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ExtUtils::LiblistPerl Programmers Reference ExtUtils::Liblist(3p)


NAME
       ExtUtils::Liblist - determine libraries to use and how to
       use them

SYNOPSIS
         require ExtUtils::Liblist;

         $MM->ext($potential_libs, $verbose, $need_names);

         # Usually you can get away with:
         ExtUtils::Liblist->ext($potential_libs, $verbose, $need_names)

DESCRIPTION
       This utility takes a list of libraries in the form "-llib1
       -llib2 -llib3" and returns lines suitable for inclusion in
       an extension Makefile.  Extra library paths may be
       included with the form "-L/another/path" this will affect
       the searches for all subsequent libraries.

       It returns an array of four or five scalar values: EXTRAL-
       IBS, BSLOADLIBS, LDLOADLIBS, LD_RUN_PATH, and, optionally,
       a reference to the array of the filenames of actual
       libraries.  Some of these don't mean anything unless on
       Unix.  See the details about those platform specifics
       below.  The list of the filenames is returned only if
       $need_names argument is true.

       Dependent libraries can be linked in one of three ways:

       * For static extensions
         by the ld command when the perl binary is linked with
         the extension library. See EXTRALIBS below.

       * For dynamic extensions at build/link time
         by the ld command when the shared object is
         built/linked. See LDLOADLIBS below.

       * For dynamic extensions at load time
         by the DynaLoader when the shared object is loaded. See
         BSLOADLIBS below.

       EXTRALIBS

       List of libraries that need to be linked with when linking
       a perl binary which includes this extension. Only those
       libraries that actually exist are included.  These are
       written to a file and used when linking perl.

       LDLOADLIBS and LD_RUN_PATH

       List of those libraries which can or must be linked into
       the shared library when created using ld. These may be
       static or dynamic libraries.  LD_RUN_PATH is a colon sepa-
       rated list of the directories in LDLOADLIBS. It is passed



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       as an environment variable to the process that links the
       shared library.

       BSLOADLIBS

       List of those libraries that are needed but can be linked
       in dynamically at run time on this platform.
       SunOS/Solaris does not need this because ld records the
       information (from LDLOADLIBS) into the object file.  This
       list is used to create a .bs (bootstrap) file.

PORTABILITY
       This module deals with a lot of system dependencies and
       has quite a few architecture specific "if"s in the code.

       VMS implementation

       The version of ext() which is executed under VMS differs
       from the Unix-OS/2 version in several respects:

       o Input library and path specifications are accepted with
         or without the "-l" and "-L" prefixes used by Unix link-
         ers.  If neither prefix is present, a token is consid-
         ered a directory to search if it is in fact a directory,
         and a library to search for otherwise.  Authors who wish
         their extensions to be portable to Unix or OS/2 should
         use the Unix prefixes, since the Unix-OS/2 version of
         ext() requires them.

       o Wherever possible, shareable images are preferred to
         object libraries, and object libraries to plain object
         files.  In accordance with VMS naming conventions, ext()
         looks for files named libshr and librtl; it also looks
         for liblib and liblib to accommodate Unix conventions
         used in some ported software.

       o For each library that is found, an appropriate directive
         for a linker options file is generated.  The return val-
         ues are space-separated strings of these directives,
         rather than elements used on the linker command line.

       o LDLOADLIBS contains both the libraries found based on
         $potential_libs and the CRTLs, if any, specified in Con-
         fig.pm.  EXTRALIBS contains just those libraries found
         based on $potential_libs.  BSLOADLIBS and LD_RUN_PATH
         are always empty.

       In addition, an attempt is made to recognize several com-
       mon Unix library names, and filter them out or convert
       them to their VMS equivalents, as appropriate.

       In general, the VMS version of ext() should properly han-
       dle input from extensions originally designed for a Unix
       or VMS environment.  If you encounter problems, or



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       discover cases where the search could be improved, please
       let us know.

       Win32 implementation

       The version of ext() which is executed under Win32 differs
       from the Unix-OS/2 version in several respects:

       o If $potential_libs is empty, the return value will be
         empty.  Otherwise, the libraries specified by $Con-
         fig{perllibs} (see Config.pm) will be appended to the
         list of $potential_libs.  The libraries will be searched
         for in the directories specified in $potential_libs,
         $Config{libpth}, and in "$Config{installarchlib}/CORE".
         For each library that is found,  a space-separated list
         of fully qualified library pathnames is generated.

       o Input library and path specifications are accepted with
         or without the "-l" and "-L" prefixes used by Unix link-
         ers.

