ExtUtils::Liblist(3)

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

SYNOPSIS
     require ExtUtils::Liblist;

     ExtUtils::Liblist::ext($self, $potential_libs, $verbose);

DESCRIPTION
     This utility takes a list of libraries in the form -llib1 -llib2 -llib3
     and prints out 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 scalar values: EXTRALIBS, BSLOADLIBS,
     LDLOADLIBS, and LD_RUN_PATH.  Some of these don't mean anything on VMS
     and Win32.  See the details about those platform specifics below.

     Dependent libraries can be linked in one of three ways:

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

     o For dynamic extensions
       by the ld command when the shared object is built/linked. See
       LDLOADLIBS below.

     o For dynamic extensions
       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 separated list of the directories in LDLOADLIBS.
     It is passed 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 ifs 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 prefices used by Unix linkers.  If neither prefix is present,
       a token is considered 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 accomodate 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 values are space-separated
       strings of these directives, rather than elements used on the linker
       command line.

     o LDLOADLIBS and EXTRALIBS are always identical under VMS, and BSLOADLIBS
       and LD_RIN_PATH are always empty.

     In addition, an attempt is made to recognize several common 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 handle input from
     extensions originally designed for a Unix or VMS environment.  If you
     encounter problems, or 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 $Config{libs} (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 as well as
       in $Config{libpth}. 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 prefices used by Unix linkers.

       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 compilers 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.

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

       An entry that matches /:nosearch/i disables all searching for the
       libraries specified after it.  Translation of -Lfoo and -lfoo still
       happens as appropriate (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 specified by $Config{libs}.

     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 contain spaces. For example,
       $potential_libs could be (literally):

               "-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 process 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 $Config{libpth}, you
       need:

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

       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
     the ExtUtils::MakeMaker manpage