 "make test", you ensure that your test.pl script runs and uses the correct version of your extension. If you have many test cases, you might want to copy Perl's test style. Create a directory named "t", and ensure all your test files end with the suffix ".t". The Makefile will properly run all these test files. EEEEXXXXAAAAMMMMPPPPLLLLEEEE 3333 Our third extension will take one argument as its input, round off that value, and set the _a_r_g_u_m_e_n_t to the rounded value. Add the following to the end of Mytest.xs: 12/Feb/96 perl 5.002 with 7 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) vvvvooooiiiidddd rrrroooouuuunnnndddd((((aaaarrrrgggg)))) ddddoooouuuubbbblllleeee aaaarrrrgggg CCCCOOOODDDDEEEE:::: iiiiffff ((((aaaarrrrgggg >>>> 0000....0000)))) {{{{ aaaarrrrgggg ==== fffflllloooooooorrrr((((aaaarrrrgggg ++++ 0000....5555))));;;; }}}} eeeellllsssseeee iiiiffff ((((aaaarrrrgggg <<<< 0000....0000)))) {{{{ aaaarrrrgggg ==== cccceeeeiiiillll((((aaaarrrrgggg ---- 0000....5555))));;;; }}}} eeeellllsssseeee {{{{ aaaarrrrgggg ==== 0000....0000;;;; }}}} OOOOUUUUTTTTPPPPUUUUTTTT:::: aaaarrrrgggg Edit the Makefile.PL file so that the corresponding line looks like this: ''''LLLLIIIIBBBBSSSS'''' ====>>>> [[[[''''----llllmmmm'''']]]],,,, #### eeee....gggg....,,,, ''''----llllmmmm'''' Generate the Makefile and run make. Change the BEGIN block to print out "1..9" and add the following to test.pl: $$$$iiii ==== ----1111....5555;;;; &&&&MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd(((($$$$iiii))));;;; pppprrrriiiinnnntttt $$$$iiii ======== ----2222....0000 ???? """"ooookkkk 5555"""" :::: """"nnnnooootttt ooookkkk 5555"""",,,, """"\\\\nnnn"""";;;; $$$$iiii ==== ----1111....1111;;;; &&&&MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd(((($$$$iiii))));;;; pppprrrriiiinnnntttt $$$$iiii ======== ----1111....0000 ???? """"ooookkkk 6666"""" :::: """"nnnnooootttt ooookkkk 6666"""",,,, """"\\\\nnnn"""";;;; $$$$iiii ==== 0000....0000;;;; &&&&MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd(((($$$$iiii))));;;; pppprrrriiiinnnntttt $$$$iiii ======== 0000....0000 ???? """"ooookkkk 7777"""" :::: """"nnnnooootttt ooookkkk 7777"""",,,, """"\\\\nnnn"""";;;; $$$$iiii ==== 0000....5555;;;; &&&&MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd(((($$$$iiii))));;;; pppprrrriiiinnnntttt $$$$iiii ======== 1111....0000 ???? """"ooookkkk 8888"""" :::: """"nnnnooootttt ooookkkk 8888"""",,,, """"\\\\nnnn"""";;;; $$$$iiii ==== 1111....2222;;;; &&&&MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd(((($$$$iiii))));;;; pppprrrriiiinnnntttt $$$$iiii ======== 1111....0000 ???? """"ooookkkk 9999"""" :::: """"nnnnooootttt ooookkkk 9999"""",,,, """"\\\\nnnn"""";;;; Running "make test" should now print out that all nine tests are okay. You might be wondering if you can round a constant. To see what happens, add the following line to test.pl temporarily: &&&&MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd((((3333))));;;; Run "make test" and notice that Perl dies with a fatal error. Perl won't let you change the value of constants! WWWWHHHHAAAATTTT''''SSSS NNNNEEEEWWWW HHHHEEEERRRREEEE???? Two things are new here. First, we've made some changes to Makefile.PL. In this case, we've specified an extra library to link in, in this case the math library, libm. We'll talk later about how to write XSUBs that can call every routine in a library. Second, the value of the function is being passed back not as the function's return value, but through the same variable that was passed into the function. 