         An entry of the form "-La:\foo" specifies the "a:\foo"
         directory to look for the libraries that follow.

         An entry of the form "-lfoo" specifies the library
         "foo", which may be spelled differently depending on
         what kind of compiler you are using.  If you are using
         GCC, it gets translated to "libfoo.a", but for other
         win32 compilers, it becomes "foo.lib".  If no files are
         found by those translated names, one more attempt is
         made to find them using either "foo.a" or "libfoo.lib",
         depending on whether GCC or some other win32 compiler is
         being used, respectively.

         If neither the "-L" or "-l" prefix is present in an
         entry, the entry is considered a directory to search if
         it is in fact a directory, and a library to search for
         otherwise.  The $Config{lib_ext} suffix will be appended
         to any entries that are not directories and don't
         already have the suffix.

         Note that the "-L" and "-l" prefixes are not required,
         but authors who wish their extensions to be portable to
         Unix or OS/2 should use the prefixes, since the
         Unix-OS/2 version of ext() requires them.

       o Entries cannot be plain object files, as many Win32 com-
         pilers will not handle object files in the place of
         libraries.

       o Entries in $potential_libs beginning with a colon and
         followed by alphanumeric characters are treated as
         flags.  Unknown flags will be ignored.




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         An entry that matches "/:nodefault/i" disables the
         appending of default libraries found in $Config{perl-
         libs} (this should be only needed very rarely).

         An entry that matches "/:nosearch/i" disables all
         searching for the libraries specified after it.  Trans-
         lation of "-Lfoo" and "-lfoo" still happens as appropri-
         ate (depending on compiler being used, as reflected by
         $Config{cc}), but the entries are not verified to be
         valid files or directories.

         An entry that matches "/:search/i" reenables searching
         for the libraries specified after it.  You can put it at
         the end to enable searching for default libraries speci-
         fied by $Config{perllibs}.

       o The libraries specified may be a mixture of static
         libraries and import libraries (to link with DLLs).
         Since both kinds are used pretty transparently on the
         Win32 platform, we do not attempt to distinguish between
         them.

       o LDLOADLIBS and EXTRALIBS are always identical under
         Win32, and BSLOADLIBS and LD_RUN_PATH are always empty
         (this may change in future).

       o You must make sure that any paths and path components
         are properly surrounded with double-quotes if they con-
         tain spaces. For example, $potential_libs could be (lit-
         erally):

                 "-Lc:\Program Files\vc\lib" msvcrt.lib "la test\foo bar.lib"

         Note how the first and last entries are protected by
         quotes in order to protect the spaces.

       o Since this module is most often used only indirectly
         from extension "Makefile.PL" files, here is an example
         "Makefile.PL" entry to add a library to the build pro-
         cess for an extension:

                 LIBS => ['-lgl']

         When using GCC, that entry specifies that MakeMaker
         should first look for "libgl.a" (followed by "gl.a") in
         all the locations specified by $Config{libpth}.

         When using a compiler other than GCC, the above entry
         will search for "gl.lib" (followed by "libgl.lib").

         If the library happens to be in a location not in $Con-
         fig{libpth}, you need:

                 LIBS => ['-Lc:\gllibs -lgl']



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         Here is a less often used example:

                 LIBS => ['-lgl', ':nosearch -Ld:\mesalibs -lmesa -luser32']

         This specifies a search for library "gl" as before.  If
         that search fails to find the library, it looks at the
         next item in the list. The ":nosearch" flag will prevent
         searching for the libraries that follow, so it simply
         returns the value as "-Ld:\mesalibs -lmesa -luser32",
         since GCC can use that value as is with its linker.

         When using the Visual C compiler, the second item is
         returned as "-libpath:d:\mesalibs mesa.lib user32.lib".

         When using the Borland compiler, the second item is
         returned as "-Ld:\mesalibs mesa.lib user32.lib", and
         MakeMaker takes care of moving the "-Ld:\mesalibs" to
         the correct place in the linker command line.

SEE ALSO
       ExtUtils::MakeMaker




































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