Re: VPATH/vpath: does it work for -l<libname> prereqs?

[John Graham-Cumming]

Matt England wrote:
> VPATH/vpath: does it work for -l<libname> prereqs?

Yes, but there's special handling of this syntax detailed in the GNU 
Make manual section "Directory Search for Link Libraries" and I quote:

  "When a prerequisite's name has the form `-lNAME', `make' handles it
  specially by searching for the file `libNAME.so' in the current
  directory, in directories specified by matching `vpath' search paths
  and the `VPATH' search path, and then in the directories `/lib',
  `/usr/lib', and `PREFIX/lib' (normally `/usr/local/lib', but
  MS-DOS/MS-Windows versions of `make' behave as if PREFIX is defined to
  be the root of the DJGPP installation tree).

   If that file is not found, then the file `libNAME.a' is searched
  for, in the same directories as above."

You might like to post a snippet of Makefile so that people here can 
help you debug.  Here's a sample that does work:

    all: my_executable

    my_executable: -lm
        link_it $@ $^

(Run with -n since link_it isn't a real program :-)

    % make -n
    link_it my_executable /usr/lib/libm.so

Now suppose there's a libm.so in the current directory you'll see:

    % make -n
    link_it my_executable /usr/lib/libm.so

Or suppose there's a libm.so in ./subdir and you do

    % make -n VPATH=./subdir
    link_it my_executable ./subdir/libm.so

Or even add 'vpath %.so ./subdir' to the Makefile:

    % make -n
    link_it my_executable ./subdir/libm.so

Now one thing to watch for is if your library is a .a and has the same 
name as a .so the search order used by GNU Make (see above) will cause 
the .so to be found and used first.  If that's a problem then you can 
either stop using the -l syntax, or you can fiddle with .LIBPATTERNS so 
that the search happens in the opposite order.

John.
--
John Graham-Cumming
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