12/Feb/96 perl 5.002 with 8 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) IIIINNNNPPPPUUUUTTTT AAAANNNNDDDD OOOOUUUUTTTTPPPPUUUUTTTT PPPPAAAARRRRAAAAMMMMEEEETTTTEEEERRRRSSSS You specify the parameters that will be passed into the XSUB just after you declare the function return value and name. Each parameter line starts with optional white space, and may have an optional terminating semicolon. The list of output parameters occurs 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, the value we wanted returned was contained in the same variable we passed in, so we listed it (and not RETVAL) in the OUTPUT: section. TTTTHHHHEEEE XXXXSSSSUUUUBBBBPPPPPPPP CCCCOOOOMMMMPPPPIIIILLLLEEEERRRR The compiler xsubpp takes the XS code in the .xs file and converts 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. TTTTHHHHEEEE TTTTYYYYPPPPEEEEMMMMAAAAPPPP FFFFIIIILLLLEEEE The xsubpp compiler 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 part attempts to map various C data types to a coded flag, which has some correspondence with the various Perl types. The second part contains C code which xsubpp uses for input parameters. The third part contains C code which xsubpp uses for output parameters. We'll talk more about the C code later. Let's now take a look at a portion of the .c file created for our extension. 12/Feb/96 perl 5.002 with 9 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) XXXXSSSS((((XXXXSSSS____MMMMyyyytttteeeesssstttt____rrrroooouuuunnnndddd)))) {{{{ ddddXXXXSSSSAAAARRRRGGGGSSSS;;;; iiiiffff ((((iiiitttteeeemmmmssss !!!!==== 1111)))) ccccrrrrooooaaaakkkk((((""""UUUUssssaaaaggggeeee:::: MMMMyyyytttteeeesssstttt::::::::rrrroooouuuunnnndddd((((aaaarrrrgggg))))""""))));;;; {{{{ ddddoooouuuubbbblllleeee aaaarrrrgggg ==== ((((ddddoooouuuubbbblllleeee))))SSSSvvvvNNNNVVVV((((SSSSTTTT((((0000))))))));;;; ////**** XXXXXXXXXXXXXXXXXXXX ****//// iiiiffff ((((aaaarrrrgggg >>>> 0000....0000)))) {{{{ aaaarrrrgggg ==== fffflllloooooooorrrr((((aaaarrrrgggg ++++ 0000....5555))));;;; }}}} eeeellllsssseeee iiiiffff ((((aaaarrrrgggg <<<< 0000....0000)))) {{{{ aaaarrrrgggg ==== cccceeeeiiiillll((((aaaarrrrgggg ---- 0000....5555))));;;; }}}} eeeellllsssseeee {{{{ aaaarrrrgggg ==== 0000....0000;;;; }}}} ssssvvvv____sssseeeettttnnnnvvvv((((SSSSTTTT((((0000)))),,,, ((((ddddoooouuuubbbblllleeee))))aaaarrrrgggg))));;;; ////**** XXXXXXXXXXXXXXXXXXXX ****//// }}}} XXXXSSSSRRRREEEETTTTUUUURRRRNNNN((((1111))));;;; }}}} Notice the two lines marked 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 _p_e_r_l_g_u_t_s manpage; we'll talk more later about what that "_S_T(0)" means in the section on the argument stack. WWWWAAAARRRRNNNNIIIINNNNGGGG In general, it's not a good idea to write extensions that modify their input parameters, as in Example 3. However, in order to better accomodate calling pre-existing C routines, which often do modify their input parameters, this behavior is tolerated. EEEEXXXXAAAAMMMMPPPPLLLLEEEE 4444 In this example, we'll now begin to write XSUB's 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. 