Help Files: Fortran77: User Libraries

     HELP                      Sep. 15, 1984              F77/USERLIBS



                 Making Random Libraries from Object Files

     A library is a single file which contains many  different  object
     files plus an index to the contents of the library.  In UNIX, li-
     braries are "archives" and have names ending in ".a".  When load-
     ing,  only the needed object files are loaded from libraries men-
     tioned in the f77 command.  To load a  program  requiring  object
     files from library file "mylib.a" in the current directory, type:

             f77 prog.o sub1.o ... mylib.a

     This loads the object files prog.o, sub1.o, etc. and  then  loads
     those object files in mylib.a that prog.o, sub1.o, ... reference.

     Library names are listed at the end of the  f77  command  because
     object files in the libraries are loaded only if the object files
     are referenced by previously loaded object files.

     The "ar" command creates and maintains archives on UNIX.  Here is
     a simple example that compiles three subroutines and adds them to
     the archive mylib.a:

             f77 -c sub1.f sub2.f sub3.f
             ar uv mylib.a  sub1.o sub2.o sub3.o

     Ar will respond with "a - sub.o" when a file  is  first  inserted
     (appended) into the archive.  We could use the same ar command to
     replace  already  existing  object  files  in  the  archive.   Ar
     responds  with  "r  - sub.o" when a file is updated (replaced) in
     the archive.

     Use ranlib to add a random table of contents to the archive, con-
     verting it to a library:

             ranlib mylib.a

     To see what .o files are in a library or archive, type:

             ar tv mylib.a

     To see what subprograms, entry  points,  and  common  blocks  are
     referenced by the .o files in an archive, type:

             nm -g mylib.a

     The loader checks whether the random index of a library is up  to
     date  or not by comparing the date within the file to the modifi-
     cation date of the file.  Because of this, if you  use  the  'cp'
     command to make a second copy of a library, the loader thinks the
     random index for the library is out of date, ignores it  and  is-
     sues a warning:

             % cp  libnew.a  mylib.a
             % f77  prog.o  mylib.a
             ld:mylib.a: warning: table of contents for archive is out
                of date; rerun ranlib(1)

     Instead, either use the 'mv' command if you just want  to  change
     the  name or path of the library, or use the 'tar' command if you
     really want to make an identical copy.  To use 'tar', first  move
     into  the  directory containing the library.  Then issue the com-
     mand:

             tar cBf - libnew.a | ( cd ~/newdir ; tar xBf - libnew.a )

     This copies libnew.a to ~/newdir/libnew.a.  Tar creates  the  new
     file with the same modification date as the original file so that
     you do not need to rerun ranlib.  Notice that the name of the li-
     brary,  libnew.a,  appears  twice in the command line and must be
     identical in both positions.  If you want the copy of the library
     to have a different name, follow the tar with a mv command.

     To copy a library across systems, use tar together with rsh; e.g.
     to  copy  mylib.a  on opal to ~/mybin/mylib.a on populi, type the
     following on opal:

             tar cBf - mylib.a \
                      | rsh populi "( cd mybin; tar xBf - mylib.a )"

     For large  libraries,  you  may  want  to  check  if  there  were
     transmission errors by comparing the copy to the original:

             rsh populi cat mylib.a | cmp - mylib.a

     For more information, see ar(1),  ld(1),  nm(1),  ranlib(1),  and
     rsh(1) in the UNIX Programmer's Manual.

     For information of importance in dealing  with  large  libraries,
     see "help f77 biglibs".