Confusion with Makefile linking a library that seems to link but I can't call

Question

I am trying yo build a Makefile for a project that uses the soplex library (which also depends on libz and libgmp). So I have this little Makefile:

SOPLEXPATH =../../lib/soplex-3.0.0/lib/
SOPLEXINCLUDE =../../lib/soplex-3.0.0/src/
SOPLEXDEP =../../lib/soplex-3.0.0/src/

CC = g++
CPPFLAGS = -g -std=c++0x -O3 -I $(SOPLEXINCLUDE)
#CPPFLAGS += -DNDEBUG
CPPFLAGS += -pg -ggdb
CPPFLAGS += -Wall -Werror=return-type

LIBS = -L $(SOPLEXPATH) -lz -lgmp -lsoplex 

SRCS = $(wildcard ./src/core/*.cpp) 
OBJS = $(addsuffix .o, $(basename $(SRCS)))
DEPS = $(addsuffix .d, $(basename $(SRCS)))

all : kea

kea : $(OBJS)
    $(CC) $(CPPFLAGS) $(LIBS) -o bin/kea-core $(OBJS)

clean :
    rm -f bin/kea-core $(OBJS) $(DEPS) *~

-include $(DEPS)

%.d: %.c
    @$(CC) -MM -MT  $(subst .d,.o,$@) -MT $@ $(CPPFLAGS) $< > $@

And all seems to compile to object files (.o) correctly, but then the linker complains about not finding the function soplex::SoPlex::SoPlex() (the constructor of SoPlex):

g++  -g -std=c++0x -O3 -I ../../lib/soplex-3.0.0/src/ -pg -ggdb -Wall -Werror=return-type  -c -o src/core/ecircuit.o src/core/ecircuit.cpp
g++  -g -std=c++0x -O3 -I ../../lib/soplex-3.0.0/src/ -pg -ggdb -Wall -Werror=return-type  -c -o src/core/solver_soplex.o src/core/solver_soplex.cpp
g++  -g -std=c++0x -O3 -I ../../lib/soplex-3.0.0/src/ -pg -ggdb -Wall -Werror=return-type  -c -o src/core/main.o src/core/main.cpp
g++ -g -std=c++0x -O3 -I ../../lib/soplex-3.0.0/src/ -pg -ggdb -Wall -Werror=return-type -L ../../lib/soplex-3.0.0/lib/ -lz -lgmp -lsoplex  -o bin/kea-core ./src/core/ecircuit.o ./src/core/solver_soplex.o ./src/core/main.o
./src/core/solver_soplex.o: In function `SolvSoplex::SolvSoplex(ECircuit&, std::vector<std::pair<int, int>, std::allocator<std::pair<int, int> > >&, SolvSoplex::Mode)':
/home/diego/Projects/kea-landscape-tool/src/core/solver_soplex.cpp:9: undefined reference to `soplex::SoPlex::SoPlex()'
/home/diego/Projects/kea-landscape-tool/src/core/solver_soplex.cpp:9: undefined reference to `soplex::SoPlex::~SoPlex()'
collect2: error: ld returned 1 exit status
Makefile:20: recipe for target 'kea' failed
make: *** [kea] Error 1

Since all the .o files are created I tried to compile by hand doing: g++ -g -std=c++0x -O3 -I ../../lib/soplex-3.0.0/src/ -Wall -Werror=return-type -pg -ggdb -L/home/diego/Projects/kea-landscape-tool/../../lib/soplex-3.0.0/lib/ -lsoplex -lz -lgmp -o bin/kea-core src/core/main.o src/core/ecircuit.o src/core/solver_soplex.o And it failed with the same error.

then I tried switching the position of the -L and -l.. flags like this, and it compiled: g++ -g -std=c++0x -O3 -I ../../lib/soplex-3.0.0/src/ -Wall -Werror=return-type -pg -ggdb -o bin/kea-core src/core/main.o src/core/ecircuit.o src/core/solver_soplex.o -L/home/diego/Projects/kea-landscape-tool/../../lib/soplex-3.0.0/lib/ -lsoplex -lz -lgmp

Seeing that, I tried to change the rule in the Makefile as follows:

kea : $(OBJS)
    $(CC) $(CPPFLAGS) -o bin/kea-core $(OBJS) $(LIBS)

But it just failed miserably triggering about 100 errors all inside soplex.cpp (as in, it depends on -lgmp and -lz, but it could not find them? Too long to paste here)

I am pretty confused, any idea on how to fix this? thanks.

Answer 1

Try putting the $LIBS at the end of the command.

---

Change this:

LIBS = -L $(SOPLEXPATH) -lz -lgmp -lsoplex

Into this:

LIBS = -L $(SOPLEXPATH) -lsoplex -lgmp -lz

You always need to put B after A, if A calls functions in B. With static libraries as least.