12/Feb/96 perl 5.002 with 10 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) 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 testlib directory, create a file mylib.h that looks like this: ####ddddeeeeffffiiiinnnneeee TTTTEEEESSSSTTTTVVVVAAAALLLL 4444 eeeexxxxtttteeeerrrrnnnn ddddoooouuuubbbblllleeee ffffoooooooo((((iiiinnnntttt,,,, lllloooonnnngggg,,,, ccccoooonnnnsssstttt cccchhhhaaaarrrr****))));;;; Also create a file mylib.c that looks like this: ####iiiinnnncccclllluuuuddddeeee <<<<ssssttttddddlllliiiibbbb....hhhh>>>> ####iiiinnnncccclllluuuuddddeeee """"....////mmmmyyyylllliiiibbbb....hhhh"""" ddddoooouuuubbbblllleeee ffffoooooooo((((aaaa,,,, bbbb,,,, cccc)))) iiiinnnntttt aaaa;;;; lllloooonnnngggg bbbb;;;; ccccoooonnnnsssstttt cccchhhhaaaarrrr **** cccc;;;; {{{{ rrrreeeettttuuuurrrrnnnn ((((aaaa ++++ bbbb ++++ aaaattttooooffff((((cccc)))) ++++ TTTTEEEESSSSTTTTVVVVAAAALLLL))));;;; }}}} And finally create a file Makefile.PL that looks like this: uuuusssseeee EEEExxxxttttUUUUttttiiiillllssss::::::::MMMMaaaakkkkeeeeMMMMaaaakkkkeeeerrrr;;;; $$$$VVVVeeeerrrrbbbboooosssseeee ==== 1111;;;; WWWWrrrriiiitttteeeeMMMMaaaakkkkeeeeffffiiiilllleeee(((( ''''NNNNAAAAMMMMEEEE'''' ====>>>> ''''MMMMyyyytttteeeesssstttt2222::::::::mmmmyyyylllliiiibbbb'''',,,, ''''cccclllleeeeaaaannnn'''' ====>>>> {{{{''''FFFFIIIILLLLEEEESSSS'''' ====>>>> ''''lllliiiibbbbmmmmyyyylllliiiibbbb....aaaa''''}}}},,,, ))));;;; ssssuuuubbbb MMMMYYYY::::::::ppppoooossssttttaaaammmmbbbblllleeee {{{{ '''' aaaallllllll :::::::: ssssttttaaaattttiiiicccc ssssttttaaaattttiiiicccc :::::::: lllliiiibbbbmmmmyyyylllliiiibbbb$$$$((((LLLLIIIIBBBB____EEEEXXXXTTTT)))) lllliiiibbbbmmmmyyyylllliiiibbbb$$$$((((LLLLIIIIBBBB____EEEEXXXXTTTT)))):::: $$$$((((OOOO____FFFFIIIILLLLEEEESSSS)))) $$$$((((AAAARRRR)))) ccccrrrr lllliiiibbbbmmmmyyyylllliiiibbbb$$$$((((LLLLIIIIBBBB____EEEEXXXXTTTT)))) $$$$((((OOOO____FFFFIIIILLLLEEEESSSS)))) $$$$((((RRRRAAAANNNNLLLLIIIIBBBB)))) lllliiiibbbbmmmmyyyylllliiiibbbb$$$$((((LLLLIIIIBBBB____EEEEXXXXTTTT)))) '''';;;; }}}} We will now create the main top-level Mytest2 files. Change to the directory above Mytest2 and run the following command: %%%% hhhh2222xxxxssss ----OOOO ----nnnn MMMMyyyytttteeeesssstttt2222 <<<< ....////MMMMyyyytttteeeesssstttt2222////mmmmyyyylllliiiibbbb////mmmmyyyylllliiiibbbb....hhhh 12/Feb/96 perl 5.002 with 11 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) This will print out a warning about overwriting Mytest2, but that's okay. Our files are stored in Mytest2/mylib, and will be untouched. The normal Makefile.PL that h2xs generates doesn't know about the mylib directory. We need to tell it that there is a subdirectory and that we will be generating a library in it. Let's add the following key-value pair to the WriteMakefile call: ''''MMMMYYYYEEEEXXXXTTTTLLLLIIIIBBBB'''' ====>>>> ''''mmmmyyyylllliiiibbbb////lllliiiibbbbmmmmyyyylllliiiibbbb$$$$((((LLLLIIIIBBBB____EEEEXXXXTTTT))))'''',,,, and a new replacement subroutine too: ssssuuuubbbb MMMMYYYY::::::::ppppoooossssttttaaaammmmbbbblllleeee {{{{ '''' $$$$((((MMMMYYYYEEEEXXXXTTTTLLLLIIIIBBBB)))):::: mmmmyyyylllliiiibbbb////MMMMaaaakkkkeeeeffffiiiilllleeee ccccdddd mmmmyyyylllliiiibbbb &&&&&&&& $$$$((((MMMMAAAAKKKKEEEE)))) '''';;;; }}}} (Note: Most makes will require that there be a tab character that indents the line "cd mylib && $(MAKE)".) 