is there a better way to solve this problem: building a library with code from another directory?

[Ed Hartnett]

Howdy all!

In working on the freeware netCDF package (used by meteorologists and
Earth scientists), I have a bit of a challenge.

Depending on a configure time decision by the user, I build my library
in one of two ways. If I configure with --enable-netcdf-4, then I
build the old library as a noinst, and then go to another directory
and build a library that includes .o files from another directory. I
do it like this:

# This is the directory where the netcdf-3 object files are.
NC3_DIR = $(top_srcdir)/libsrc

# Netcdf-4 source.
libnetcdf_a_SOURCES = nc4attr.c nc4internal.c nc4var.c netcdf3.h        \
nc4dim.c nc4internal.h ncfunc.c netcdf4.h nc4file.c netcdf.h nc4hdf.c   \
error.c error.h nc4internal.h nclibstruct.h netcdf3.h netcdf.h          \
nc4grp.c

# Netcdf-3 object files.
libnetcdf_a_LIBADD = $(NC3_DIR)/attr.o $(NC3_DIR)/dim.o \
$(NC3_DIR)/error.o $(NC3_DIR)/libvers.o $(NC3_DIR)/nc.o \
$(NC3_DIR)/ncio.o $(NC3_DIR)/ncx.o $(NC3_DIR)/putget.o  \
$(NC3_DIR)/string.o $(NC3_DIR)/v1hpg.o $(NC3_DIR)/v2i.o \
$(NC3_DIR)/var.o $(NC3_DIR)/v2i.o

# The netcdf-3 objects have to be explictly added as depedencies to
# trigger recompile of netcdf-4 libnetcdf.a if netcdf-3 code changes.
libnetcdf_a_DEPENDENCIES = $(NC3_DIR)/attr.o $(NC3_DIR)/dim.o   \
$(NC3_DIR)/error.o $(NC3_DIR)/libvers.o $(NC3_DIR)/nc.o         \
$(NC3_DIR)/ncio.o $(NC3_DIR)/ncx.o $(NC3_DIR)/putget.o          \
$(NC3_DIR)/string.o $(NC3_DIR)/v1hpg.o $(NC3_DIR)/v2i.o         \
$(NC3_DIR)/var.o $(NC3_DIR)/v2i.o


Is there a better way to do this? Ideally, I would just like to be
able to specify a .c file in another directory as part of the
library. For example, something like this:

linnetcdf_a_SOURCES = nc4attr.c $(NC3_DIR)/attr.c 

But then I try that, I get errors during the build relating to the
automatic dependency tracking.

Is there a good solution to this problem?

Thanks!

Ed 

-- 
Ed Hartnett  -- address@hidden