Makefile - undefined reference to function - c

Question

I have a sample project that I'm working with from a book "Learn C the hard way". But I can't make it compile.
I believe there is a problem with my Makefile. What I'm trying to do is build a library and then call some functions from it. But when compiling tests I get
cthehardway/dlib/tests/list_tests.c:36: undefined reference to `List_pop'
Here is my Makefile:
CFLAGS=-g -O2 -Wall -Wextra -Isrc -rdynamic -DNDEBUG $(OPTFLAGS)
LIBS=-ldl $(OPTLIBS)
PREFIX?=/usr/local
SOURCES=$(wildcard src/**/*.c src/*.c)
OBJECTS=$(patsubst %.c,%.o,$(SOURCES))
TEST_SRC=$(wildcard tests/*_tests.c)
TESTS=$(patsubst %.c,%,$(TEST_SRC))
TARGET=build/libd.a
SO_TARGET=$(patsubst %.a,%.so,$(TARGET))
# The Target Build
all: $(TARGET) $(SO_TARGET) tests
dev: CFLAGS=-g -Wall -Isrc -Wall -Wextra $(OPTFLAGS)
dev: all
$(TARGET): CFLAGS += -fPIC
$(TARGET): build $(OBJECTS)
ar rcs $# $(OBJECTS)
ranlib $#
$(SO_TARGET): $(TARGET) $(OBJECTS)
$(CC) -shared -o $# $(OBJECTS)
build:
#mkdir -p build
#mkdir -p bin
# The Unit Tests
.PHONY: tests
tests: CFLAGS += $(TARGET)
tests: $(TESTS)
sh ./tests/runtests.sh
# The Cleaner
clean:
rm -rf build $(OBJECTS) $(TESTS)
rm -f tests/tests.log
find . -name "*.gc*" -exec rm {} \;
rm -rf `find . -name "*.dSYM" -print`
# The Install
install: all
install -d $(DESTDIR)/$(PREFIX)/lib/
install $(TARGET) $(DESTDIR)/$(PREFIX)/lib/
# The Checker
check:
#echo Files with potentially dangerous functions.
#egrep '[^_.>a-zA-Z0-9](str(n?cpy|n?cat|xfrm|n?dup|str|pbrk|tok|_)\
|stpn?cpy|a?sn?printf|byte_)' $(SOURCES) || true
And here is the link to the project itself (it is small, couple of files);
The project is dlib folder, disregard outside files.
Only the tests target fails. The library builds fine.
https://github.com/Voley/cthehardway

Answer 1

You're not including your library in the link of the test.
$(SO_TARGET): $(TARGET) $(OBJECTS)
$(CC) -shared -o $# $(OBJECTS)
You should include $(TARGET) in the bottom line.
At least, I think that's the case. It's a dependency, so I assume you want to link with it.