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: mmmmyyyylllliiiibbbb////MMMMaaaakkkkeeeeffffiiiilllleeee....PPPPLLLL mmmmyyyylllliiiibbbb////mmmmyyyylllliiiibbbb....cccc mmmmyyyylllliiiibbbb////mmmmyyyylllliiiibbbb....hhhh To keep our namespace nice and unpolluted, edit the .pm file and change the line setting @@@@EEEEXXXXPPPPOOOORRRRTTTT to @@@@EEEEXXXXPPPPOOOORRRRTTTT____OOOOKKKK. And finally, in the .xs file, edit the #include line to read: ####iiiinnnncccclllluuuuddddeeee """"mmmmyyyylllliiiibbbb////mmmmyyyylllliiiibbbb....hhhh"""" And also add the following function definition to the end of the .xs file: ddddoooouuuubbbblllleeee ffffoooooooo((((aaaa,,,,bbbb,,,,cccc)))) iiiinnnntttt aaaa lllloooonnnngggg bbbb ccccoooonnnnsssstttt cccchhhhaaaarrrr **** cccc OOOOUUUUTTTTPPPPUUUUTTTT:::: RRRREEEETTTTVVVVAAAALLLL 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 and place the 12/Feb/96 perl 5.002 with 12 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) following in it: ccccoooonnnnsssstttt cccchhhhaaaarrrr **** TTTT____PPPPVVVV Now run perl on the top-level Makefile.PL. Notice that it also created a Makefile in the mylib directory. Run make and see 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: pppprrrriiiinnnntttt &&&&MMMMyyyytttteeeesssstttt2222::::::::ffffoooooooo((((1111,,,, 2222,,,, """"HHHHeeeelllllllloooo,,,, wwwwoooorrrrlllldddd!!!!"""")))) ======== 7777 ???? """"ooookkkk 2222\\\\nnnn"""" :::: """"nnnnooootttt ooookkkk 2222\\\\nnnn"""";;;; pppprrrriiiinnnntttt &&&&MMMMyyyytttteeeesssstttt2222::::::::ffffoooooooo((((1111,,,, 2222,,,, """"0000....0000"""")))) ======== 7777 ???? """"ooookkkk 3333\\\\nnnn"""" :::: """"nnnnooootttt ooookkkk 3333\\\\nnnn"""";;;; pppprrrriiiinnnntttt aaaabbbbssss((((&&&&MMMMyyyytttteeeesssstttt2222::::::::ffffoooooooo((((0000,,,, 0000,,,, """"----3333....4444"""")))) ---- 0000....6666)))) <<<<==== 0000....00001111 ???? """"ooookkkk 4444\\\\nnnn"""" :::: """"nnnnooootttt ooookkkk 4444\\\\nnnn"""";;;; (When dealing with floating-point comparisons, it is often useful to not check for equality, but rather the difference being below a certain epsilon factor, 0.01 in this case) Run "make test" and all should be well. 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. +o In the .xs file, there's now a #include declaration with the full path to the mylib.h header file. +o There's now some new C code that's been added to the .xs file. The purpose of the ccccoooonnnnssssttttaaaannnntttt routine is to make the values that are #define'd in the header file available to the Perl script (in this case, by calling &&&&mmmmaaaaiiiinnnn::::::::TTTTEEEESSSSTTTTVVVVAAAALLLL). There's also some XS code to allow calls to the ccccoooonnnnssssttttaaaannnntttt routine. +o The .pm file has exported the name TESTVAL in the @@@@EEEEXXXXPPPPOOOORRRRTTTT array. This could lead to name clashes. A good rule of thumb is that if the #define is only going to be used by the C routines themselves, and not by the user, they should be removed from the @@@@EEEEXXXXPPPPOOOORRRRTTTT array. Alternately, if you don't mind using the "fully qualified name" of a variable, you could remove most or all of the items in the @@@@EEEEXXXXPPPPOOOORRRRTTTT array. We've also told Perl about the library that we built in the mylib subdirectory. That required only the addition of the MYEXTLIB variable to the WriteMakefile call and the replacement of the postamble subroutine to cd into the subdirectory and run make. The Makefile.PL for the 12/Feb/96 perl 5.002 with 13 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) library