Question

It is possible that more than one instance of the library exists in the search path during compilation. In what order will linker process directories included in the search path? The platform in question is Sun OS.

Answer 1

The directories are searched in the order in which they are specified on the command line. Directories specified on the command line are searched before the default directories. All -L options apply to all -l options, regardless of the order in which the options appear. LD_LIBRARY_PATH may also be used to supplement the library search path. The directory search stops at the first directory containing the matching library.

LD_LIBRARY_PATH is tricky though:

LD_LIBRARY_PATH 

A list of directories in which to search for libraries specified with
the -l option. Multiple directories
are separated by a colon. In the most
general case, it will contain two
directory lists separated by a
semicolon:

dirlist1; dirlist2 

If ld is called with any number of occurrences of -L, as in:

ld . . . -Lpath1 . . . -Lpathn . . .

then the search path ordering is:

         dirlist1 path1 . . . pathn dirlist2 LIBPATH

When the list of directories does not contain a semicolon, it is
interpreted as dirlist2.

LD_LIBRARY_PATH is also used to specify library search directories to
the runtime linker. That is, if
LD_LIBRARY_PATH exists in the
environment, the runtime linker will
search the directories named in it,
before its default directory, for
shared objects to be linked with the
program at execution.

Please read more about it here.