is a bit more complicated, but not excessively so. Again we replaced the postamble subroutine to insert our own code. This code simply specified that the library to be created here was a static archive (as opposed to a dynamically loadable library) and provided the commands to build it. SSSSPPPPEEEECCCCIIIIFFFFYYYYIIIINNNNGGGG AAAARRRRGGGGUUUUMMMMEEEENNNNTTTTSSSS TTTTOOOO XXXXSSSSUUUUBBBBPPPPPPPP With 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 in the .xs file, you are really passing three pieces of information for each one 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 exact way in which the argument should be used in the call to the library function from this XSUB. This would mean whether or not to place a "&" before the argument or not, meaning the argument expects to be passed the address of the specified data type. There is a difference between the two arguments in this hypothetical function: iiiinnnntttt ffffoooooooo((((aaaa,,,,bbbb)))) cccchhhhaaaarrrr &&&&aaaa cccchhhhaaaarrrr **** bbbb The first 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 argument would be treated as a string pointer and assigned to the variable b. The _v_a_l_u_e of b would be passed into the function foo. The actual call to the function foo that xsubpp generates would look like this: ffffoooooooo((((&&&&aaaa,,,, bbbb))));;;; Xsubpp will identically parse the following function argument lists: cccchhhhaaaarrrr &&&&aaaa cccchhhhaaaarrrr&&&&aaaa cccchhhhaaaarrrr &&&& aaaa However, to help ease understanding, it is suggested that you place a "&" next to the variable name and away from 12/Feb/96 perl 5.002 with 14 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) the variable type), and place a "*" near the variable type, but away from the variable name (as in the complete example 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. TTTTHHHHEEEE AAAARRRRGGGGUUUUMMMMEEEENNNNTTTT SSSSTTTTAAAACCCCKKKK If 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 _S_T(n), where n is usually 0. The "ST" is actually a macro that points to the n'th argument on the argument stack. _S_T(0) is thus the first argument passed to the XSUB, _S_T(1) is the second argument, and so on. When you list the arguments to the XSUB in the .xs file, that tell 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. EEEEXXXXTTTTEEEENNNNDDDDIIIINNNNGGGG YYYYOOOOUUUURRRR EEEEXXXXTTTTEEEENNNNSSSSIIIIOOOONNNN Sometimes 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. DDDDOOOOCCCCUUUUMMMMEEEENNNNTTTTIIIINNNNGGGG YYYYOOOOUUUURRRR EEEEXXXXTTTTEEEENNNNSSSSIIIIOOOONNNN There 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 _p_e_r_l_p_o_d manpage for more information about the pod format. 12/Feb/96 perl 5.002 with 15 PERLXSTUT(1) User Contributed Perl Documentation PERLXSTUT(1) IIIINNNNSSSSTTTTAAAALLLLLLLLIIIINNNNGGGG YYYYOOOOUUUURRRR EEEEXXXXTTTTEEEENNNNSSSSIIIIOOOONNNN Once 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. SSSSEEEEEEEE AAAALLLLSSSSOOOO For more information, consult the _p_e_r_l_g_u_t_s manpage, the _p_e_r_l_x_s manpage, the _p_e_r_l_m_o_d manpage, and the _p_e_r_l_p_o_d manpage. AAAAuuuutttthhhhoooorrrr Jeff Okamoto <okamoto@corp.hp.com> Reviewed and assisted by Dean Roehrich, Ilya Zakharevich, Andreas Koenig, and Tim Bunce. LLLLaaaasssstttt CCCChhhhaaaannnnggggeeeedddd 1996/2/9 12/Feb/96 perl 5.002 with 16